Three beta-decaying states in 128In and 130In resolved for the first time using Penning-trap techniques

Isomeric states in 128In and 130In have been studied with the JYFLTRAP Penning trap at the IGISOL facility. By employing state-of-the-art ion manipulation techniques, three different beta-decaying states in 128In and 130In have been separated and their masses measured. JYFLTRAP was also used to select the ions of interest for identification at a post-trap decay spectroscopy station. A new beta-decaying high-spin isomer feeding the isomer in 128Sn has been discovered in 128In at 1797.6(20) keV. Shell-model calculations employing a CD-Bonn potential re-normalized with the perturbative G-matrix approach suggest this new isomer to be a 16⁺ spin-trap isomer. In 130In, the lowest-lying (10⁻) isom…

Total absorption γ -ray spectroscopy of niobium isomers

15 pags. 17 figs., 5 tabs.

Model independent determination of the spin of theTa180naturally occurring isomer

The hyperfine structures of the 33715.27 ${\mathrm{cm}}^{\ensuremath{-}1}$ and 33706.47 ${\mathrm{cm}}^{\ensuremath{-}1}$ transitions from the ground state of singly ionized Ta have been measured by collinear laser spectroscopy. The structures were found to contain a large second order contribution. From fitting the observed hyperfine components for both $^{181}\mathrm{Ta}$ and the $^{180}\mathrm{Ta}$ naturally occurring isomer it was possible to determine the first and second order hyperfine structure coefficients. As no model independent determination of the nuclear spin of the $^{180}\mathrm{Ta}$ isomer has been performed, fitting was attempted for a range of spins. A clear chi-squared m…

Precision mass measurements on neutron-rich rare-earth isotopes at JYFLTRAP - reduced neutron pairing and implications for the $r$-process calculations

The rare-earth peak in the $r$-process abundance pattern depends sensitively on both the astrophysical conditions and subtle changes in nuclear structure in the region. This work takes an important step elucidating the nuclear structure and reducing the uncertainties in $r$-process calculations via precise atomic mass measurements at the JYFLTRAP double Penning trap. $^{158}$Nd, $^{160}$Pm, $^{162}$Sm, and $^{164-166}$Gd have been measured for the first time and the precisions for $^{156}$Nd, $^{158}$Pm, $^{162,163}$Eu, $^{163}$Gd, and $^{164}$Tb have been improved considerably. Nuclear structure has been probed via two-neutron separation energies $S_{2n}$ and neutron pairing energy metrics…

The MARA-LEB ion transport system

Abstract A low-energy branch is under development for the MARA vacuum-mode recoil separator at the Accelerator Laboratory of the University of Jyvaskyla. This development will allow for the study of proton-rich nuclei through laser ionisation spectroscopy and mass measurements. After stopping and extraction from a buffer gas cell, the ions of interest will be accelerated and transported to dedicated experimental setups by an ion transport system consisting of several focusing, accelerating and mass-separating elements. This article presents the current design and simulations for the ion transport.

Excited states in Br87 populated in β decay of Se87

Evidence for Increased neutron and proton excitations between 51−63 Mn

The hyperfine structures of the odd-even 51−63Mnatoms (N=26 −38) were measured using bunched beam collinear laser spectroscopy at ISOLDE, CERN. The extracted spins and magnetic dipole moments have been compared to large-scale shell-model calculations using different model spaces and effective interactions. In the case of 61,63Mn, the results show the increasing importance of neutron excitations across the N=40subshell closure, and of proton excitations across the Z=28shell gap. These measurements provide the first direct proof that proton and neutron excitations across shell gaps are playing an important role in the ground state wave functions of the neutron-rich Mn isotopes. publisher: Els…

First isomeric yield ratio measurements by direct ion counting and implications for the angular momentum of the primary fission fragments

We report the first experimental determination of independent isomeric yield ratios using direct ion counting with a Penning trap, which offered such a high resolution in mass that isomeric states could be separated. The measurements were performed at the Ion Guide Isotope Separator On-Line (IGISOL) facility at the University of Jyvaskyla. The isomer production ratios of Ge-81, Y-96,Y-97 Sn-128(,1)30, and Sb-129 in the 25-MeV proton-induced fission of U-na(t) and Th-232 were studied. Three isomeric pairs (Ge-81, Y-96, and Sb-129) were measured for the first time for the U-na(t)(p, f) reaction, while all the reported yield ratios for the Th-232(p, f) reaction were determined for the first ti…

First determination of β-delayed multiple neutron emission beyond A = 100 through direct neutron measurement : The P2n value of 136Sb

Background: β-delayed multiple neutron emission has been observed for some nuclei with A≤100, being the Rb100 the heaviest β2n emitter measured to date. So far, only 25P2n values have been determined for the ≈300 nuclei that may decay in this way. Accordingly, it is of interest to measure P2n values for the other possible multiple neutron emitters throughout the chart of the nuclides. It is of particular interest to make such a measurement for nuclei with A>100 to test the predictions of theoretical models and simulation tools for the decays of heavy nuclei in the region of very neutron-rich nuclei. In addition, the decay properties of these nuclei are fundamental for the understanding of a…

Experimental study of 100Tc β decay with total absorption γ -ray spectroscopy

The β decay of 100Tc has been studied by using the total absorption γ -ray spectroscopy technique at the Ion Guide Isotope Separator On-Line facility in Jyväskylä. In this work the new Decay Total Absorption γ -ray Spectrometer in coincidence with a cylindrical plastic β detector has been employed. The β intensity to the ground state obtained from the analysis is in good agreement with previous high-resolution measurements. However, differences in the feeding to the first-excited state as well as weak feeding to a new level at high excitation energy have been deduced from this experiment. Theoretical calculations performed in the quasiparticle random-phase approximation framework are also r…

Total absorption studies of high priority decays for reactor applications: 86Br and 91Rb

Preliminary results from beta decay studies of nuclei that are important for reactor applications are presented. The beta decays have been studied using the total absorption technique (TAS) and the pure beams provided by the JYFLTRAP system at the IGISOL facility of the University of Jyväskylä. peerReviewed

New accurate measurements of neutron emission probabilities for relevant fission products

We have performed new accurate measurements of the beta-delayed neutron emission probability for ten isotopes of the elements Y, Sb, Te and I. These are fission products that either have a significant contribution to the fraction of delayed neutrons in reactors or are relatively close to the path of the astrophysical r process. The measurements were performed with isotopically pure radioactive beams using a constant and high efficiency neutron counter and a low noise beta detector. Preliminary results are presented for six of the isotopes and compared with previous measurements and theoretical calculations. peerReviewed

Precision Mass Measurements on Neutron-Rich Rare-Earth Isotopes at JYFLTRAP : Reduced Neutron Pairing and Implications for r-Process Calculations

The rare-earth peak in the r-process abundance pattern depends sensitively on both the astrophysical conditions and subtle changes in nuclear structure in the region. This work takes an important step towards elucidating the nuclear structure and reducing the uncertainties in r-process calculations via precise atomic mass measurements at the JYFLTRAP double Penning trap. Nd158, Pm160, Sm162, and Gd164-166 have been measured for the first time, and the precisions for Nd156, Pm158, Eu162,163, Gd163, and Tb164 have been improved considerably. Nuclear structure has been probed via two-neutron separation energies S2n and neutron pairing energy metrics Dn. The data do not support the existence of…

Study of the β decay of fission products with the DTAS detector

Total Absorption Spectroscopy measurements of the β decay of 103Mo and 103Tc, important contributors to the decay heat summation calculation in reactors, are reported in this work. The analysis of the experiment, performed at IGISOL with the new DTAS detector, show new β intensity that was not detected in previous measurements with Ge detectors. peerReviewed

Single and Double Beta-DecayQValues among the TripletZr96,Nb96, andMo96

The atomic mass relations among the mass triplet ^{96}Zr, ^{96}Nb, and ^{96}Mo have been determined by means of high-precision mass measurements using the JYFLTRAP mass spectrometer at the IGISOL facility of the University of Jyvaskyla. We report Q values for the ^{96}Zr single and double β decays to ^{96}Nb and ^{96}Mo, as well as the Q value for the ^{96}Nb single β decay to ^{96}Mo, which are Q_{β}(^{96}Zr)=163.96(13), Q_{ββ}(^{96}Zr)=3356.097(86), and Q_{β}(^{96}Nb)=3192.05(16)  keV. Of special importance is the ^{96}Zr single β-decay Q value, which has never been determined directly. The single β decay, whose main branch is fourfold unique forbidden, is an alternative decay path to the…

Total absorption study of the \beta decay of 102,104,105Tc

The β-feeding probabilities for three important contributors to the decay heat in nuclear reactors, namely 102,104,105Tc, have been measured using the total absorption spectroscopy technique. For the measurements, sources of very high isobaric purity have been obtained using a Penning trap (JYFLTRAP). A detailed description of the data analysis is given and the results are compared with high-resolution measurements and theoretical calculations. peerReviewed

Fission studies at IGISOL/JYFLTRAP: Simulations of the ion guide for neutron-induced fission and comparison with experimental data

For the production of exotic nuclei at the IGISOL facility, an ion guide for neutron-induced fission has been developed and tested in experiments. Fission fragments are produced inside the ion guide and collected using a helium buffer gas. Meanwhile, a GEANT4 model has been developed to simulate the transportation and stopping of the charged fission products. In a recent measurement of neutron-induced fission yields, implantation foils were located at different positions in the ion guide. The gamma spectra from these foils and the fission targets are compared to the results from the GEANT4 simulation. In order to allow fission yield measurements in the low yield regions, towards the tails a…

Penning-trap-assisted study of excitations in Br88 populated in β decay of Se88

Excited levels of $^{88}\mathrm{Br}$ populated in the $\ensuremath{\beta}$ decay of $^{88}\mathrm{Se}$ have been studied by means of $\ensuremath{\beta}\ensuremath{\gamma}$ and $\ensuremath{\gamma}\ensuremath{\gamma}$ spectroscopy methods. Neutron-rich parent $^{88}\mathrm{Se}$ nuclei were produced with proton-induced fission of $^{238}\mathrm{U}$ using the Ion Guide Isotope Separator On-Line (IGISOL) method and separated from contaminants using a dipole magnet and the coupled JYFLTRAP Penning trap at the Accelerator Laboratory of the University of Jyv\"askyl\"a. The level scheme of $^{88}\mathrm{Br}$ has been constructed and $logft$ values of levels were determined. The ground-state spin o…

Signatures of oblate deformation in the ^{111}Tc nucleus

Monoisotopic samples of exotic, neutron-rich ${}^{111}$Mo nuclei, produced in the deuteron-induced fission of ${}^{238}$U and separated using the IGISOL3 isotope separator, coupled to the JYFLTRAP Penning trap, were used to perform $\ensuremath{\beta}$- and $\ensuremath{\gamma}$-coincidence spectroscopy of ${}^{111}$Tc. New excited levels in ${}^{111}$Tc populated in ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay of ${}^{111}$Mo provide the first indication for an oblate deformation in the mass $A\ensuremath{\approx}110$ region. The wide spin range of levels populated in ${}^{111}$Tc following the decay of ${}^{111}$Mo indicates the existence of two $\ensuremath{\beta}$-decaying levels in ${…

Separation of atomic and molecular ions by ion mobility with an RF carpet

Gas-filled stopping cells are used at accelerator laboratories for the thermalization of high-energy radioactive ion beams. Common challenges of many stopping cells are a high molecular background of extracted ions and limitations of extraction efficiency due to space-charge effects. At the FRS Ion Catcher at GSI, a new technique for removal of ionized molecules prior to their extraction out of the stopping cell has been developed. This technique utilizes the RF carpet for the separation of atomic ions from molecular contaminant ions through their difference in ion mobility. Results from the successful implementation and test during an experiment with a 600~MeV/u $^{124}$Xe primary beam are…

Precision experiments on exotic nuclei at IGISOL

Abstract Cooling and trapping techniques of low-energy radioactive ion beams of refractory elements employed at the IGISOL facility are presented with emphasis on high-precision measurements of the ground state properties of exotic nuclei. The impact of the new generation Paul and Penning traps on mass measurements of short-lived nuclei is discussed with examples on precision measurements of masses of super-allowed beta emitters and neutron-rich nuclei. As a new concept the trap-assisted spectroscopy of radioactive ions is presented with applications in collinear laser spectroscopy, decay spectroscopy of isobarically purified sources and in nuclear cross-section measurements by ion counting.

Magnetic octupole moment of Yb-173 using collinear laser spectroscopy

The hyperfine constants of the $4{f}^{14}6s6p^{3}P_{2}^{o}$ state in neutral Yb have been measured using three different dipole transitions. This state was recently shown to have a comparatively large hyperfine magnetic octupole splitting, and thus a puzzlingly large magnetic octupole moment. The measurement is performed using collinear laser spectroscopy on a fast atomic beam, which provides a straightforward route to probing long-lived metastable atomic states with high resolution. From the combined analysis of all three lines we find no significant evidence for a nonzero octupole moment in $^{173}\mathrm{Yb}$.

Characterization of a neutron–beta counting system with beta-delayed neutron emitters

A new detection system for the measurement of beta-delayed neutron emission probabilities has been characterized using fission products with well known β-delayed neutron emission properties. The setup consists of BELEN-20, a 4π neutron counter with twenty 3He proportional tubes arranged inside a large polyethylene neutron moderator, a thin Si detector for β counting and a selftriggering digital data acquisition system. The use of delayed-neutron precursors with different neutron emission windows allowed the study of the effect of energy dependency on neutron, β and β-neutron rates. The observed effect is well reproduced by Monte Carlo simulations. The impact of this dependency on the accura…

Mass ofAl23for testing the isobaric multiplet mass equation

The mass excess of the proton-rich nucleus $^{23}\mathrm{Al}$ has been measured with the JYFLTRAP Penning trap setup. As a result of our experiment we obtain a mass excess of 6748.07(34) keV, and by combining the value to existing experimental data we have tested the validity of the isobaric multiplet mass equation $(\mathrm{IMME})$ for the $T=3/2$ quartet in the $A=23$ isobar. The fit to the IMME results in a vanishing cubic term equivalent to zero with high precision [$0.22(42)$ keV].

Collinear laser spectroscopy of stable palladium isotopes at the IGISOL facility

AbstractCollinear laser spectroscopy on stable palladium isotopes was performed at the IGISOL facility in Jyväskylä in preparation for an experiment on its neutron-rich isotopes. Five transitions from different initial atomic states were tested, with the goal of finding the most spectroscopically efficient. The observed intensities afforded a comparison with atomic-level population predictions based on charge-exchange calculations. For some transitions hyperfine parameters of 105Pd were measured, which were found to be in good agreement with literature values. A King plot analysis was performed using the measured isotope shifts and known charge radii from literature to determine the atomic …

Discovery of an Exceptionally Strong β -Decay Transition of F20 and Implications for the Fate of Intermediate-Mass Stars

A significant fraction of stars between 7 and 11 solar masses are thought to become supernovae, but the explosion mechanism is unclear. The answer depends critically on the rate of electron capture on ^{20}Ne in the degenerate oxygen-neon stellar core. However, because of the unknown strength of the transition between the ground states of ^{20}Ne and ^{20}F, it has not previously been possible to fully constrain the rate. By measuring the transition, we establish that its strength is exceptionally large and that it enhances the capture rate by several orders of magnitude. This has a decisive impact on the evolution of the core, increasing the likelihood that the star is (partially) disrupte…

Towards commissioning the new IGISOL-4 facility

Abstract The Ion Guide Isotope Separator On-Line facility at the Accelerator Laboratory of the University of Jyvaskyla is currently being re-commissioned as IGISOL-4 in a new experimental hall. Access to intense beams of protons and deuterons from a new MCC30/15 cyclotron, with continued possibility to deliver heavy-ion beams from the K = 130 MeV cyclotron, offers extensive opportunities for long periods of fundamental experimental research, developments and applications. A new layout of beam lines with a considerable increase in floor space offers new modes of operation at the facility, as well as a possibility to incorporate more complex detector setups. We present a general overview of I…

Electron capture on116In and implications for nuclear structure related to double-βdecay

The electron capture decay branch of ${}^{116}$In has been measured to be $[2.46\ifmmode\pm\else\textpm\fi{}0.44(\mathrm{stat}.)\ifmmode\pm\else\textpm\fi{}0.39(\mathrm{syst}.)]\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ using Penning trap-assisted decay spectroscopy. The corresponding Gamow-Teller transition strength is shown to be compatible with the most recent value extracted from the $(p,n)$ charge-exchange reaction, providing a resolution to longstanding discrepancies. This transition can now be used as a reliable benchmark for nuclear-structure calculations of the matrix element for the neutrinoless double-$\ensuremath{\beta}$ decay of ${}^{116}$Cd and other nuclides.

Nuclear mean-square charge radii of63,64,66,68−82Ga nuclei: No anomalous behavior atN=32

Collinear laser spectroscopy was performed on the ${}^{63,64,66,68\ensuremath{-}82}$Ga isotopes with neutron numbers from $N=32$ to $N=51$. These measurements were carried out at the ISOLDE radioactive ion beam facility at CERN. Here we present the nuclear mean-square charge radii extracted from the isotope shifts and, for the lighter isotopes, new spin and moment values. New ground-state nuclear spin and moments were extracted from the hyperfine spectra of ${}^{63,70}$Ga, measured on an atomic transition in the neutral atom. The ground-state spin of ${}^{63}$Ga is determined to be $I=3/2$. Analysis of the trend in the change in mean-square charge radii of the gallium isotopes demonstrates …

Upgrades to the collinear laser spectroscopy experiment at the IGISOL

Abstract We give an overview of recent changes to the collinear laser spectroscopy beamline in the IGISOL laboratory. We present a new data acquisition system, commissioning of a newly installed charge exchange cell, and cooler-voltage calibration measurements. Currently ongoing modifications to the RFQ cooler-buncher are also discussed.

High-Precision Proton-Capture Q Values for 25Al(p,γ)26Si and 30P(p,γ)31Si

The masses of astrophysically relevant nuclei, 25Al and 30P, have recently been measured with the JYFLTRAP double Penning trap at the new IGISOL-4 facility at the University of Jyväskylä. Unparalleled precisions of 63 and 64 eV were achieved for the 25Al and 30P masses, respectively. The proton-capture Q values for 25Al(p, γ)26Si and 30P(p, γ)31S were also determined, and their precisions improved by a factor of 4 and 2, respectively, in comparison with AME12. The impact of the more precise values on the resonant proton-capture rate has also been studied. peerReviewed

Developments for neutron-induced fission at IGISOL-4

At the IGISOL-4 facility, neutron-rich, medium mass nuclei have usually been produced via charged particle-induced fission of natural uranium and thorium. Neutron-induced fission is expected to have a higher production cross section of the most neutron-rich species. Development of a neutron source along with a new ion guide continues to be one of the major goals since the commissioning of IGISOL-4. Neutron intensities at di↵erent angles from a beryllium neutron source have been measured in an on-line experiment with a 30 MeV proton beam. Recently, the new ion guide coupled to the neutron source has been tested as well. Details of the neutron source and ion guide design together with prelimi…

Development of a laser ion source at IGISOL

FURIOS, the Fast Universal laser IOn Source, is under development at the IGISOL (Ion Guide Isotope Separator On-Line) mass separator facility in Jyvaskyla, Finland. This new laser ion source will combine a state-of-the-art solid state laser system together with a dye laser system, for the selective and efficient production of exotic radioactive species without compromising the universality and fast release inherent in the IGISOL system. The motivation for, and development of, this ion source is discussed in relation to the programme of research ongoing at this mass separator facility.

Isotope shifts in natural cerium

High resolution crossed beam resonance fluorescence laser spectroscopy has been performed on an atomic beam of naturally occurring cerium, and isotope shifts have been measured in several transitions. Changes in mean square charge radius, δ〈r 2〉, have been extracted using the King plot technique and show the characteristic increase at the N = 82 neutron shell closure. The measurements form the basis for further investigations of radioactive isotopes and isomers on both sides of the shell closure.

Cryogenic helium as stopping medium for high-energy ions

We have investigated the survival and transport efficiency of Ra-219 ions emitted by a Ra-223 source in high-density cryogenic helium gas, with ionisation of the gas induced by a proton beam. The combined efficiency of ion survival and transport by an applied electric field was measured as a function of ionisation rate density for electric fields up to 160 V/cm and for three temperature and density combinations: 77 K, 0.18 mg/cm(3), 10 K, 0.18 mg/cm(3) and 10 K, 0.54 mg/cm(3). At low beam intensity or high electric field, an efficiency of 30%, is obtained, confirming earlier results. A sharp drop in efficiency is observed at a "threshold" ionisation rate density which increases with the squ…

Super-Allowed β Decay of23Mg Studied with a High-Precision Germanium Detector

Development of a saturated absorption spectroscopy setup at IGISOL for characterisation of Fabry-Pérot interferometers

A saturated absorption spectroscopy setup was developed and optimised for the characterisation of a home-built and a commercial Fabry-Pérot interferometer (FPI). The free spectral range of these FPIs has been determined with reliable statistical and systematic errors. These FPIs will be used for accurate wavelength determination of broad- and narrowband pulsed Ti:sapphire lasers used in resonance ionisation spectroscopy experiments. peerReviewed

Large Impact of the Decay of Niobium Isomers on the Reactor ¯νe Summation Calculations

Even mass neutron-rich niobium isotopes are among the principal contributors to the reactor antineutrino energy spectrum. They are also among the most challenging to measure due to the refractory nature of niobium, and because they exhibit isomeric states lying very close in energy. The β-intensity distributions of 100gs;100mNb and 102gs;102mNb β decays have been determined using the total absorption γ-ray spectroscopy technique. The measurements were performed at the upgraded Ion Guide Isotope Separator On-Line facility at the University of Jyväskylä. Here, the double Penning trap system JYFLTRAP was employed to disentangle the β decay of the isomeric states. The new data obtained in this …

Retention of Pb isotopes in glass surfaces for retrospective assessment of radon exposure

Abstract In recent years there has been increasing interest in radio-epidemiological techniques to retrospectively measure the radon dose exposure by determining the activity of 210Pb, the longest-lived 222Rn progeny, in glass surface layers. In this study the diffusion of 39 keV 209Pb+ ions implanted into glass using the IGISOL facility has been studied under conditions that mimic the recoil implantation of 210Pb from 222Rn. The resulting depth distributions of 209Pb were then measured after heat treatment in vacuum at different temperatures by a sputter erosion technique. The diffusion coefficient could be described by an Arrhenius equation D = D0exp(−H/kT) where D 0 = 0.30 - 0.24 + 1.14 …

Total absorption γ -ray spectroscopy of the β -delayed neutron emitters I137 and Rb95

The decays of the β-delayed neutron emitters I137 and Rb95 have been studied with the total absorption γ-ray spectroscopy technique. The purity of the beams provided by the JYFLTRAP Penning trap at the ion guide isotope separator on-line facility in Jyvaskyla allowed us to carry out a campaign of isotopically pure measurements with the decay total absorption γ-ray spectrometer, a segmented detector composed of 18 NaI(Tl) modules. The contamination coming from the interaction of neutrons with the spectrometer has been carefully studied, and we have tested the use of time differences between prompt γ rays and delayed neutron interactions to eliminate this source of contamination. Due to the s…

Internal conversion from excited electronic states of 229Th ions

The process of internal conversion from excited electronic states is investigated theoretically for the case of the vacuum-ultraviolet nuclear transition of 229Th. Due to the very low transition energy, the 229Th nucleus offers the unique possibility to open the otherwise forbidden internal conversion nuclear decay channel for thorium ions via optical laser excitation of the electronic shell. We show that this feature can be exploited to investigate the isomeric state properties via observation of internal conversion from excited electronic configurations of Th+ and Th2+ ions. A possible experimental realization of the proposed scenario at the nuclear laser spectroscopy facility IGISOL in J…

Measurement of the heaviest Beta-delayed 2-neutron emitter: 136Sb

The Beta-delayed neutron emission probability, Pn , of very exotic nuclei is crucial for the understanding of nuclear structure properties of many isotopes and astrophysical processes such as the rapid neutron capture process (r-process). In addition Beta-delayed neutrons are important in a nuclear power reactor operated in a prompt sub-critical, delayed critical condition, as they contribute to the decay heat inducing fission reactions after a shut down. The study of neutron-rich isotopes and the measurement of Beta-delayed one-neutron emitters (Beta1n) is possible thanks to the Rare Isotope Beam (RIB) facilities, where radioactive beams allow the production of exotic nuclei of interest, w…

Characterization of a cylindrical plastic β-detector with Monte Carlo simulations of optical photons

In this work we report on the Monte Carlo study performed to understand and reproduce experimental measurements of a new plastic β-detector with cylindrical geometry. Since energy deposition simulations differ from the experimental measurements for such a geometry, we show how the simulation of production and transport of optical photons does allow one to obtain the shapes of the experimental spectra. Moreover, taking into account the computational effort associated with this kind of simulation, we develop a method to convert the simulations of energy deposited into light collected, depending only on the interaction point in the detector. This method represents a useful solution when extens…

Design, construction and cooling system performance of a prototype cryogenic stopping cell for the Super-FRS at FAIR

A cryogenic stopping cell for stopping energetic radioactive ions and extracting them as a low energy beam was developed. This first ever cryogenically operated stopping cell serves as prototype device for the Low-Energy Branch of the Super-FRS at FAIR. The cell has a stopping volume that is 1 m long and 25 cm in diameter. Ions are guided by a DC field along the length of the stopping cell and by a combined RF and DC fields provided by an RE carpet at the exit-hole side. The ultra-high purity of the stopping gas required for optimum ion survival is reached by cryogenic operation. The design considerations and construction of the cryogenic stopping cell, as well as some performance character…

Determination of β -decay ground state feeding of nuclei of importance for reactor applications

12 pags., 6 figs., 3 tabs.

Independent Isotopic Product Yields in 25 MeV and 50 MeV Charged Particle Induced Fission of 238U and 232Th

Abstract Independent isotopic yields for most elements from Zn to La in 25-MeV proton-induced fission of 238U and 232Th have been determined at the IGISOL facility in the University of Jyvaskyla. In addition, isotopic yields for Zn, Ga, Rb, Sr, Zr, Pd and Xe in 50-MeV proton-induced fission of 238U and for Zn, Ga, Rb, Sr, Cd and In in 25-MeV deuterium-induced fission of 238U have been measured. The utilised technique recently developed at the University of Jyvaskyla, is based on a combination of the ion guide technique and the ability of a Penning trap to unambiguously identify the isotopes by their atomic mass. Since the yields are determined by ion counting, no prior knowledge beyond the …

Precise measurements of half-lives and branching ratios for the ββ mirror transitions in the decay of 23Mg and 27Si

Half-lives and branching ratios for the two mirror ββ decays of 23Mg and 27Si have been measured at the University of Jyväskylä with the IGISOL facility. The results obtained, T1/2=11.303(3)T1/2=11.303(3) s and T1/2=4.112(2)T1/2=4.112(2) s for the half-lives of 23Mg and 27Si , respectively, are 7 and 8 times more precise than the averages of previous measurements. The values obtained for the super-allowed branching ratios of 23Mg and 27Si are B.R.=92.18(8)%B.R.=92.18(8)% and B.R.=99.74(2)%B.R.=99.74(2)% , respectively. The result for 23Mg is three times more precise than the average of the previous measurements, while for 27Si the precision has not been improved, the average of the previous…

Mass measurements in the vicinity of the doubly magic waiting pointNi56

Masses of $^{56,57}\mathrm{Fe}$, $^{53}\mathrm{Co}$${}^{m}$, $^{53,56}\mathrm{Co}$, $^{55,56,57}\mathrm{Ni}$, $^{57,58}\mathrm{Cu}$, and $^{59,60}\mathrm{Zn}$ have been determined with the JYFLTRAP Penning trap mass spectrometer at the Ion-Guide Isotope Separator On-Line facility with a precision of $\ensuremath{\delta}m/m\ensuremath{\leqslant}3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$. The ${Q}_{\mathrm{EC}}$ values for $^{53}\mathrm{Co}$, $^{55}\mathrm{Ni}$, $^{56}\mathrm{Ni}$, $^{57}\mathrm{Cu}$, $^{58}\mathrm{Cu}$, and $^{59}\mathrm{Zn}$ have been measured directly with a typical precision of better than $0.7 \mathrm{keV}$ and Coulomb displacement energies have been dete…

Rate capability of a cryogenic stopping cell for uranium projectile fragments produced at 1000 MeV/u

At the Low-Energy Branch (LEB) of the Super-FRS at FAIR, projectile and fission fragments will be produced at relativistic energies, separated in-flight, energy-bunched, slowed down and thermalized in a cryogenic stopping cell (CSC) filled with ultra-pure He gas. The fragments are extracted from the stopping cell using a combination of DC and RF electric fields and gas flow. A prototype CSC for the LEB has been developed and successfully commissioned at the FRS Ion Catcher at GSI. Ionization of He buffer gas atoms during the stopping of energetic ions creates a region of high space charge in the stopping cell. The space charge decreases the extraction efficiency of stopping cells since the …

Total absorption γ-ray spectroscopy of the β-delayed neutron emitters 87Br, 88Br, and 94Rb

We investigate the decay of 87,88Br and 94Rb using total absorption γ -ray spectroscopy. These important fission products are β-delayed neutron emitters. Our data show considerable βγ intensity, so far unobserved in high-resolution γ -ray spectroscopy, from states at high excitation energy. We also find significant differences with the β intensity that can be deduced from existing measurements of the β spectrum. We evaluate the impact of the present data on reactor decay heat using summation calculations. Although the effect is relatively small it helps to reduce the discrepancy between calculations and integral measurements of the photon component for 235U fission at cooling times in the r…

High-precision mass measurements for the isobaric multiplet mass equation atA= 52

Masses of $^{52}$Co, $^{52}$Co$^m$, $^{52}$Fe, $^{52}$Fe$^m$, and $^{52}$Mn have been measured with the JYFLTRAP double Penning trap mass spectrometer. Of these, $^{52}$Co and $^{52}$Co$^m$ have been experimentally determined for the first time and found to be more bound than predicted by extrapolations. The isobaric multiplet mass equation for the $T=2$ quintet at $A=52$ has been studied employing the new mass values. No significant breakdown (beyond the $3\sigma$ level) of the quadratic form of the IMME was observed ($\chi^2/n=2.4$). The cubic coefficient was 6.0(32) keV ($\chi^2/n=1.1$). The excitation energies for the isomer and the $T=2$ isobaric analogue state in $^{52}$Co have been d…

Strong γ-ray emission from neutron unbound states populated in β-decay: Impact on (n,γ) cross-section estimates

J. L. Taín et al. -- 6 pags., 7 figs., 1 tab. -- Open Access funded by Creative Commons Atribution Licence 4.0

Laser spectroscopy with an electrostatic ConeTrap

A compact electrostatic trap has been designed and installed as part of the recent upgrades to the IGISOL IV facility. The ConeTrap provides an in vacuo optical pumping site for low energy (800 eV) ionic ensembles available for interaction periods of 10-100 ms. At present, 6.7(3) % of injected mass A=98 ions can be trapped, stored for 5 ms, extracted and transported to a laser-ion interaction region. This fraction represents those ions for which no perturbation to total energy or energy spread is observed. Proposed enhancements to the trap are designed to improve the trapping efficiency by up to a factor of 5. Differential pumping and reduction in background pressure below the present 10−6 …

New lifetime measurements inPd109and the onset of deformation atN=60

Several new subnanosecond lifetimes were measured in Pd-109 using the fast-timing beta gamma gamma (t) method. Fission fragments of the A = 109 mass chain were produced by bombarding natural uranium with 30 MeV protons at the Jyvaskyla Ion Guide Isotope Separator On-Line (IGISOL) facility. Lifetimes were obtained for excited states in Pd-109 populated following beta decay of Rh-109. The new lifetimes provide some insight into the evolution of nuclear structure in this mass region. In particular, the distinct structure of the two low-lying 7/2(+) states occurring systematically across the Pd isotopic chain is supported by the new lifetime measurements. The available nuclear data indicate a s…

Precision mass measurements of Fe67 and Co69,70 : Nuclear structure toward N=40 and impact on r -process reaction rates

Accurate mass measurements of neutron-rich iron and cobalt isotopes $^{67}\mathrm{Fe}$ and $^{69,70}\mathrm{Co}$ have been realized with the JYFLTRAP double Penning-trap mass spectrometer. With novel ion-manipulation techniques, the masses of the $^{69,70}\mathrm{Co}$ ground states and the $1/{2}^{\ensuremath{-}}$ isomer in $^{69}\mathrm{Co}$ have been extracted for the first time. The measurements remove ambiguities in the previous mass values and yield a smoother trend on the mass surface, extending it beyond $N=40$. The moderate $N=40$ subshell gap has been found to weaken below $^{68}\mathrm{Ni}$, a region known for shape coexistence and increased collectivity. The excitation energy for…

Precision Ga71–Ge71 mass-difference measurement

Abstract The Ga 71 ( ν e , e − ) Ge 71 reaction Q value has been measured with the JYFLTRAP mass spectrometer at the IGISOL facility of the University of Jyvaskyla to Q  = 232.443(93) keV. This value agrees with previous measurements, though it features a much higher accuracy. The Q value is being discussed in the context of the solar neutrino capture rate in Ga 71 .

Total Absorption Spectroscopy of Fission Fragments Relevant for Reactor Antineutrino Spectra and Decay Heat Calculations

Volume: 111 Host publication title: WONDER-2015 Host publication sub-title: 4TH INTERNATIONAL WORKSHOP ON NUCLEAR DATA EVALUATION FOR REACTOR APPLICATIONS Isbn(print): 978-2-7598-1970-6 Beta decay of fission products is at the origin of decay heat and antineutrino emission in nuclear reactors. Decay heat represents about 7% of the reactor power during operation and strongly impacts reactor safety. Reactor antineutrino detection is used in several fundamental neutrino physics experiments and it can also be used for reactor monitoring and non-proliferation purposes. Rb-92,Rb-93 are two fission products of importance in reactor antineutrino spectra and decay heat, but their beta-decay properti…

Characterization of a cryogenic ion guide at IGISOL

A small volume cryogenic ion guide has been characterized at the IGISOL facility, Jyvaskyla, as a prototype to verify whether there are any major obstacles to the use of high-density cryogenic helium gas for the stopping and extraction of high-energy ions from a large volume cryogenic ion catcher. The expected temperature scaling of the mass flow through the ion guide has been confirmed, showing that for the same helium density, the differential pumping requirements are less stringent for cryogenic operation. At 90 K a clear reduction in the mass-analyzed impurities is achieved, although lower temperatures are required to freeze out oxygen and nitrogen. This is supported by the reduction in…

Ground-state spins and moments of72,74,76,78Ga nuclei

Laser spectroscopy was performed on the ${}^{72,74,76,78}$Ga isotopes at On-Line Isotope Mass Separator (ISOLDE) facility, CERN. Ground-state nuclear spins and moments were extracted from the measured hyperfine spectra. The results are compared to shell-model calculations, which provide a detailed probe of the nuclear wave function. The spin is established from the shape of the hyperfine structure and the parity inferred from a comparison of shell-model calculations with the measured nuclear moments. The ground states of ${}^{76,78}$Ga are both assigned a spin and parity of ${I}^{\ensuremath{\pi}}={2}^{\ensuremath{-}}$, while ${}^{74}$Ga is tentatively assigned as ${I}^{\ensuremath{\pi}}={3…

Electron-capture branch ofTc100and tests of nuclear wave functions for double-βdecays

We present a measurement of the electron-capture branch of $^{100}\mathrm{Tc}$. Our value, $B(\mathrm{EC})=(2.6\ifmmode\pm\else\textpm\fi{}0.4)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$, implies that the $^{100}\mathrm{Mo}$ neutrino absorption cross section to the ground state of $^{100}\mathrm{Tc}$ is roughly 50% larger than previously thought. Disagreement between the experimental value and QRPA calculations relevant to double-$\ensuremath{\beta}$ decay matrix elements persists. We find agreement with previous measurements of the 539.5- and 590.8-keV $\ensuremath{\gamma}$-ray intensities.

Excited states in 31S studied via beta decay of 31Cl

The beta decay of 31Cl has been studied with a silicon detector array and a HPGe detector at the IGISOL facility. Previously controversial proton peaks have been confirmed to belong to 31Cl and a new proton group with an energy of 762(14) keV has been found. Proton captures to this state at 6921(15) keV in 31S can have an effect on the reaction rate of 30P(p,γ) in ONe novae. Gamma rays of 1249.1(14) keV and 2234.5(8) keV corresponding to the de-excitations of the first two excited states in 31S have been measured. No beta-delayed protons from the IAS have been observed. peerReviewed

Gamma/neutron competition above the neutron separation energy in delayed neutron emitters

To study the β-decay properties of some well known delayed neutron emitters an experiment was performed in 2009 at the IGISOL facility (University of Jyvaskyla in Finland) using Total Absorption -ray Spectroscopy (TAGS) technique. The aim of these measurements is to obtain the full β-strength distribution below the neutron separation energy (Sn) and the γ/neutron competition above. This information is a key parameter in nuclear technology applications as well as in nuclear astrophysics and nuclear structure. Preliminary results of the analysis show a significant γ-branching ratio above Sn. © Owned by the authors, published by EDP Sciences, 2014.

Precision Mass Measurements beyond $^{132}$Sn: Anomalous behaviour of odd-even staggering of binding energies

Atomic masses of the neutron-rich isotopes $^{121-128}$Cd, $^{129,131}$In, $^{130-135}$Sn, $^{131-136}$Sb, and $^{132-140}$Te have been measured with high precision (10 ppb) using the Penning trap mass spectrometer JYFLTRAP. Among these, the masses of four r-process nuclei $^{135}$Sn, $^{136}$Sb, and $^{139,140}$Te were measured for the first time. The data reveals a strong $N$=82 shell gap at $Z$=50 but indicates the importance of correlations for $Z>50$. An empirical neutron pairing gap expressed as the odd-even staggering of isotopic masses shows a strong quenching across $N$=82 for Sn, with the $Z$-dependence that is unexplainable by the current theoretical models.

$Q$-value of the superallowed $\beta$ decay of 62Ga

Masses of the radioactive isotopes 62Ga, 62Zn and 62Cu have been measured at the JYFLTRAP facility with a relative precision of better than 18 ppb. A Q_EC value of (9181.07 +- 0.54) keV for the superallowed decay of 62Ga is obtained from the measured cyclotron frequency ratios of 62Ga-62Zn, 62Ga-62Ni and 62Zn-62Ni ions. The resulting Ft-value supports the validity of the conserved vector current hypothesis (CVC). The mass excess values measured were (-51986.5 +-1.0) keV for 62Ga, (-61167.9 +- 0.9) keV for 62Zn and (-62787.2 +- 0.9) keV for 62Cu.

Proton-neutron pairing correlations in the self-conjugate nucleus 42Sc

Collinear laser spectroscopy of the N=Z=21 self-conjugate nucleus 42Sc has been performed at the JYFL IGISOL IV facility in order to determine the change in nuclear mean-square charge radius between the Iπ=0+ ground state and the Iπ=7+ isomer via the measurement of the 42g,42mSc isomer shift. New multi-configurational Dirac-Fock calculations for the atomic mass shift and field shift factors have enabled a recalibration of the charge radii of the 42−46Sc isotopes which were measured previously. While consistent with the treatment of proton-neutron, proton-proton and neutron-neutron pairing on an equal footing, the reduction in size for the isomer is observed to be of a significantly larger m…

Production of pure samples of 131mXe and 135Xe

Pure samples of (131m)Xe, (133m)Xe, (133)Xe and (135)Xe facilitate the calibration and testing of noble gas sampler stations and related laboratory instrumentation. We have earlier reported a Penning trap-based production method for pure (133m)Xe and (133)Xe samples. Here we complete the work by reporting the successful production of pure (131m)Xe and (135)Xe samples using the same technique. In addition, we present data on xenon release from graphite.

Simulations of the stopping efficiencies of fission ion guides

With the Ion Guide Isotope Separator On-Line (IGISOL) facility, located at the University of Jyväskylä, products of nuclear reactions are separated by mass. The high resolving power of the JYFLTRAP Penning trap, with full separation of individual nuclides, capacitates the study of nuclides far from the line of stability. For the production of neutron-rich medium-heavy nuclides, fissioning of actinides is a feasible reaction. This can be achieved with protons from an in-house accelerator or, alternatively, with neutrons through the addition of a newly developed Be(p,xn)-converter. The hereby-obtained fission products are used in nuclear data measurements, for example fission yields, nuclear …

Total absorption spectroscopy of fission fragments relevant for reactor antineutrino spectra

International audience; The accurate determination of reactor antineutrino spectra remains a very active research topic for which new methods of study have emerged in recent years. Indeed, following the long-recognized reactor anomaly (measured antineutrino deficit in short baseline reactor experiments when compared with spectral predictions), the three international reactor neutrino experiments Double Chooz, Daya Bay and Reno have recently demonstrated the existence of spectral distortions in their measurements with respect to the same predictions. These spectral predictions were obtained through the conversion of integral beta-energy spectra obtained at the ILL research reactor. Several s…

Characterization of 233U alpha recoil sources for 229()Th beam production

Radioactive $^{233}$U alpha recoil sources are being considered for the production of a thorium ion source to study the low-energy isomer in $^{229}$Th with high-resolution collinear laser spectroscopy at the IGISOL facility of the University of Jyv\"askyl\"a. In this work two different $^{233}$U sources have been characterized via alpha and gamma spectroscopy of the decay radiation obtained directly from the sources and from alpha-recoils embedded in implantation foils. These measurements revealed rather low $^{229}$Th recoil efficiencies of only a few percent. Although the low efficiency of one of the two sources can be attributed to its inherent thickness, the low recoil efficiency of th…

Low-spin excitations in the 109Tc nucleus

Monoisotopic samples of ${}^{109}$Mo nuclei, produced in the deuteron-induced fission of ${}^{238}$U and separated using the IGISOL mass separator coupled to a Penning trap, were used to perform $\ensuremath{\beta}$- and $\ensuremath{\gamma}$-coincidence spectroscopy of ${}^{109}$Tc. Spin and parity 5/2${}^{+}$ for the ground state of ${}^{109}$Mo, proposed earlier, are supported in the present work. Three new low-energy levels observed in ${}^{109}$Tc are interpreted as bandheads of the $\ensuremath{\pi}3/{2}^{\ensuremath{-}}$[301], $\ensuremath{\pi}5/{2}^{\ensuremath{-}}$[303], and $\ensuremath{\pi}1/{2}^{+}$[431] configurations, respectively. A further three levels observed around 0.4 Me…

Radioactive ion beam manipulation at the IGISOL-4 facility

The IGISOL-4 facility in the JYFL Accelerator Laboratory of the University of Jyvaskyla (JYFL-ACCLAB) produces low-energy radioactive ion beams, primarily for nuclear spectroscopy, utilizing an ion guide-based, ISOL-type mass separator. Recently, new ion manipulation techniques have been introduced at the IGISOL-4 including the application of the PI-ICR (Phase-Imaging Ion Cyclotron Resonance) technique at the JYFLTRAP Penning trap, as well as commissioning of a Multi-Reflection Time-Of-Flight (MR-TOF) separator/spectrometer. The successful operation of the MR-TOF also required significant improvement of the Radio-Frequency Quadrupole (RFQ) cooler and buncher device beam pulse time structure…

Upgrade and yields of the IGISOL facility

The front end of the Jyvaskyla IGISOL facility was upgraded in 2003 by increasing its pumping capacity and by improving the radiation shielding. In late 2005, the skimmer electrode of the mass separator was replaced by a sextupole ion guide, which improved the mass separator efficiency up to an order of magnitude. The current design of the facility is described. The updated yield data, achieved with and without the additional JYFLTRAP purification, using both fusion evaporation reactions and particle induced fission is presented to give an overview of the capability of the facility. These data have been determined either by radioactivity measurements or by direct ion counting after the Penn…

High-Precision Q -Value Measurement Confirms the Potential of Cs135 for Absolute Antineutrino Mass Scale Determination

The ground-state-to-ground-state $\ensuremath{\beta}$-decay $Q$ value of $^{135}\mathrm{Cs}(7/{2}^{+})\ensuremath{\rightarrow}^{135}\mathrm{Ba}(3/{2}^{+})$ has been directly measured for the first time. The measurement was done utilizing both the phase-imaging ion-cyclotron resonance technique and the time-of-flight ion-cyclotron resonance technique at the JYFLTRAP Penning-trap setup and yielded a mass difference of 268.66(30) keV between $^{135}\mathrm{Cs}(7/{2}^{+})$ and $^{135}\mathrm{Ba}(3/{2}^{+})$. With this very small uncertainty, this measurement is a factor of 3 more precise than the currently adopted $Q$ value in the Atomic Mass Evaluation 2016. The measurement confirms that the f…

Characterization of a neutron-beta counting system with beta-delayed neutron emitters

Abstract A new detection system for the measurement of beta-delayed neutron emission probabilities has been characterized using fission products with well known β-delayed neutron emission properties. The setup consists of BELEN-20, a 4π neutron counter with twenty 3He proportional tubes arranged inside a large polyethylene neutron moderator, a thin Si detector for β counting and a self-triggering digital data acquisition system. The use of delayed-neutron precursors with different neutron emission windows allowed the study of the effect of energy dependency on neutron, β and β–neutron rates. The observed effect is well reproduced by Monte Carlo simulations. The impact of this dependency on …

Total absorption γ-ray spectroscopy of beta delayed neutron emitters

Preliminary results of the data analysis of the beta decay of 94Rb using a novel - segmented- total absorption spectrometer are shown in this contribution. This result is part of a systematic study of important contributors to the decay heat problem in nuclear reactors. In this particular case the goal is to determine the beta intensity distribution below the neutron separation energy and the gamma/beta competition above.

Development of resonance ionization in a supersonic gas-jet for studies of short-lived and long-lived radioactive nuclei

High-resolution resonance ionization spectroscopy (RIS) is required for laser spectroscopy and trace analysis of short-lived and long-lived radioactive nuclei. We have proposed high-resolution resonance ionization spectroscopy in a gas jet combined with a narrow band-width injection-locked Ti:Sapphire laser. Resonance ionization of stable 93Nb in a gas jet was demonstrated using a broad bandwidth Ti:Sapphire laser. In addition, a setup for high-resolution RIS in a gas-jet was designed using numerical simulations of the gas-jet conditions based on computational fluid dynamics.

Efficient, high-resolution resonance laser ionization spectroscopy using weak transitions to long-lived excited states

Laser spectroscopic studies on minute samples of exotic radioactive nuclei require very efficient experimental techniques. In addition, high resolving powers are required to allow extraction of nu- clear structure information. Here we demonstrate that by using weak atomic transitions, resonance laser ionization spectroscopy is achieved with the required high efficiency (1-10%) and precision (linewidths of tens of MHz). We illustrate experimentally and through the use of simulations how the narrow experimental linewidths are achieved and how distorted resonance ionization spec- troscopy lineshapes can be avoided. The role of the delay of the ionization laser pulse with respect to the excitat…

The FRS Ion Catcher

At the FRS Ion Catcher at GSI, projectile and fission fragments are produced at relativistic energies, separated in-flight, range-focused, slowed down and thermalized in a cryogenic stopping cell. A multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS) is used to perform direct mass measurements and to provide an isobarically clean beam for further experiments, such as mass-selected decay spectroscopy. A versatile RF quadrupole transport and diagnostics unit guides the ions from the stopping cell to the MR-TOF-MS, provides differential pumping, ion identification and includes reference ion sources. The FRS Ion Catcher serves as a test facility for the Low-Energy Branch of the Sup…

Towards on-line production of N=Z94Ag at IGISOL

Abstract A future study of the ground state and low-lying isomeric states of 94 Ag and 96 Ag at the Ion Guide Isotope Separator On-Line (IGISOL) facility, University of Jyvaskyla, requires the development of a low-energy beam of neutron-deficient silver. In order to attain the highest possible extraction efficiencies the coupling of a hot cavity graphite catcher device to the IGISOL mass-separator is planned. A heavy-ion fusion-evaporation reaction will produce the silver recoils which will be captured in the graphite catcher. Resonant laser ionization techniques will be applied to efficiently and selectively ionize the evaporated silver atoms. A simulation program has been written to study…

Development of two-color resonance ionization scheme for Th using an automated wide-range tunable Ti:sapphire laser system

Two-color resonance ionization schemes of Th were investigated by an automated wide-range tunable, grating-assisted Ti:Sa laser system with intracavity SHG option. A two-color ionization scheme via autoionizing state (1st step: 372.049 nm and 2nd step: 401.031 nm) was developed and its relative efficiency was lower by factor of three compared to a known three color scheme. peerReviewed

Isomeric states close to doubly magic $^{132}$Sn studied with JYFLTRAP

The double Penning trap mass spectrometer JYFLTRAP has been employed to measure masses and excitation energies for $11/2^-$ isomers in $^{121}$Cd, $^{123}$Cd, $^{125}$Cd and $^{133}$Te, for $1/2^-$ isomers in $^{129}$In and $^{131}$In, and for $7^-$ isomers in $^{130}$Sn and $^{134}$Sb. These first direct mass measurements of the Cd and In isomers reveal deviations to the excitation energies based on results from beta-decay experiments and yield new information on neutron- and proton-hole states close to $^{132}$Sn. A new excitation energy of 144(4) keV has been determined for $^{123}$Cd$^m$. A good agreement with the precisely known excitation energies of $^{121}$Cd$^m$, $^{130}$Sn$^m$, an…

Structure of 115Ag studied by β− decays of 115Pd and 115mPd

The excited levels of 115Ag have been studied via the beta decay of 115Pd and 115Pdm. The beta-decay schemes for both states have been considerably extended, especially the scheme following the decay of 115Pdm which was practically unknown before this work. Transition intensities and log10 f t values are reported, which have been missing in the literature. A set of levels around 2 MeV has been found to be strongly populated by the beta decay of the ground state of 115Pd and is suggested to have a three-quasiparticle nature. The properties of excited levels have been compared with the level systematics of lighter neutron-rich silver isotopes, and new spin assignments as well as identificatio…

High-precision mass measurements of 25Al and 30P at JYFLTRAP

The masses of the astrophysically relevant nuclei 25Al and 30P have been measured with a Penning trap for the first time. The mass-excess values for 25Al ( $\Delta = -8915.962(63)$ keV) and 30P ( $\Delta = -20200.854(64)$ keV) obtained with the JYFLTRAP double Penning trap mass spectrometer are in good agreement with the Atomic Mass Evaluation 2012 values but $ \approx$ 5-10 times more precise. A high precision is required for calculating resonant proton-capture rates of astrophysically important reactions 25Al (p, $ \gamma$ )26Si and 30P(p, $ \gamma$ )31S . In this work, $ Q_{(p,\gamma)} = 5513.99(13)$ keV and $ Q_{(p,\gamma)} = 6130.64(24)$ keV were obtained for 25Al and 30P , respectivel…

Gas cell studies of thorium using filament dispensers at IGISOL

Abstract Filament-based dispensers of thorium have been investigated at the IGISOL facility, Jyvaskyla, for potential use as a thorium ion source for future collinear laser spectroscopy experiments. Several different filaments were manufactured in the Institute of Atomic and Subatomic Physics of TU Wien, with 232Th and 229Th prepared on tantalum substrates either by drying thorium nitrate solution or via molecular plating, while adding a layer of zirconium for oxide reduction. The filaments were characterized in a helium-filled gas cell by performing selective and efficient in-gas-cell resonance laser ionization and by analyzing the resulting ion beams by mass spectrometry. Additionally, th…

The shape transition in the neutron-rich yttrium isotopes and isomers

Abstract Laser spectroscopy has been used to study 86–90,92–102Y and isomeric states of 87–90,93,96,97,98Y. Nuclear charge radii differences, magnetic dipole and electric quadrupole moments have been obtained. Information on the nature of the Z ≈ 40 , N ≈ 60 sudden onset of deformation has been derived from all three parameters. It is seen that with increasing neutron number from the N = 50 shell closure that the nuclear deformation becomes increasingly oblate and increasingly soft. At N = 60 a transition to a strongly deformed rigid prolate shape occurs but prior to this, although the nuclear deformation is increasing with N, a proportionate increase in softness is also observed.

Half-life, branching-ratio, andQ-value measurement for the superallowed0+→0+β+emitterTi42

The half-life, the branching ratio, and the decay $Q$ value of the superallowed $\ensuremath{\beta}$ emitter $^{42}\mathrm{Ti}$ were measured in an experiment performed at the JYFLTRAP facility of the Accelerator Laboratory of the University of Jyv\"askyl\"a. $^{42}\mathrm{Ti}$ is the heaviest ${T}_{z}=\ensuremath{-}1$ nucleus for which high-precision measurements of these quantities have been tried. The half-life (${T}_{1/2}=208.14\ifmmode\pm\else\textpm\fi{}0.45$ ms) and the $Q$ value [${Q}_{\mathrm{EC}}=7016.83(25)$ keV] are close to or reach the required precision of about 0.1%. The branching ratio for the superallowed decay branch [$\mathrm{BR}=47.7(12)%$], a by-product of the half-lif…

New concepts for the ion guide technique

The technique of using noble gases to cool energetic beams offers fast extraction times, very little sensitivity to chemical properties of the ions and very low-energy spreads. A variant of this method is based on the selective laser ionization of radioactive species after they have been thermalized in gas as neutral atoms. The laser ion source in Jyvaskyla is used to highlight the importance of buffer gas purity using yttrium, a particularly chemically reactive element. The time distribution profiles obtained on-line illustrate the competing factors that create and destroy the ion of interest during evacuation from the ion guide. A review of the extraction efficiencies of gas catchers of d…

A study of on-line gas cell processes at IGISOL

Abstract The laser ion source at the IGISOL facility, Jyvaskyla, has been used to study the effects of the passage of a primary beam through an ion guide via the dynamic time profiles of yttrium and related molecular compounds. The accessibility of a neutral fraction for laser ionization is shown to be restricted to the nozzle region in the presence of a weak plasma. The survival of this neutral fraction cannot be explained by recombination of the buffer gas alone and perhaps indicates a suppression of the transport of ions due to a plasma-generated electric field. The concept of a competition between the processes that create and destroy the ion of interest is used to explain the different…

Measurement of fission products β decay properties using a total absorption spectrometer

In a nuclear reactor, the decay of fission fragments is at the origin of decay heat and antineutrino flux. These quantities are not well known while they are very important for reactor safety and for our understanding of neutrino physics. One reason for the discrepancies observed in the estimation of the decay heat and antineutrinos flux coming from reactors could be linked with the Pandemonium effect. New measurements have been performed at the JYFL facility of Jyvaskyla with a Total Absorption Spectrometer (TAS) in order to circumvent this effect. An overview of the TAS technique and first results from the 2009 measurement campaign will be presented. © Owned by the authors, published by E…

R-matrix analysis of theβdecays ofN12andB12

The β decays of 12N and 12B have been studied at KVI and JYFL to resolve the composition of the broad and interfering 0+ and 2+ strengths in the triple-α continuum. For the first time a complete treatment of 3α decay is presented including all major breakup channels. A multilevel, many-channel R-matrix formalism has been developed for the complete description of the breakup in combination with the recently published separate analysis of angular correlations. We find that, in addition to the Hoyle state at 7.65 MeV, more than one 0+ and 2+ state is needed to reproduce the spectra. Broad 03+ and 22+ states are found between 10.5 and 12 MeV in this work. The presence of β strength up to the 12…

Ground state properties of manganese isotopes across the N=28 shell closure

Abstract The first optical study of the N = 28 shell closure in manganese is reported. Mean-square charge radii and quadrupole moments, obtained for ground and isomeric states in 50–56 Mn, are extracted using new calculations of atomic factors. The charge radii show a well defined shell closure at the magic number. The behaviour of the charge radii is strikingly different to that of the neutron separation energies where no shell effect can be observed. The nuclear parameters can be successfully described by large scale shell model calculations using the GXPF1A interaction.

Spins and magnetic moments ofMn58,60,62,64ground states and isomers

The odd-odd $^{54,56,58,60,62,64}\mathrm{Mn}$ isotopes ($Z=25$) were studied using bunched-beam collinear laser spectroscopy at ISOLDE, CERN. From the measured hyperfine spectra the spins and magnetic moments of Mn isotopes up to $N=39$ were extracted. The previous tentative ground state spin assignments of $^{58,60,62,64}\mathrm{Mn}$ are now firmly determined to be $I=1$ along with an $I=4$ assignment for the isomeric states in $^{58,60,62}\mathrm{Mn}$. The $I=1$ magnetic moments show a decreasing trend with increasing neutron number while the $I=4$ moments remain quite constant between $N=33$ and $N=37$. The results are compared to large-scale shell-model calculations using the GXPF1A and…

First spatial separation of a heavy ion isomeric beam with a multiple-reflection time-of-flight mass spectrometer

Physics letters / B 744, 137 - 141 (2015). doi:10.1016/j.physletb.2015.03.047

Measurement of fission yields and isomeric yield ratios at IGISOL

Data on fission yields and isomeric yield ratios (IYR) are tools to study the fission process, in particular the generation of angular momentum. We use the IGISOL facility with the Penning trap JYFLTRAP in Jyväskylä, Finland, for such measurements on 232Th and natU targets. Previously published fission yield data from IGISOL concern the 232Th(p,f) and 238U(p,f) reactions at 25 and 50 MeV. Recently, a neutron source, using the Be(p,n) reaction, has been developed, installed and tested. We summarize the results for (p,f) focusing on the first measurement of IYR by direct ion counting. We also present first results for IYR and relative yields for Sn and Sb isotopes in the 128-133 mass range fr…

Exploring the mass surface near the rare-earth abundance peak via precision mass measurements at JYFLTRAP

The JYFLTRAP double Penning trap at the Ion Guide Isotope Separator On-Line (IGISOL) facility has been used to measure the atomic masses of 13 neutron-rich rare-earth isotopes. Eight of the nuclides, $^{161}$Pm, $^{163}$Sm, $^{164,165}$Eu, $^{167}$Gd, and $^{165,167,168}$Tb, were measured for the first time. The systematics of the mass surface has been studied via one- and two-neutron separation energies as well as neutron pairing-gap and shell-gap energies. The proton-neutron pairing strength has also been investigated. The impact of the new mass values on the astrophysical rapid neutron capture process has been studied. The calculated abundance distribution results in a better agreement w…

β-decay data requirements for reactor decay heat calculations: study of the possible source of the gamma-ray discrepancy in reactor heat summation calculations

The decay heat of fission products plays an important role in predictions of the heat up of nuclear fuel in reactors. The released energy is calculated as the summation of the activities of allfission products P(t) = Ei λi Ni(t), where Ei is the decay energy of nuclide i (gamma and beta component), λi is the decay constant of nuclide i and Ni(t) is the number of nuclide i at cooling time t. Even though the reproduction of the measured decay heat has improved in recent years, there is still a long standing discrepancy in the t ∼ 1000s cooling time for some fuels. A possible explanation to this improper description has been found in the work of Yoshida et al. (1), where it has been shown that…

A facility for production and laser cooling of cesium isotopes and isomers

We report on the design, installation, and test of an experimental facility for the production of ultra-cold atomic isotopes and isomers of cesium. The setup covers a broad span of mass numbers and nuclear isomers, allowing one to directly compare chains of isotopes and isotope/isomer pairs. Cesium nuclei are produced by fission or fusion-evaporation reactions using primary proton beams from a 130 MeV cyclotron impinging upon a suitable target. The species of interest is ejected from the target in ionic form, electrostatically accelerated, mass separated, and routed to a science chamber. Here, ions are neutralized by implantation in a thin foil, and extracted by thermal diffusion. A neutral…

First Offline Results from the S3 Low-Energy Branch

International audience; We present the first results obtained from the S3 Low-Energy Branch , the gas cell setup at SPIRAL2-GANIL, which will be installed behind the S3 spectrometer for atomic and nuclear spectroscopy studies of exotic nuclei. The installation is currently being commissioned offline, with the aim to establish optimum conditions for the operation of the radio frequency quadrupole ion guides, mass separation and ion bunching, providing high-efficiency and low-energy spatial spread for the isotopes of interest. Transmission and mass-resolving power measurements are presented for the different components of the S3-LEB setup. In addition, a single-longitudinal-mode, injection-lo…

Characterization of a pulsed injection-locked Ti:sapphire laser and its application to high resolution resonance ionization spectroscopy of copper

A high repetition rate pulsed Ti:sapphire laser injection-locked to a continuous wave seed source is presented. A spectral linewidth of 20 MHz at an average output power of 4W is demonstrated. An enhanced tuning range from 710-920 nm with a single broadband mirror set is realized by the inclusion of a single thin birefringent quartz plate for suppression of unseeded emission. The spectral properties have been analyzed using both a scanning Fabry-P´erot interferometer as well as crossed beam resonance ionization spectroscopy of the hyperfine levels of natural copper. Delayed ionization of the long-lived excited state is demonstrated for increased resolution. For the excited state hyperfine c…

Independent isotopic yields in 25 MeV and 50 MeV proton-induced fission of natU

Independent isotopic yields for elements from Zn to La in the 25 MeV proton-induced fission of natUnatU were determined with the JYFLTRAP facility. In addition, isotopic yields for Zn, Ga, Rb, Sr, Zr, Pd and Xe in the 50 MeV proton-induced fission of natUnatU were measured. The deduced isotopic yield distributions are compared with a Rubchenya model, the GEF model with universal parameters and the semi-empirical Wahl model. Of these, the Rubchenya model gives the best overall agreement with the obtained data. Combining the isotopic yield data with mass yield data to obtain the absolute independent yields was attempted. The result depends on the mass yield distribution. peerReviewed

Off-line studies of the laser ionization of yttrium at the IGISOL facility

A laser ion source is under development at the IGISOL facility, Jyvaskyla, in order to address deficiencies in the ion guide technique. The key elements of interest are those of a refractory nature, whose isotopes and isomers are widely studied using both laser spectroscopic and high precision mass measurement techniques. Yttrium has been the first element of choice for the new laser ion source. In this work we present a new coupled dye-Ti:Sapphire laser scheme and give a detailed discussion of the results obtained from laser ionization of yttrium atoms produced in an ion guide via joule heating of a filament. The importance of not only gas purity, but indeed the baseline vacuum pressure in…

Nuclear spin determination of100mY by collinear laser spectroscopy of optically pumped ions

The nuclear spin of the τ1/2 = 0.94 s isomer in 100Y has been determined by collinear laser spectroscopy of optically pumped yttrium fission fragments at the IGISOL facility, JYFL. The isotopes 96, 98, 99, 100Y were produced by the proton-induced fission of natural uranium, and studied on the 4d5s 3D2 (1045 cm−1) → 4d5p 3P1 (32 124 cm−1) transition at 321.67 nm. Enhancement of the population of the metastable 3D2 level was achieved by optically pumping the ground state population via the 5s2 1S0 → 4d5p 1P1 transition at 363.31 nm while the ions were stored in a linear Paul trap. These data, when combined with previous spectroscopic results, give sufficient information for the nuclear spin o…

Total Absorption Spectroscopy of Fission Fragments Relevant for Reactor Antineutrino Spectra and Decay Heat Calculations

Beta decay of fission products is at the origin of decay heat and antineutrino emission in nuclear reactors. Decay heat represents about 7% of the reactor power during operation and strongly impacts reactor safety. Reactor antineutrino detection is used in several fundamental neutrino physics experiments and it can also be used for reactor monitoring and non-proliferation purposes. 92,93Rb are two fission products of importance in reactor antineutrino spectra and decay heat, but their β-decay properties are not well known. New measurements of 92,93Rb β-decay properties have been performed at the IGISOL facility (Jyväskylä, Finland) using Total Absorption Spectroscopy (TAS). TAS is complemen…

Structure of115Ag studied byβ−decays of115Pd and115Pdm

The excited levels of ${}^{115}$Ag have been studied via the beta decay of ${}^{115}$Pd and ${}^{115}$Pd${}^{m}$. The beta-decay schemes for both states have been considerably extended, especially the scheme following the decay of ${}^{115}$Pd${}^{m}$ which was practically unknown before this work. Transition intensities and ${\mathrm{log}}_{10}ft$ values are reported, which have been missing in the literature. A set of levels around 2 MeV has been found to be strongly populated by the beta decay of the ground state of ${}^{115}$Pd and is suggested to have a three-quasiparticle nature. The properties of excited levels have been compared with the level systematics of lighter neutron-rich sil…

Laser spectroscopy of niobium fission fragments: first use of optical pumping in an ion beam cooler buncher.

A new method of optical pumping in an ion beam cooler buncher has been developed to selectively enhance ionic metastable state populations. The technique permits the study of elements previously inaccessible to laser spectroscopy and has been applied here to the study of Nb. Model independent mean-square charge radii and nuclear moments have been studied for $^{90,90\text{ }\mathrm{m},91,91\text{ }\mathrm{m},92,93,99,101,103}\mathrm{Nb}$ to cover the region of the $N=50$ shell closure and $N\ensuremath{\approx}60$ sudden onset of deformation. The increase in mean-square charge radius is observed to be less than that for Y, with a substantial degree of $\ensuremath{\beta}$ softness observed …

New insights into triaxiality and shape coexistence from odd-mass Rh109

Rapid shape evolutions near A = 100 are now the focus of much attention in nuclear science. Much of the recent work has been centered on isotopes with Z <= 40, where the shapes are observed to transition between near-spherical to highly deformed with only a single pair of neutrons added. At higher Z, the shape transitions become more gradual as triaxiality sets in, yet the coexistence of varying shapes continues to play an important role in the low-energy nuclear structure, particularly in the odd-Z isotopes. This work aims to characterize competing shapes in the triaxial region between Zr and Sn isotopes using ultrafast timing techniques to measure lifetimes of excited states in the neutro…

Determination of the ground-state hyperfine structure in neutral229Th

The ground-state hyperfine structure of neutral 229Th has been measured for the first time using high-resolution resonance ionization spectroscopy. The measurements were performed as a preparatory work aimed at the identification of the predicted low-lying 7.6 eV isomer in 229Th through an investigation of its hyperfine structure. The hyperfine coupling constants have been extracted for the atomic ground state as well as for three excited states at 26 096, 26 113 and 38 278 cm−1. Due to rather small splittings not all hyperfine components were completely resolved and therefore an extensive χ2-error analysis was performed to achieve reliable results. The ground-state transition to the excite…

Isotope shifts from collinear laser spectroscopy of doubly charged yttrium isotopes

Collinear laser spectroscopy has been performed on doubly charged ions of radioactive yttrium in order to study the isotope shifts of the 294.6-nm $5s\phantom{\rule{0.16em}{0ex}}^{2}S_{1/2}\ensuremath{\rightarrow}5p\phantom{\rule{0.16em}{0ex}}^{2}P_{1/2}$ line. The potential of such an alkali-metal-like transition to improve the reliability of atomic-field-shift and mass-shift factor calculations, and hence the extraction of nuclear mean-square radii, is discussed. Production of yttrium ion beams for such studies is available at the IGISOL IV Accelerator Laboratory, Jyv\"askyl\"a, Finland. This newly recommissioned facility is described here in relation to the on-line study of accelerator-p…

A Novel Method for the Measurement of Half-Lives and Decay Branching Ratios of Exotic Nuclei

A novel method for simultaneous measurement of masses, Q-values, isomer excitation energies, half-lives and decay branching ratios of exotic nuclei has been demonstrated. The method includes first use of a stopping cell as an ion trap, combining containment of precursors and decay-recoils for variable durations in a cryogenic stopping cell (CSC), and afterwards the identification and counting of them by a multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS). Feasibility has been established by recording the decay and growth of $^{216}$Po and $^{212}$Pb (alpha decay) and of $^{119m2}$Sb (t$_{1/2}$ = 850$\pm$90 ms) and $^{119g}$Sb (isomer transition), obtaining half-lives and bran…

Excited levels in the multishaped 117Pd nucleus studied via β decay of 117Rh

Monoisotopic samples of exotic, neutron-rich 117Rh nuclei, produced in the proton-induced fission of 238U and separated using the IGISOL mass separator coupled to the JYFLTRAP Penning trap, were used to perform β and γ coincidence spectroscopy of 117Pd. The spin parity of the ground state of 117Pd was determined to be 1/2+ and the 19.1 ms isomer at 203.2 keV was assigned a spin-parity 7/2−. The 117Rh β−-decay scheme was considerably extended, and various sequences of the levels were interpreted as resulting from the prolate, oblate, and triaxial nuclear shapes. Some of the β− decays were considered as the allowed Gamow-Teller transitions. The experimental distribution of Gamow-Teller streng…

Precision mass measurements of neutron-rich yttrium and niobium isotopes

Abstract The atomic masses of neutron-rich 95–101 Y and 101–107 Nb produced in proton-induced fission of uranium were determined using the JYFLTRAP double Penning trap setup. Accuracies of better than 10 keV could be reached for most nuclides. The masses of 106,107 Nb were measured for the first time. The energies of the isomeric states in 96 Y and 100 Y were measured as 1541(10) keV and 145(15) keV. The niobium isotopes appear to be systematically less bound than the values given in the latest Atomic Mass Evaluation. The new data lie in a region of the nuclear chart characterised by the transition from spherical to strongly deformed shapes. These structural changes are explored by studying…

On-Line Ion Cooling and Bunching for Collinear Laser Spectroscopy

A new method has been developed for increasing the sensitivity of collinear laser spectroscopy. The method utilizes an ion-trapping technique in which a continuous low-energy ion beam is cooled and accumulated in a linear Paul trap and subsequently released as a short ( $10--20\ensuremath{\mu}\mathrm{s}$) bunch. In collinear laser measurements the signal-to-noise ratio has been improved by a factor of $2\ifmmode\times\else\texttimes\fi{}{10}^{4}$, allowing spectroscopic measurements to be made with ion-beam fluxes of $\ensuremath{\sim}50\mathrm{ions}{\mathrm{s}}^{\ensuremath{-}1}$. The bunching method has been demonstrated in an on-line isotope shift and hyperfine structure measurement on r…

Towards high-resolution laser ionization spectroscopy of the heaviest elements in supersonic gas jet expansion

Resonant laser ionization and spectroscopy are widely used techniques at radioactive ion beam facilities to produce pure beams of exotic nuclei and measure the shape, size, spin and electromagnetic multipole moments of these nuclei. However, in such measurements it is difficult to combine a high efficiency with a high spectral resolution. Here we demonstrate the on-line application of atomic laser ionization spectroscopy in a supersonic gas jet, a technique suited for high-precision studies of the ground- and isomeric-state properties of nuclei located at the extremes of stability. The technique is characterized in a measurement on actinium isotopes around the N=126 neutron shell closure. A…

Measurements of isomeric yield ratios of fission products from proton-induced fission on natU and 232Th via direct ion counting

Independent isomeric yield ratios (IYR) of 81Ge, 96Y, 97Y, 97Nb, 128Sn and 130Sn have been determined in the 25 MeV proton-induced fission of natU and 232Th. The measurements were performed at the Ion Guide Isotope Separator On-Line (IGISOL) facility at the University of Jyväskylä. A direct ion counting measurement of the isomeric fission yield ratios was accomplished for the first time, registering the fission products in less than a second after their production. In addition, the IYRs of natU were measured by means of γ-spectroscopy in order to verify the consistency of the recently upgraded experimental setup. From the obtained results, indications of a dependence of the production rate …

Penning-trap-assisted study of 115Ru beta decay

The beta decay of 115Ru has been studied by means of Penning-trap-assisted beta and gamma spectroscopy at the IGISOL facility. The level scheme of 115Rh has been substantially extended and compared with the level systematics of lighter rhodium isotopes. Tentative candidates for three states of the deformed K = 1/2 band have been suggested. The beta-strength distribution of the beta decay of 115Ru differs from the beta decays of 111, 113, 113mRu isotopes due to non-observation of the 3-quasiparticle states in 115Rh. The decay properties of 115Ru indicate a spin-parity of (3/2+ for its beta-decaying ground state. In addition, possible Nilsson states as well as the shape and spin transitions i…

Mass and half-life measurements of neutron-deficient iodine isotopes

The European physical journal / A 56(5), 143 (2020). doi:10.1140/epja/s10050-020-00153-5

Mass Measurements for the rp Process

One of the key parameters for the reaction network calculations for the rapid proton capture (rp) process, occurring e.g., in type I X-ray bursts, are the masses of the involved nuclei. Nowadays, masses of even rather exotic nuclei can be measured very precisely employing Penning-trap mass spectrometry. With the JYFLTRAP Penning trap at the IGISOL facility, masses of around 100 neutron-deficient nuclei have been determined with a typical precision of a few keV. Most recently, 25Al, 30P, 31Cl, and 52Co have been measured. Of these, the precision of the mass-excess value of 31Cl was improved from 50 to 3.4 keV, and the mass of 52Co was experimentally determined for the first time. The mass of…

Total Absorption Study of Beta Decays Relevant for Nuclear Applications and Nuclear Structure

Abstract An overview is given of our activities related to the study of the beta decay of neutron rich nuclei relevant for nuclear applications. Recent results of the study of the beta decay of 87,88 Br using a new segmented total absorption spectrometer are presented. The measurements were performed at the IGISOL facility using trap-assisted total absorption spectroscopy.

Electron capture on 116In and implications for nuclear structure related to double-\beta decay

The electron capture decay branch of 116In has been measured to be [2.46 ± 0.44(stat.) ± 0.39(syst.)] × 10−4 using Penning trap-assisted decay spectroscopy. The corresponding Gamow-Teller transition strength is shown to be compatible with the most recent value extracted from the (p, n) charge-exchange reaction, providing a resolution to longstanding discrepancies. This transition can now be used as a reliable benchmark for nuclearstructure calculations of the matrix element for the neutrinoless double-β decay of 116Cd and other nuclides. peerReviewed

Mass Measurements and Implications for the Energy of the High-Spin Isomer inAg94

Nuclides in the vicinity of {sup 94}Ag have been studied with the Penning trap mass spectrometer JYFLTRAP at the Ion-Guide Isotope Separator On-Line. The masses of the two-proton-decay daughter {sup 92}Rh and the beta-decay daughter {sup 94}Pd of the high-spin isomer in {sup 94}Ag have been measured, and the masses of {sup 93}Pd and {sup 94}Ag have been deduced. When combined with the data from the one-proton- or two-proton-decay experiments, the results lead to contradictory mass excess values for the high-spin isomer in {sup 94}Ag, -46 370(170) or -44 970(100) keV, corresponding to excitation energies of 6960(400) or 8360(370) keV, respectively.

Excited states inPd115populated in theβ−decay ofRh115

Excited states in $^{115}\mathrm{Pd}$, populated following the ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay of $^{115}\mathrm{Rh}$ have been studied by means of $\ensuremath{\gamma}$ spectroscopy after the Penning-trap station at the IGISOL facility, University of Jyv\"askyl\"a. The $1$$/$$2$${}^{+}$ spin and parity assignment of the ground state of $^{115}\mathrm{Pd}$, confirmed in this work, may indicate a transition to an oblate shape in Pd isotopes at high neutron number.

Development of a low-energy radioactive ion beam facility for the MARA separator

A low-energy radioactive ion beam facility for the production and study of nuclei produced close to the proton drip line is under development at the Accelerator Laboratory of the University of Jyv\"askyl\"a, Finland. The facility will take advantage of the mass selectivity of the recently commissioned MARA vacuum-mode mass separator. The ions selected by MARA will be stopped and thermalised in a small-volume gas cell prior to extraction and further mass separation. The gas cell design allows for resonance laser ionisation/spectroscopy both in-gas-cell and in-gas-jet. The facility will include experimental setups allowing ion counting, mass measurement and decay spectroscopy.

The β-decay approach for studying 12C

6 pags., 3 figs. -- 9th International Conference on Clustering Aspects of Nuclear Structure and Dynamics (CLUSTERS'07) 3–7 September 2007, Stratford upon Avon, UK

Shape coexistence in the odd-odd nucleus 98Y : the role of the g9/2 neutron extruder

Excited states in 98Y, populated in neutron-induced fission of 235U and in spontaneous fission of 248Cm and 252Cf, have been studied by means of γ spectroscopy using the Lohengrin fission-fragment separator at ILL Grenoble and the EXILL, Eurogam2, and Gammasphere Ge arrays. Two new isomers have been found in 98Y: a deformed one with T1/2 = 180(7) ns and a rotational band on top of it, and a spherical one with T1/2 = 0.45(15)μs, analogous to the 8+ isomer in 96Y, corresponding to the (νg7/2,πg9/2)8+ spherical configuration. Using the JYFLTRAP Penning trap, an accurate excitation energy of 465.7(7) keV has been determined for the 2.36-s isomer in 98Y. This result and the studies of excited le…

A new off-line ion source facility at IGISOL

An off-line ion source station has been commissioned at the IGISOL (Ion Guide Isotope Separator On-Line) facility. It offers the infrastructure needed to produce stable ion beams from three off-line ion sources in parallel with the radioactive ion beams produced from the IGISOL target chamber. This has resulted in improved feasibility for new experiments by offering reference ions for Penning-trap mass measurements, laser spectroscopy and atom trap experiments.

Reactor Decay Heat inPu239: Solving theγDiscrepancy in the 4–3000-s Cooling Period

The {beta} feeding probability of {sup 102,104,105,106,107}Tc, {sup 105}Mo, and {sup 101}Nb nuclei, which are important contributors to the decay heat in nuclear reactors, has been measured using the total absorption technique. We have coupled for the first time a total absorption spectrometer to a Penning trap in order to obtain sources of very high isobaric purity. Our results solve a significant part of a long-standing discrepancy in the {gamma} component of the decay heat for {sup 239}Pu in the 4-3000 s range.

New Beta-delayed Neutron Measurements in the Light-mass Fission Group

A new accurate determination of beta-delayed neutron emission probabilities from nuclei in the low mass region of the light fission group has been performed. The measurements were carried out using the BELEN 4π neutron counter at the IGISOL-JYFL mass separator in combination with a Penning trap. The new results significantly improve the uncertainties of neutron emission probabilities for {sup 91}Br, {sup 86}As, {sup 85}As, and {sup 85}Ge nuclei.

Decay study ofTc114with a Penning trap

The level structure of $^{114}\mathrm{Ru}$ has been investigated via the $\ensuremath{\beta}$ decay of very neutron-rich $^{114}\mathrm{Tc}$ by means of Penning-trap-assisted $\ensuremath{\gamma}$ spectroscopy. The deduced $\ensuremath{\beta}$-decay scheme suggests the existence of two $\ensuremath{\beta}$-decaying states in $^{114}\mathrm{Tc}$ with ${I}^{\ensuremath{\pi}}={1}^{+}$ and $I\ensuremath{\geqslant}$ 4, with half-lives of ${t}_{1/2}({1}^{+})=90(20)$ ms and ${t}_{1/2}(I\ensuremath{\geqslant}4)=100(20)$ ms, respectively. The ${Q}_{\ensuremath{\beta}}$ value, which covers a possible mixture of two states, has been determined to be ${Q}_{\ensuremath{\beta}}=11 785(12)$ keV. The level…

High-precision mass measurements and production of neutron-deficient isotopes using heavy-ion beams at IGISOL

An upgraded ion-guide system for the production of neutron-deficient isotopes with heavy-ion beams has been commissioned at the IGISOL facility with an $^{36}\mathrm{Ar}$ beam on a $^{\mathrm{nat}}\mathrm{Ni}$ target. It was used together with the JYFLTRAP double Penning trap to measure the masses of $^{82}\mathrm{Zr}, ^{84}\mathrm{Nb}, ^{86}\mathrm{Mo}, ^{88}\mathrm{Tc}$, and $^{89}\mathrm{Ru}$ ground states and the isomeric state $^{88}\mathrm{Tc}^{m}$. Of these, $^{89}\mathrm{Ru}$ and $^{88}\mathrm{Tc}^{m}$ were measured for the first time. The precision of measurements of $^{82}\mathrm{Zr}, ^{84}\mathrm{Nb}$, and $^{88}\mathrm{Tc}$ was significantly improved. The literature value for $^…

QValues of the SuperallowedβEmittersAlm26,Sc42, andV46and Their Impact onVudand the Unitarity of the Cabibbo-Kobayashi-Maskawa Matrix

The $\ensuremath{\beta}$-decay ${Q}_{\mathrm{EC}}$ values of the superallowed beta emitters $^{26}\mathrm{Al}^{m}$, $^{42}\mathrm{Sc}$, and $^{46}\mathrm{V}$ have been measured with a Penning trap to a relative precision of better than $8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$. Our result for $^{46}\mathrm{V}$, 7052.72(31) keV, confirms a recent measurement that differed from the previously accepted reaction-based ${Q}_{\mathrm{EC}}$ value. However, our results for $^{26}\mathrm{Al}^{m}$ and $^{42}\mathrm{Sc}$, 4232.83(13) keV and 6426.13(21) keV, are consistent with previous reaction-based values. By eliminating the possibility of a systematic difference between the two t…

Fission studies at IGISOL/JYFLTRAP: Simulations of the ion guide for neutron-induced fission and comparison with experimental data

For the production of exotic nuclei at the IGISOL facility, an ion guide for neutron-induced fission has been developed and tested in experiments. Fission fragments are produced inside the ion guide and collected using a helium buffer gas. Meanwhile, a GEANT4 model has been developed to simulate the transportation and stopping of the charged fission products. In a recent measurement of neutron-induced fission yields, implantation foils were located at different positions in the ion guide. The gamma spectra from these foils and the fission targets are compared to the results from the GEANT4 simulation. In order to allow fission yield measurements in the low yield regions, towards the tails a…

Quenching of the SnSbTe Cycle in the rp-Process

First β -decay scheme of Nb107 : New insight into the low-energy levels of Mo107

Monoisotopic samples of $^{107}\mathrm{Nb}$ nuclei, produced in the proton-induced fission of $^{238}\mathrm{U}$ and separated using the IGISOL mass separator coupled to a Penning trap, were used to perform $\ensuremath{\beta}$- and $\ensuremath{\gamma}$-coincidence spectroscopy of $^{107}\mathrm{Mo}$. Gamma transitions and excited levels in $^{107}\mathrm{Mo}$ were observed in $\ensuremath{\beta}$ decay for the first time. Spin and parity $1/{2}^{+}$ for the ground state of $^{107}\mathrm{Mo}$ is proposed, to replace the previous $5/{2}^{+}$ assignment. The experimental $\ensuremath{\beta}$-decay half-life of $^{107}\mathrm{Nb}$ was estimated to be $0.27\ifmmode\pm\else\textpm\fi{}0.02$ s.

Performance of a high repetition pulse rate laser system for in-gas-jet laser ionization studies with the Leuven laser ion source @ LISOL

The Leuven Isotope Separator On-Line (LISOL) facility at the Cyclotron Research Center (CRC) Louvain-la-Neuve; The laser ionization efficiency of the Leuven gas cell-based laser ion source was investigated under on- and off-line conditions using two distinctly different laser setups: a low-repetition rate dye laser system and a high-repetition rate Ti:sapphire laser system. A systematic study of the ion signal dependence on repetition rate and laser pulse energy was performed in off-line tests using stable cobalt and copper isotopes. These studies also included in-gas-jet laser spectroscopy measurements on the hyperfine structure of 63Cu. A final run under on-line conditions in which the ra…

First evidence of multiple β-delayed neutron emission for isotopes with a > 100

The β-delayed neutron emission probability, Pn, of very neutron-rich nuclei allows us to achieve a better understanding of the nuclear structure above the neutron separation energy, Sn. The emission of neutrons can become the dominant decay process in neutron-rich astrophysical phenomena such as the rapid neutron capture process (r-process). There are around 600 accessible isotopes for which β-delayed one-neutron emission (β1n) is energetically allowed, but the branching ratio has only been determined for about one third of them. β1n decays have been experimentally measured up to the mass A ∼ 150, plus a single measurement of 210Tl. Concerning two-neutron emitters (β2n), ∼ 300 isotopes are …

On the decrease in charge radii of multi-quasi particle isomers

Abstract We report changes in mean-square charge radii, δ 〈 r 2 〉 , magnetic moments and quadrupole moments for three multi-quasi particle isomers; 97m2Y, 176mYb and 178m1Hf. All the isomers are observed to display a decrease in 〈 r 2 〉 compared to the lower-lying nuclear state on which the isomer is built. The decreases in 〈 r 2 〉 occur despite the isomers showing increases in quadrupole moment. Possible mechanisms for the effect, which is now seen for six multi-quasi particle isomers, are discussed.

Developments towards in-gas-jet laser spectroscopy studies of actinium isotopes at LISOL

To study exotic nuclides at the borders of stability with laser ionization and spectroscopy techniques, highest efficiencies in combination with a high spectral resolution are required. These usually opposing requirements are reconciled by applying the in-gas-laser ionization and spectroscopy (IGLIS) technique in the supersonic gas jet produced by a de Laval nozzle installed at the exit of the stopping gas cell. Carrying out laser ionization in the low-temperature and low density supersonic gas jet eliminates pressure broadening, which will significantly improve the spectral resolution. This article presents the required modifications at the Leuven Isotope Separator On-Line (LISOL) facility…

Internal conversion from excited electronic states of 229Th ions

The process of internal conversion from excited electronic states is investigated theoretically for the case of the vacuum-ultraviolet nuclear transition of 229 Th . Due to the very low transition energy, the 229 Th nucleus offers the unique possibility to open the otherwise forbidden internal conversion nuclear decay channel for thorium ions via optical laser excitation of the electronic shell. We show that this feature can be exploited to investigate the isomeric state properties via observation of internal conversion from excited electronic configurations of Th + and Th 2 + ions. A possible experimental realization of the proposed scenario at the nuclear laser spectroscopy facility IGISO…

High-resolution laser spectroscopy of long-lived plutonium isotopes

Long-lived isotopes of plutonium were studied using two complementary techniques, high-resolution resonance ionisation spectroscopy (HR-RIS) and collinear laser spectroscopy (CLS). Isotope shifts have been measured on the $5f^67s^2\ ^7F_0 \rightarrow 5f^56d^27s\ (J=1)$ and $5f^67s^2\ ^7F_1 \rightarrow 5f^67s7p\ (J=2)$ atomic transitions using the HR-RIS method and the hyperfine factors have been extracted for the odd mass nuclei $^{239,241}$Pu. Collinear laser spectroscopy was performed on the $5f^67s\ ^8F_{1/2} \rightarrow J=1/2\; (27523.61\text{cm}^{-1})$ ionic transition with the hyperfine $A$ factors measured for $^{239}$Pu. Changes in mean-squared charge radii have been extracted and s…

Total Absorption Spectroscopy of Fission Fragments Relevant for Reactor Antineutrino Spectra Determination

8 pags., 3 figs., 1 tab. ; Presented at the XXXIV Mazurian Lakes Conference on Physics, Piaski, Poland, September 6–13, 2015.

Precision Mass Measurements beyondSn132: Anomalous Behavior of Odd-Even Staggering of Binding Energies

Atomic masses of the neutron-rich isotopes $^{121--128}\mathrm{Cd}$, $^{129,131}\mathrm{In}$, $^{130--135}\mathrm{Sn}$, $^{131--136}\mathrm{Sb}$, and $^{132--140}\mathrm{Te}$ have been measured with high precision (10 ppb) using the Penning-trap mass spectrometer JYFLTRAP. Among these, the masses of four $r$-process nuclei $^{135}\mathrm{Sn}$, $^{136}\mathrm{Sb}$, and $^{139,140}\mathrm{Te}$ were measured for the first time. An empirical neutron pairing gap expressed as the odd-even staggering of isotopic masses shows a strong quenching across $N=82$ for Sn, with a $Z$ dependence that is unexplainable by the current theoretical models.

Total absorption γ -ray spectroscopy of the β -delayed neutron emitters Br87 , Br88 , and Rb94

We investigate the decay of 87,88Br and 94Rb using total absorption γ -ray spectroscopy. These important fission products are β-delayed neutron emitters. Our data show considerable βγ intensity, so far unobserved in high-resolution γ -ray spectroscopy, from states at high excitation energy. We also find significant differences with the β intensity that can be deduced from existing measurements of the β spectrum. We evaluate the impact of the present data on reactor decay heat using summation calculations. Although the effect is relatively small it helps to reduce the discrepancy between calculations and integral measurements of the photon component for 235U fission at cooling times in the r…

Removal of molecular contamination in low-energy RIBs by the isolation-dissociation-isolation method

Nuclear instruments &amp; methods in physics research / B 463, 324 - 326 (2020). doi:10.1016/j.nimb.2019.04.072

The decay of 133mXe.

The decay of (133m)Xe has been re-measured using an electron-transporter spectrometer and a planar HPGe detector. The sample of (133m)Xe was produced by means of proton-induced fission using an ion-guide based on-line mass separator. The deduced K and L+M+... shell conversion coefficients, alpha(Kappa)=6.5(9) and alpha(L+M+...)=2.9(4), agree within the uncertainty limits with the theoretical values and remove the inconsistencies between the previous experimental studies of (133m)Xe.

New lifetime measurements in 109 Pd and the onset of deformation at N = 60

Several new subnanosecond lifetimes were measured in 109Pd using the fast-timing βγγ (t) method. Fission fragments of the A = 109 mass chain were produced by bombarding natural uranium with 30 MeV protons at the Jyvaskyl ¨ a Ion Guide Isotope Separator On-Line (IGISOL) facility. Lifetimes were obtained for excited states ¨ in 109Pd populated following β decay of 109Rh. The new lifetimes provide some insight into the evolution of nuclear structure in this mass region. In particular, the distinct structure of the two low-lying 7/2+ states occurring systematically across the Pd isotopic chain is supported by the new lifetime measurements. The available nuclear data indicate a sudden increase i…

Systematic studies of the accuracy of the Penning trap mass spectrometer JYFLTRAP

Abstract Measurements to quantify the mass-dependent systematic effect and the residual uncertainty of the JYFLTRAP setup have been performed with carbon-cluster ions. The primary quantities reported in this work are a mass-dependent uncertainty of σ m ( r ) / r = ( 7.8 ± 0.3 × 10 - 10 / u ) × Δ m and a residual uncertainty of σ res ( r ) / r = 1.2 × 10 - 8 for the JYFLTRAP mass spectrometer. By restricting the mass difference between the reference ion and ion of interest to | m meas - m ref | ≤ 24 , the values for the mass-dependent effect and the corresponding residual uncertainty are σ m , lim ( r ) / r = ( 7.5 ± 0.4 × 10 - 10 / u ) × Δ m and σ res , lim ( r ) / r = 7.9 × 10 - 9 , respec…

Precise branching ratios to unbound 12C states from 12N and 12B β-decays

6 pages, 2 tables, 4 figures.--PACS nrs.: 21.45.-v; 23.40.-s; 27.20.+n; 21.60.De.--Printed version published Aug 3, 2009

In-gas-cell laser ionization studies of plutonium isotopes at IGISOL

Abstract In-gas-cell resonance laser ionization has been performed on long-lived isotopes of Pu at the IGISOL facility, Jyvaskyla. This initiates a new programme of research towards high-resolution optical spectroscopy of heavy actinide elements which can be produced in sufficient quantities at research reactors and transported to facilities elsewhere. In this work a new gas cell has been constructed for fast extraction of laser-ionized elements. Samples of 238–240,242 Pu and 244 Pu have been evaporated from Ta filaments, laser ionized, mass separated and delivered to the collinear laser spectroscopy station. Here we report on the performance of the gas cell through studies of the mass spec…

r Process (n, γ) Rate Constraints from the γ Emission of Neutron Unbound States in β decay

Total absorption gamma-ray spectroscopy is used to measure accurately the intensity of γγ emission from neutron-unbound states populated in the ββ-decay of delayed-neutron emitters. From the comparison of this intensity with the intensity of neutron emission a constraint on the (n, γγ) cross section for highly unstable neutron-rich nuclei can be deduced. A surprisingly large γγ branching was observed for a number of isotopes which might indicate the need to increase by a large factor the Hauser-Feshbach (n, γγ) cross-section estimates that impact on r process abundance calculations. peerReviewed

Total Absorption Spectroscopy Study ofRb92Decay: A Major Contributor to Reactor Antineutrino Spectrum Shape

The antineutrino spectra measured in recent experiments at reactors are inconsistent with calculations based on the conversion of integral beta spectra recorded at the ILL reactor. (92)Rb makes the dominant contribution to the reactor antineutrino spectrum in the 5-8 MeV range but its decay properties are in question. We have studied (92)Rb decay with total absorption spectroscopy. Previously unobserved beta feeding was seen in the 4.5-5.5 region and the GS to GS feeding was found to be 87.5(25)%. The impact on the reactor antineutrino spectra calculated with the summation method is shown and discussed.

Mass of astrophysically relevantCl31and the breakdown of the isobaric multiplet mass equation

The mass of $^{31}\mathrm{Cl}$ has been measured with the JYFLTRAP double-Penning-trap mass spectrometer at the Ion Guide Isotope Separator On-Line (IGISOL) facility. The determined mass-excess value, $\ensuremath{-}7034.7(34)$ keV, is 15 times more precise than in the Atomic Mass Evaluation 2012. The quadratic form of the isobaric multiplet mass equation for the $T=3/2$ quartet at $A=31$ fails $({\ensuremath{\chi}}_{n}^{2}=11.6)$ and a nonzero cubic term, $d=\ensuremath{-}3.5(11)$ keV, is obtained when the new mass value is adopted. $^{31}\mathrm{Cl}$ has been found to be less proton-bound, with a proton separation energy of ${S}_{p}=264.6(34)$ keV. Energies for the excited states in $^{31…

In-gas laser ionization and spectroscopy of actinium isotopes near the N=126 closed shell

The in-gas laser ionization and spectroscopy (IGLIS) techniquewas applied on the $^{212–215}$Ac isotopes, produced at the Leuven Isotope Separator On-Line (LISOL) facility by using the in-gas-cell and the in-gas-jet methods. The first application under on-line conditions of the in-gas-jet laser spectroscopy method showed a superior performance in terms of selectivity, spectral resolution, and efficiency in comparison with the in-gas-cell method. Following the analysis of both experiments, the magnetic-dipole moments for the $^{212–215}$Ac isotopes, electric-quadrupole moments and nuclear spins for the $^{214,215}$Ac isotopes are presented and discussed. A good agreement is obtained with lar…

Recent mass measurements for the r process at JYFLTRAP

Changes in nuclear structure along the Mn isotopic chain studied via charge radii

The hyperfine spectra of $^{51,53-64}$Mn were measured in two experimental runs using collinear laser spectroscopy at ISOLDE, CERN. Laser spectroscopy was performed on the atomic $3d^5\ 4s^2\ ^{6}\text{S}_{5/2}\rightarrow 3d^5\ 4s4p\ ^{6}\text{P}_{3/2}$ and ionic $3d^5\ 4s\ ^{5}\text{S}_2 \rightarrow 3d^5\ 4p\ ^{5}\text{P}_3$ transitions, yielding two sets of isotope shifts. The mass and field shift factors for both transitions have been calculated in the multiconfiguration Dirac-Fock framework and were combined with a King plot analysis in order to obtain a consistent set of mean-square charge radii which, together with earlier work on neutron-deficient Mn, allow the study of nuclear struc…

Mass Measurements for the rp Process

Excited levels in the multishaped Pd117 nucleus studied via β decay of Rh117

Monoisotopic samples of exotic, neutron-rich $^{117}\mathrm{Rh}$ nuclei, produced in the proton-induced fission of $^{238}\mathrm{U}$ and separated using the IGISOL mass separator coupled to the JYFLTRAP Penning trap, were used to perform $\ensuremath{\beta}$ and $\ensuremath{\gamma}$ coincidence spectroscopy of $^{117}\mathrm{Pd}$. The spin parity of the ground state of $^{117}\mathrm{Pd}$ was determined to be $1/{2}^{+}$ and the 19.1 ms isomer at 203.2 keV was assigned a spin-parity $7/{2}^{\ensuremath{-}}$. The $^{117}\mathrm{Rh}$ ${\ensuremath{\beta}}^{\ensuremath{-}}$-decay scheme was considerably extended, and various sequences of the levels were interpreted as resulting from the prol…

Summation Calculations for Reactor Antineutrino Spectra, Decay Heat and Delayed Neutron Fractions Involving New TAGS Data and Evaluated Databases

9 pags., 3 figs. -- Open Access funded by Creative Commons Atribution Licence 4.0

First experimental results of a cryogenic stopping cell with short-lived, heavy uranium fragments produced at 1000 MeV/u

A cryogenic stopping cell (CSC) has been commissioned with U-238 projectile fragments produced at 1000 MeV/u. The spatial isotopic separation in flight was performed with the FRS applying a monoenergetic degrader. For the first time, a stopping cell was operated with exotic nuclei at cryogenic temperatures (70 to 100K). A helium stopping gas density of up to 0.05mg/cm(3) was used, about two times higher than reached before for a stopping cell with RF ion repelling structures. An overall efficiency of up to 15%, a combined ion survival and extraction efficiency of about 50%, and extraction times of 24ms were achieved for heavy a-decaying uranium fragments. Mass spectrometry with a multiple-r…

A sextupole ion beam guide to improve the efficiency and beam quality at IGISOL

The laser ion source project at the IGISOL facility, Jyvaskyla, has motivated the development and construction of an rf sextupole ion beam guide (SPIG) to replace the original skimmer electrode. The SPIG has been tested both off-line and on-line in proton-induced fission, light-ion and heavy-ion induced fusion-evaporation reactions and, in each case, has been directly compared to the skimmer system. For both fission and light-ion induced fusion, the SPIG has improved the mass-separated ion yields by a factor of typically 4 to 8. Correspondingly, the transmission efficiency of both systems has been studied in simulations with and without space charge effects. The transport capacity of the SP…

Improvements on Decay Heat Summation Calculations by Means of Total Absorption Gamma-ray Spectroscopy Measurements

The decay heat of fission products plays an important role in predictions of the heat released by nuclear fuel in reactors. In this contribution we present results of the analysis of the measurement of the beta decay of some refractory isotopes that were considered possible important contributors to the decay heat in reactors. The measurements presented here were performed at the IGISOL facility of the University of Jyvaeskylae, Finland. In our measurements we have combined for the first time a Penning trap (JYFLTRAP), which was used as a high resolution isobaric separator, with a total absorption spectrometer. The results of the measurements as well as their consequences for decay heat sum…

Nuclear charge radii of neutron deficient titanium isotopes44Ti and45Ti

Optical isotope shifts of the unstable 44,45Ti isotopes, as well as those of stable 46−50Ti, have been investigated by collinear laser spectroscopy on fast ion beams using an ion guide isotope separator with a cooler-buncher. Changes in mean square charge radii across the neutron 1f7/2 shell are deduced. The evolution of the even-N Ti nuclear radii shows a generally increasing tendency with decreasing neutron number. This behaviour is significantly different to that of the neighbouring Ca isotopes which exhibit a symmetric parabolic behaviour across the shell. The trend of the Ti nuclear radii is consistent with the predictions of the relativistic mean-field theory. The charge radius of 44T…

β-decay ofO13

The beta decay of O-13 has been studied at the IGISOL facility of the Jyvaskyla accelerator centre (Finland). By developing a low-energy isotope-separated beam of O-13 and using a modern segmented charged-particle detector array an improved measurement of the delayed proton spectrum was possible. Protons with energy up to more than 12 MeV are measured and the corresponding log(ft) values extracted. A revised decay scheme is constructed. The connection to molecular states and the shell model is discussed.

Production of Sn and Sb isotopes in high-energy neutron induced fission of natU

The first systematic measurement of neutron-induced fission yields has been performed at the upgraded IGISOL-4 facility at the University of Jyväskylä, Finland. The fission products from high-energy neutron-induced fission of nat U were stopped in a gas cell filled with helium buffer gas, and were online separated with a dipole magnet. The isobars, with masses in the range A = 128-133 , were transported to a tape-implantation station and identified using γ -spectroscopy. We report here the relative cumulative isotopic yields of tin (Z = 50) and the relative independent isotopic yields of antimony (Z = 51). Isomeric yield ratios were also obtained for five nuclides. The yields of tin show a …

Masses of neutron-rich Ni and Cu isotopes and the shell closure at Z = 28 , N = 40

The Penning trap mass spectrometer JYFLTRAP, coupled to the Ion Guide Isotope Separator On-Line (IGISOL) facility at Jyvaskyla, was employed to measure the atomic masses of neutron-rich 70-73Ni and 73, 75Cu isotopes with a typical accuracy less than 5keV. The mass of 73Ni was measured for the first time. Comparisons with the previous data are discussed. Two-neutron separation energies show a weak subshell closure at 68 28Ni40 . A well established proton shell gap is observed at Z = 28 .

Evidence of a sudden increase in the nuclear size of proton-rich silver-96

Understanding the evolution of the nuclear charge radius is one of the long-standing challenges for nuclear theory. Recently, density functional theory calculations utilizing Fayans functionals have successfully reproduced the charge radii of a variety of exotic isotopes. However, difficulties in the isotope production have hindered testing these models in the immediate region of the nuclear chart below the heaviest self-conjugate doubly-magic nucleus 100Sn, where the near-equal number of protons (Z) and neutrons (N) lead to enhanced neutron-proton pairing. Here, we present an optical excursion into this region by crossing the N = 50 magic neutron number in the silver isotopic chain with th…

Nuclear moments and charge radii of the171Hf ground state and isomer

The magnetic moment, quadrupole moment and mean-square charge radial changes, relative to 172Hf, have been measured for the 171Hf ground state and the ½-[521] isomeric state, using on-line laser spectroscopy. The magnetic moments of the isomer and ground states are found to be + 0.526(16)µn and -0.674(12)µn, respectively. The spectroscopic quadrupole moment of the ground state is found to be +3.463(27) b. No change in mean-square charge radius is observed between the ground state and isomeric state. The observation of an inversion in the odd-even staggering at 171Hf is consistent with the suggested deformation trends.

COLLINEAR LASER SPECTROSCOPY ON NEUTRON-RICH Mn ISOTOPES APPROACHING N = 40

We have studied 51,53−64Mn (Z=25) via bunched-beam collinear laser spectroscopy at ISOLDE, CERN. Model-independent information on the ground- and isomeric state spins, as well as their g-factors is obtained from the measured hyperfine spectra. The spins are essential for further establishing the level schemes in the mass region, while the g-factors reveal the changing ground state wave functions in the Mn chain approaching N=40. ispartof: pages:699-702 ispartof: Acta Physica Polonica B vol:46 issue:3 pages:699-702 ispartof: location:Zakopane, Poland status: published

Characterization and performance of the DTAS detector

11 pags., 16 figs., 3 tabs.

The MORA project

The MORA (Matter's Origin from the RadioActivity of trapped and oriented ions) project aims at measuring with unprecedented precision the D correlation in the nuclear beta decay of trapped and oriented ions. The D correlation offers the possibility to search for new CP-violating interactions, complementary to searches done at the LHC and with Electric Dipole Moments. Technically, MORA uses an innovative in-trap orientation method which combines the high trapping efficiency of a transparent Paul trap with laser orientation techniques. The trapping, detection, and laser setups are under development, for first tests at the Accelerator laboratory, JYFL, in the coming years.

The FURIOS laser ion source at IGISOL-4

Abstract The FURIOS laser ion source at the Accelerator Laboratory of the University of Jyvaskyla has been moved to a new location as a part of the IGISOL-4 facility. The laser ion source project had a high priority which allowed the transport of laser light to be optimized during the design phase. The laser resonators have been upgraded with a dual etalon configuration leading to greatly reduced laser linewidth. The transport efficiency of the dual-chamber gas cell has been determined using an alpha recoil source, with efficiencies ranging from a few percent in the beam interaction chamber to nearly 20% in the ionization chamber. In addition, we present recent results from the re-commissio…

Beta Decay Studies of Neutron Rich Nuclei Using Total Absorption Gamma-ray Spectroscopy and Delayed Neutron Measurements

International audience; A complete characterisation of the β-decay of neutron-rich nuclei can be obtained from the measurement of β-delayed gamma rays and, whenever the process is energetically possible, β-delayed neutrons. The accurate determination of the β-intensity distribution and the β-delayed neutron emission probability is of great relevance in the fields of reactor technology and nuclear astrophysics. A programme for combined measurements using the total absorption gamma-ray spectroscopy technique and both neutron counters and neutron time-of-flight spectrometers is presented.

Precision 71Ga – 71Ge mass-difference measurement

The 71Ga(νe, e−) 71Ge reaction Q value has been measured with the JYFLTRAP mass spectrometer at the IGISOL facility of the University of Jyv¨askyl¨a to Q = 232.443(93) keV. This value agrees with previous measurements, though it features a much higher accuracy. The Q value is being discussed in the context of the solar neutrino capture rate in 71Ga. peerReviewed

The MARA-LEB ion transport system

A low-energy branch is under development for the MARA vacuum-mode recoil separator at the Accelerator Laboratory of the University of Jyväskylä. This development will allow for the study of proton-rich nuclei through laser ionisation spectroscopy and mass measurements. After stopping and extraction from a buffer gas cell, the ions of interest will be accelerated and transported to dedicated experimental setups by an ion transport system consisting of several focusing, accelerating and mass-separating elements. This article presents the current design and simulations for the ion transport. peerReviewed

Branching ratios in theβdecays ofN12andB12

Absolute branching ratios to unbound states in C-12 populated in the beta decays of N-12 and B-12 are reported. Clean sources of N-12 and B-12 were obtained using the isotope separation on-line (ISOL) method. The relative branching ratios to the different populated states were extracted using single-alpha as well as complete kinematics triple-alpha spectra. These two largely independent methods give consistent results. Absolute normalization is achieved via the precisely known absolute branching ratio to the bound 4.44 MeV state in C-12. The extracted branching ratios to the unbound states are a factor of three more precise than previous measurements. Branching ratios in the decay of Na-20 …

Cooling and bunching of ion beams for collinear laser spectroscopy

A greatly increased sensitivity in collinear laser spectroscopy experiments has been achieved by the application of new on-line ion cooling and bunching techniques. Cooling of a low-energy ion beam to low emittance and low velocity spread is shown to increase the peak efficiency while bunching the beam results in highly efficient background suppression.

Breakup channels forC12triple-αcontinuum states

The triple-alpha-particle breakup of states in the triple-alpha continuum of C-12 has been investigated by way of coincident detection of all three alpha particles of the breakup. The states have been fed in the beta decay of N-12 and B-12, and the alpha particles measured using a setup that covers all of the triple-alpha phase space. Contributions from the breakup through the Be-8(0(+)) ground state as well as other channels-interpreted as breakup through excited energies in Be-8-have been identified. Spins and parities of C-12 triple-alpha continuum states are deduced from the measured phase-space distributions for breakup through Be-8 above the ground state by comparison to a fully symme…

Enhancedγ-Ray Emission from Neutron Unbound States Populated inβDecay

Total absorption spectroscopy is used to investigate the β-decay intensity to states above the neutron separation energy followed by γ-ray emission in (87,88)Br and (94)Rb. Accurate results are obtained thanks to a careful control of systematic errors. An unexpectedly large γ intensity is observed in all three cases extending well beyond the excitation energy region where neutron penetration is hindered by low neutron energy. The γ branching as a function of excitation energy is compared to Hauser-Feshbach model calculations. For (87)Br and (88)Br the γ branching reaches 57% and 20%, respectively, and could be explained as a nuclear structure effect. Some of the states populated in the daug…

A neutron source for IGISOL-JYFLTRAP : Design and characterisation

A white neutron source based on the Be(p, nx) reaction for fission studies at the IGISOL-JYFLTRAP facility has been designed and tested. 30MeV protons impinge on a 5mm thick water-cooled beryllium disc. The source was designed to produce at least 1012 fast neutrons/s on a secondary fission target, in order to reach competitive production rates of fission products far from the valley of stability. The Monte Carlo codes MCNPX and FLUKA were used in the design phase to simulate the neutron energy spectra. Two experiments to characterise the neutron field were performed: the first was carried out at The Svedberg Laboratory in Uppsala (SE), using an Extended-Range Bonner Sphere Spectrometer and …

First Precision Mass Measurements of Refractory Fission Fragments

Atomic masses of 95-100Sr, 98-105Zr, and [corrected] 102-110Mo and have been measured with a precision of 10 keV employing a Penning trap setup at the IGISOL facility. Masses of 104,105Zr and 109,110Mo are measured for the first time. Our improved results indicate significant deviations from the previously published values deduced from beta end point measurements. The most neutron-rich studied isotopes are found to be significantly less bound (1 MeV) compared to the 2003 atomic mass evaluation. A strong correlation between nuclear deformation and the binding energy is observed in the two-neutron separation energy in all studied isotope chains.

Recent Advances in On-Line Laser Spectroscopy

At radioactive ion beam facilities, particle accelerators are employed to induce nuclear reactions in order to provide short-lived nuclei for immediate study using a variety of spectroscopic techniques. These exotic isotopes/isomers are formed into a beam of fast ions, which are mass analyzed in-flight during transport to a chosen experimental set-up. As an additional filter, the atomic level structure provides a selective fingerprint, which distinguishes one element from another due to the varying numbers of protons and electrons. This property is exploited in laser ion sources whereby high power, pulsed tuneable laser radiation is used to excite and ionize the atom in order to enhance the…

Phase-Imaging Ion-Cyclotron-Resonance technique at the JYFLTRAP double Penning trap mass spectrometer

The Phase-Imaging Ion-Cyclotron-Resonance (PI-ICR) technique has been commissioned at the JYFLTRAP double Penning trap mass spectrometer. This technique is based on projecting the ion motion in the Penning trap onto a position-sensitive multichannel-plate ion detector. Mass measurements of stable 85 Rb $ ^{+}$ and 87 Rb $ ^{+}$ ions with well-known mass values show that relative uncertainties $ \Delta m/m \leq 7\cdot 10^{-10}$ are possible to reach with the PI-ICR technique at JYFLTRAP. The significant improvement both in resolving power and in precision compared to the conventional Time-of-Flight Ion Cyclotron Resonance technique will enable measurements of close-lying isomeric states and …

QECvalues of the superallowedβemittersC10,Ar34,Ca38, andV46

The ${Q}_{\mathrm{EC}}$ values of the superallowed ${\ensuremath{\beta}}^{+}$ emitters $^{10}\mathrm{C}$, $^{34}\mathrm{Ar}$, $^{38}\mathrm{Ca}$, and $^{46}\mathrm{V}$ have been measured with the JYFLTRAP Penning-trap mass spectrometer to be 3648.12(8), 6061.83(8), 6612.12(7), and 7052.44(10) keV, respectively. All four values are substantially improved in precision over previous results. Of the well-known superallowed emitters, only $^{14}\mathrm{O}$ has yet to have had its ${Q}_{\mathrm{EC}}$ value measured with a Penning trap.

Gas jet studies towards an optimization of the IGISOL LIST method

Abstract Gas jets emitted from an ion guide have been studied as a function of nozzle type and gas cell-to-background pressure ratio in order to obtain a low divergent, uniform jet over a distance of several cm. The jet has been probed by imaging the light emitted from excited argon or helium gas atoms. For a simple exit hole or converging-diverging nozzle, the jet diameter was found to be insensitive to the nozzle shape and inlet pressure. Sonic jets with a FWHM below 6 mm were achieved with a background pressure larger than 1 mbar in the expansion chamber. The measurements are supported by the detection of radioactive 219 Rn recoils from an alpha recoil source mounted within the gas cell.…

First experiment with the NUSTAR/FAIR Decay Total Absorption γ-Ray Spectrometer (DTAS) at the IGISOL IV facility

V. Guadilla et al. ; 4 págs.; 4 figs.; 1 tab.

Nuclear mean-square charge radii of $^{63,64,66,68−82}$Ga nuclei: No anomalous behavior at N=32

Collinear laser spectroscopy was performed on the 63,64,66,68−82Ga isotopes with neutron numbers from N = 32 to N = 51. These measurements were carried out at the ISOLDE radioactive ion beam facility at CERN. Here we present the nuclear mean-square charge radii extracted from the isotope shifts and, for the lighter isotopes, new spin and moment values. New ground-state nuclear spin and moments were extracted from the hyperfine spectra of 63,70Ga, measured on an atomic transition in the neutral atom. The ground-state spin of 63Ga is determined to be I = 3/2. Analysis of the trend in the change in mean-square charge radii of the gallium isotopes demonstrates that there is no evidence of anoma…

Mass measurements of neutron-deficient nuclides close to A=80 with a Penning trap

The masses of 80,81,82,83Y, 83,84,85,86,88Zr and 85,86,87,88Nb have been measured with a typical precision of 7 keV by using the Penning trap setup at IGISOL. The mass of 84Zr has been measured for the first time. These precise mass measurements have improved Sp and QEC values for astrophysically important nuclides. peerReviewed

JYFLTRAP: a Penning trap for precision mass spectroscopy and isobaric purification

In this article a comprehensive description and performance of the double Penning-trap setup JYFLTRAP will be detailed. The setup is designed for atomic mass measurements of both radioactive and stable ions and additionally serves as a very high-resolution mass separator. The setup is coupled to the IGISOL facility at the accelerator laboratory of the University of Jyväskylä. The trap has been online since 2003 and it was shut down in the summer of 2010 for relocation to the upgraded IGISOL facility. Numerous atomic mass and decay energy measurements have been performed using the time-of-flight ion-cyclotron resonance technique. The trap has also been used in several decay spectroscopy expe…

Efficient, high-resolution resonance laser ionization spectroscopy using weak transitions to long-lived excited states

Laser spectroscopic studies on minute samples of exotic radioactive nuclei require very efficient experimental techniques. In addition, high resolving powers are required to allow extraction of nuclear structure information. Here we demonstrate that by using weak atomic transitions, resonance laser ionization spectroscopy is achieved with the required high efficiency (1%–10%) and precision (linewidths of tens of MHz). We illustrate experimentally and through the use of simulations how the narrow experimental linewidths are achieved and how distorted resonance ionization spectroscopy line shapes can be avoided. The role of the delay of the ionization laser pulse with respect to the excitatio…

Development of a carbon-cluster ion source for JYFLTRAP

Abstract A carbon-cluster ion source based on laser ablation and ionization of a carbon sample has been built and tested for the JYFLTRAP setup. In the present configuration the ion source is situated in the electrostatic switchyard in front of the radiofrequency (RFQ) cooler and buncher. In this position the beam quality of the carbon clusters injected into the Penning trap system is considerably improved by the RFQ. Moreover, the mass-dependence of the RFQ’s transmission can be used to some extent to suppress unwanted cluster sizes.

Characterization of a cylindrical plastic {\beta}-detector with Monte Carlo simulations of optical photons

V. Guadilla et al. -- 5 pags., 8 figs., tab.

Direct measurement of the mass difference of As72−Ge72 rules out As72 as a promising β -decay candidate to determine the neutrino mass

We report the first direct determination of the ground-state to ground-state electron-capture $Q$ value for the $^{72}\mathrm{As}$ to $^{72}\mathrm{Ge}$ decay by measuring their atomic mass difference utilizing the double Penning trap mass spectrometer, JYFLTRAP. The $Q$ value was measured to be 4343.596(75) keV, which is more than a fiftyfold improvement in precision compared to the value in the most recent Atomic Mass Evaluation 2020. Furthermore, the new $Q$ value was found to be 12.4(40) keV (3.1 $\ensuremath{\sigma}$) lower. With the significant reduction of the uncertainty of the ground-state to ground-state $Q$ value combined with the level scheme of $^{72}\mathrm{Ge}$ from $\ensurem…

Fission yield measurements at IGISOL

The fission product yields are an important characteristic of the fission process. In fundamental physics, knowledge of the yield distributions is needed to better understand the fission process. For nuclear energy applications good knowledge of neutroninduced fission-product yields is important for the safe and efficient operation of nuclear power plants. With the Ion Guide Isotope Separator On-Line (IGISOL) technique, products of nuclear reactions are stopped in a buffer gas and then extracted and separated by mass. Thanks to the high resolving power of the JYFLTRAP Penning trap, at University of Jyväskylä, fission products can be isobarically separated, making it possible to measure rela…

High-resolution laser system for the S3-Low Energy Branch

International audience; In this paper we present the first high-resolution laser spectroscopy results obtained at the GISELE laser laboratory of the GANIL-SPIRAL2 facility, in preparation for the first experiments with the S$^3$-Low Energy Branch. Studies of neutron-deficient radioactive isotopes of erbium and tin represent the first physics cases to be studied at S$^3$. The measured isotope-shift and hyperfine structure data are presented for stable isotopes of these elements. The erbium isotopes were studied using the $4f^{12}6s^2$$^3H_6 \rightarrow 4f^{12}(^3 H)6s6p$$J = 5$ atomic transition (415 nm) and the tin isotopes were studied by the $5s^25p^2 (^3P_0) \rightarrow 5s^25p6s (^3P_1)$…

Trap-assisted separation of nuclear states for gamma-ray spectroscopy: the example of100Nb

Low-lying levels in 100Mo are known to be populated by beta decay from both the ground and isomeric states in 100Nb. The small energy difference (~3 ppm) between the two parent states and the similarity of their half-lives make it difficult to distinguish experimentally between the two decay paths. A new technique for separating different states of nuclei has recently been developed in a series of experiments at the IGISOL facility, using the JYFLTRAP installation, at the University of Jyvaskyla where mass resolution ~2 ppm was achieved in mass measurements and in the production of 133mXe. This paper reports on the extension of this technique to allow the separate study of the gamma-ray dec…

Isomeric fission yield ratios for odd-mass Cd and In isotopes using the Phase-Imaging Ion-Cyclotron-Resonance technique

Isomeric yield ratios for the odd-$A$ isotopes of $^{119-127}$Cd and $^{119-127}$In from 25-MeV proton-induced fission on natural uranium have been measured at the JYFLTRAP double Penning trap, by employing the Phase-Imaging Ion-Cyclotron-Resonance technique. With the significantly improved mass resolution of this novel method isomeric states separated by 140 keV from the ground state, and with half-lives of the order of 500 ms, could be resolved. This opens the door for obtaining new information on low-lying isomers, of importance for nuclear structure, fission and astrophysics. In the present work the experimental isomeric yield ratios are used for the estimation of the root-mean-square a…

An inductively heated hot cavity catcher laser ion source.

An inductively heated hot cavity catcher has been constructed for the production of low-energy ion beams of exotic, neutron-deficient Ag isotopes. A proof-of-principle experiment has been realized by implanting primary (107)Ag(21+) ions from a heavy-ion cyclotron into a graphite catcher. A variable-thickness nickel foil was used to degrade the energy of the primary beam in order to mimic the implantation depth expected from the heavy-ion fusion-evaporation recoils of N = Z (94)Ag. Following implantation, the silver atoms diffused out of the graphite and effused into the catcher cavity and transfer tube, where they were resonantly laser ionized using a three-step excitation and ionization sc…

Intracavity Frequency Doubling and Difference Frequency Mixing for Pulsed ns Ti:Sapphire Laser Systems at On-Line Radioactive Ion Beam Facilities

Intra-cavity second harmonic generation of a Titanium:sapphire (Ti:sa) laser system has been used to improve the conversion efficiency to the second harmonic. Over the course of several experiments performance data spanning the whole wavelength range of a Ti:sa has been collected, which may be used as a guideline for future experiments. An average output power of up to 3.7 W was achieved, resulting in a conversion efficiency of >75 % to the second harmonic. A wavelength coverage from 340-525 nm has been demonstrated. To extend the wavelength range of the solid state laser system, difference frequency mixing has been applied to the intra-cavity doubled light and the fundamental output of a s…

Ultra-high resolution mass separator—Application to detection of nuclear weapons tests

Abstract A Penning trap-based purification process having a resolution of about 1 ppm is reported. In this context, we present for the first time a production method for the most complicated and crucially important nuclear weapons test signature, 133mXe. These pure xenon samples are required by the Comprehensive Nuclear-Test-Ban Treaty Organization to standardize and calibrate the worldwide network of xenon detectors.

An ion guide for the production of a low energy ion beam of daughter products of α-emitters

A new ion guide has been modeled and tested for the production of a low energy ($\approx$ 40 kV) ion beam of daughter products of alpha-emitting isotopes. The guide is designed to evacuate daughter recoils originating from the $\alpha$-decay of a $^{233}$U source. The source is electroplated onto stainless steel strips and mounted along the inner walls of an ion guide chamber. A combination of electric fields and helium gas flow transport the ions through an exit hole for injection into a mass separator. Ion guide efficiencies for the extraction of $^{229}$Th$^{+}$ (0.06%), $^{221}$Fr$^{+}$ (6%), and $^{217}$At$^{+}$ (6%) beams have been measured. A detailed study of the electric field and …

Large Impact of the Decay of Niobium Isomers on the Reactor ν¯e Summation Calculations

Even mass neutron-rich niobium isotopes are among the principal contributors to the reactor antineutrino energy spectrum. They are also among the most challenging to measure due to the refractory nature of niobium, and because they exhibit isomeric states lying very close in energy. The beta-intensity distributions of Nb-100gs,Nb-100m and Nb-102gs,Nb-02m beta decays have been determined using the total absorption.-ray spectroscopy technique. The measurements were performed at the upgraded Ion Guide Isotope Separator On-Line facility at the University of Jyvaskyla. Here, the double Penning trap system JYFLTRAP was employed to disentangle the beta decay of the isomeric states. The new data ob…

Status and development of the MARA low-energy branch

The MARA Low-Energy Branch is under development at the Accelerator Laboratory of the University of Jyvaskylä. The facility will be employed for laser ionisation and spectroscopy studies and for mass measurements of nuclei close to the proton drip line. This article presents an updated status of the ongoing development of the different parts of this facility, including the buffer gas cell, the ion transport system, the laser system and the detector stations. peerReviewed

Study of the radiative decay of the low-energy isomer in ${}^{229}$Th

Measurement of the 2+→0+ ground-state transition in the β decay of F20

We report the first detection of the second-forbidden, nonunique, 2+→0+, ground-state transition in the β decay of F20. A low-energy, mass-separated F+20 beam produced at the IGISOL facility in Jyvaskyla, Finland, was implanted in a thin carbon foil and the β spectrum measured using a magnetic transporter and a plastic-scintillator detector. The β-decay branching ratio inferred from the measurement is bβ=[0.41±0.08(stat)±0.07(sys)]×10-5 corresponding to logft=10.89(11), making this one of the strongest second-forbidden, nonunique β transitions ever measured. The experimental result is supported by shell-model calculations and has significant implications for the final evolution of stars tha…

Total absorption study of theβdecay of102,104,105Tc

The $\ensuremath{\beta}$-feeding probabilities for three important contributors to the decay heat in nuclear reactors, namely ${}^{102,104,105}$Tc, have been measured using the total absorption spectroscopy technique. For the measurements, sources of very high isobaric purity have been obtained using a Penning trap (JYFLTRAP). A detailed description of the data analysis is given and the results are compared with high-resolution measurements and theoretical calculations.

TAGS measurements of $^{100}$Nb ground and isomeric states and $^{140}$Cs for neutrino physics with the new DTAS detector

V. Guadilla et al. -- 4 pags., 6 figs. -- Open Access funded by Creative Commons Atribution Licence 4.0

Laser spectroscopy for nuclear structure physics

High-resolution laser spectroscopy is an established powerful tool in the study of nuclear shape, size and multipole moments. Measurements of the hyperfine structures and isotope shifts in the atomic spectra of radioactive nuclei provide unique insight into the evolution of the nuclear macroscopic shape and microscopic structure. These measurements can be made with high precision and high sensitivity and applied directly on-line at radioactive nuclear beam facilities. Recent measurements, advances at facilities and the future direction of the field are reviewed. A summary of experimental data is presented. peerReviewed

QEC value of the superallowed β emitter 42Sc

The QEC value of the superallowed β+ emitter Sc42 has been measured with the JYFLTRAP Penning-trap mass spectrometer at the University of Jyväskylä to be 6426.350(53) keV. This result is at least a factor of four more precise than all previous measurements, which were also inconsistent with one another. As a byproduct we determine the excitation energy of the 7+ isomeric state in Sc42 to be 616.762(46) keV, which deviates by 8σ from the previous measurement. peerReviewed

Laser spectroscopy of gallium isotopes beyond N = 50

The installation of an ion-beam cooler-buncher at the ISOLDE, CERN facility has provided increased sensitivity for collinear laser spectroscopy experiments. A migration of single-particle states in gallium and in copper isotopes has been investigated through extensive measurements of ground state and isomeric state hyperfine structures. Lying beyond the N = 50 shell closure, 82Ga is the most exotic nucleus in the region to have been studied by optical methods, and is reported here for the first time. ispartof: pages:012071-6 ispartof: Journal of Physics: Conference Series vol:381 issue:1 pages:012071-6 ispartof: Rutherford Centennial Conference on Nuclear Physics location:Manchester, UK dat…

New isomer and decay half-life ofRu115

Exotic, neutron-rich nuclei of mass $A=115$ produced in proton-induced fission of $^{238}\mathrm{U}$ were extracted using the IGISOL mass separator. The beam of isobars was transferred to the JYFLTRAP Penning trap system for further separation to the isotopic level. Monoisotopic samples of $^{115}\mathrm{Ru}$ nuclei were used for $\ensuremath{\gamma}$and $\ensuremath{\beta}$ coincidence spectroscopy. In $^{115}\mathrm{Ru}$ we have observed excited levels, including an isomer with a half-life of 76(6) ms and ($7/{2}^{\ensuremath{-}}$) spin and parity. The first excited 61.7-keV level in $^{115}\mathrm{Ru}$ with spins and parity ($3/{2}^{+}$) may correspond to an $\mathit{oblate}$ $3/{2}^{+}$…

QEC value of the superallowed β emitter Sc42

Precise measurements of superallowed ${0}^{+}\ensuremath{\rightarrow}{0}^{+}$ $\ensuremath{\beta}$ decay presently provide the most precise value for the weak mixing amplitude ${V}_{u\phantom{\rule{0}{0ex}}d}$. As the largest element of the CKM matrix, ${V}_{u\phantom{\rule{0}{0ex}}d}$ is a critical piece of the Standard Model of the electroweak interaction. The new, precise Penning-trap mass measurement of the decay energy for the superallowed transition in ${}^{42}$Sc opens the door for a much more precise $f\phantom{\rule{0}{0ex}}t$ value determination if its half-life can be measured more precisely as well.

Alternative approach to populate and study the $^{229}Th$ nuclear clock isomer

A new approach to observe the radiative decay of the $^{229}$Th nuclear isomer, and to determine its energy and radiative lifetime, is presented. Situated at a uniquely low excitation energy, this nuclear state might be a key ingredient for the development of a nuclear clock, a nuclear laser and the search for time variations of the fundamental constants. The isomer's $\gamma$ decay towards the ground state will be studied with a high-resolution VUV spectrometer after its production by the $\beta$ decay of $^{229}$Ac. The novel production method presents a number of advantages asserting its competitive nature with respect to the commonly used $^{233}$U $\alpha$-decay recoil source. In this …

Total absorption spectroscopy study of the β decay of Br86 and Rb91

The beta decays of 86Br and 91Rb have been studied using the total absorption spectroscopy technique. The radioactive nuclei were produced at the IGISOL facility in Jyvaskyla and further purified using the JYFLTRAP. 86Br and 91Rb are considered high priority contributors to the decay heat in reactors. In addition 91Rb was used as a normalization point in direct measurements of mean gamma energies released in the beta decay of fission products by Rudstam et al. assuming that this decay was well known from high-resolution measurements. Our results shows that both decays were suffering from the Pandemonium effect and that the results of Rudstam et al. should be renormalized.

Quenching of the SnSbTe Cycle in therpProcess

The nuclides 104-108Sn, 106-110Sb, 108,109Te, and 111I at the expected endpoint of the astrophysical rp process have been produced in 58Ni+natNi fusion-evaporation reactions at IGISOL and their mass values were precisely measured with the JYFLTRAP Penning trap mass spectrometer. For 106Sb, 108Sb, and 110Sb these are the first direct experimental mass results obtained. The related one-proton separation energies have been derived and the value for 106Sb, Sp=424(8) keV, shows that the branching into the closed SnSbTe cycle in the astrophysical rp process is weaker than expected.

Collinear laser spectroscopy of ZrII

A new technique involving collinear laser spectroscopy of ion bunches has been used to study the radio-isotopes 87,87m,88,89,89m Zr.

Nuclear moments and charge radii of bismuth isotopes

Isotope shifts and hyperfine structures have been measured on the 306.7 nm line in bismuth isotopes with A = 205-210, 210m, 212 and 213 by gas cell laser spectroscopy. More precise measurements were made for the A = 207-209 isotopes in atomic beam measurements. Nuclear magnetic and quadrupole moments were deduced. A detailed comparison of the nuclear charge radii systematics has been made in the region using a King plot technique.

Disentangling decaying isomers and searching for signatures of collective excitations in β decay

6 pags., 3 figs., 1 tab. -- 27th International Nuclear Physics Conference (INPC2019) 29 July - 2 August 2019, Glasgow, UK

High-resolution, accurate multiple-reflection time-of-flight mass spectrometry for short-lived, exotic nuclei of a few events in their ground and low-lying isomeric states

Physical review / C covering nuclear physics 99(6), 064313 (2019). doi:10.1103/PhysRevC.99.064313