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

High-precision mass measurement ofS31with the double Penning trap JYFLTRAP improves the mass value forCl32

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

Experimental studies at JYFLTRAP

JYFLTRAP is a Penning trap system at the accelerator laboratory in Jyvaskyla, Finland that enables high-precision experiments with stored, exotic species that are produced at the IGISOL facility. On one hand, these can be performed within the trap itself, like e.g. mass spectrometry. On the other hand, the trap can be used to provide the highly purified species for further experiments, e.g. for trap-assisted nuclear decay spectroscopy. This contribution focuses on these two possible applications with the presentation of some recent results on superallowed beta decays.

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 ${…

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].

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.

On the resonant neutrinoless double-electron-capture decay of ^{136}Ce

Abstract The double-electron-capture Q value for the 136Ce decay to 136Ba has been determined at JYFLTRAP. The measured value 2378.53(27) keV excludes the energy degeneracy with the 0 + excited state of the decay daughter 136Ba at 2315.32(7) keV in a resonant 0 ν ECEC decay by 11.67 keV. The new Q value differs from the old adopted value 2419(13) keV (Atomic Mass Evaluation 2003) by 40 keV and is 50 times more precise. Our calculations show that the precise Q value renders the resonant 0 ν ECEC decay of 136Ce undetectable by the future underground detectors. We measured also the double-β decay Q value of 136Xe to be 2457.86(48) keV which agrees well with the value 2457.83(37) keV measured a…

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 …

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…

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…

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

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…

Conversion electron spectroscopy at IGISOL

Conversion elecron spectroscopy has been an important part of the nuclear spectrocopy research at the Department of Physics of the University of Jyv¨askyl¨a since the commissioning of the first cyclotron in the mid 1970s. At the IGISOL facility a specialiced conversion electron spectrometer ELLI was developed in the late 1980s. The first results with ELLI were obtained using the beams from the old MC-20 cyclotron to study newly discovered isotopes of refractory fission products. In the present K130 cyclotron laboratory ELLI has been utilized in many decay-spectroscopy experiments both neutron-deficient and neutron-rich side of the valley of stability. In the early 2000s the new JYFLTRAP ion…

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…

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.

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.

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…

Penning-trap-assisted decay spectroscopy studies of neutron-rich nuclei in the A = 110 region

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…

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…

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 …

Isomer and decay studies for the rp process at IGISOL

This article reviews the decay studies of neutron-deficient nuclei within the mass region \ensuremathA=56--100 performed at the Ion-Guide Isotope Separator On-Line (IGISOL) facility in the University of Jyväskylä over last 25 years. Development from He-jet measurements to on-line mass spectrometry, and eventually to atomic mass measurements and post-trap spectroscopy at IGISOL, has yielded studies of around 100 neutron-deficient nuclei over the years. The studies form a solid foundation to astrophysical rp -process path modelling. The focus is on isomers studied either via spectroscopy or via Penning-trap mass measurements. The review is complemented with recent results on the ground and is…

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.

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…

Precise half-life measurement of the Si-26 ground state

The beta-decay half-life of 26Si was measured with a relative precision of 1.4*10e3. The measurement yields a value of 2.2283(27) s which is in good agreement with previous measurements but has a precision that is better by a factor of 4. In the same experiment, we have also measured the non-analogue branching ratios and could determine the super-allowed one with a precision similar to the previously reported measurements. The experiment was done at the Accelerator Laboratory of the University of Jyvaskyla where we used the IGISOL technique with the JYFLTRAP facility to separate pure samples of 26Si.

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…

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…

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…

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

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…

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…

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…

Trap-assisted studies of odd, neutron-rich isotopes from Tc to Pd

We review the present and future of trap-assisted structure studies of odd, neutron-rich Tc, Ru, Rh and Pd isotopes at the limits of present experimental techniques. These nuclei of refractory elements are produced in light-particle induced fission and filtered by their mass number with the IGISOL mass separator. Further mass separation with the JYFLTRAP Penning trap system provides a clean, monoisotopic beam perfectly suited for precise nuclear spectroscopy. Connecting the IGISOL and the JYFLTRAP facilities to the recently installed MCC30/15 cyclotron opens new prospects for post-trap spectroscopy of very exotic, neutron-rich nuclei. peerReviewed

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…

Study of Proton and 3He Induced Reactions on 235U at Low Energies

Abstract Highly enriched 235 U targets were irradiated with 6.5 − 16.1 MeV protons and 20.4 − 42.0 MeV 3 He ions. The irradiated targets were measured with γ and α spectrometric methods to identify and quantify the produced reaction products. After primary activity measurements the targets were dissolved, and interesting Pu and Np reaction products were chemically separated from the target material, and measured for activity again. From the activity results it was possible to calculate the reaction cross sections for differently produced nuclides. The data obtained from the experiment resulted in earlier unknown excitation functions on proton and 3 He induced nuclear reactions on 235 U.

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

Low-spin structure of85Se and theβnbranching of85As

Fission fragments from neutron-induced fission of ${}^{235}$U produced at the high-flux reactor of the Institut Laue-Langevin, Grenoble, were separated with the Lohengrin separator to provide a beam of neutron-rich ${}^{85}\phantom{\rule{-0.16em}{0ex}}$As nuclei. The ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay of ${}^{85}\phantom{\rule{-0.16em}{0ex}}$As to ${}^{85}$Se was studied using $\ensuremath{\gamma}$-$\ensuremath{\gamma}$ and $\ensuremath{\beta}$-$\ensuremath{\gamma}$ coincidence techniques. ${}^{85}$Se was also studied using the prompt-$\ensuremath{\gamma}$ coincidence data from spontaneous fission of ${}^{248}$Cm and ${}^{252}$Cf measured with the Eurogam2 and Gammasphere Ge arra…

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.

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…

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…

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…

Quenching of the SnSbTe Cycle in the rp-Process

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…

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…

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.

Recent mass measurements for the r process at JYFLTRAP

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…

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 .

Coulomb displacement energies as a probe for nucleon pairing in the $f_{7/2}$ shell

Coulomb displacement energies of $T=1/2$ mirror nuclei have been studied via a series of high-precision $Q_\mathrm{EC}$-value measurements with the double Penning trap mass spectrometer JYFLTRAP. Most recently, the $Q_\mathrm{EC}$ values of the $f_{7/2}$-shell mirror nuclei $^{45}$V ($Q_\mathrm{EC}=7123.82(22)$ keV) and $^{49}$Mn ($Q_\mathrm{EC}=7712.42(24)$ keV) have been measured with an unprecedented precision. The data reveal a 16-keV ($1.6\sigma$) offset in the adopted Atomic Mass Evaluation 2012 value of $^{49}$Mn suggesting the need for further measurements to verify the breakdown of the quadratic form of the isobaric multiplet mass equation. Precisely measured $Q_\mathrm{EC}$ values…

Preparing isomerically pure beams of short-lived nuclei at JYFLTRAP

A new procedure to prepare isomerically clean samples of ions with a mass resolving power of more than 100,000 has been developed at the JYFLTRAP tandem Penning trap system. The method utilises a dipolar rf-excitation of the ion motion with separated oscillatory fields in the precision trap. During a subsequent retransfer to the purification trap, the contaminants are rejected and as a consequence, the remaining bunch is isomerically cleaned. This newly-developed method is suitable for very high-resolution cleaning and is at least a factor of five faster than the methods used so far in Penning trap mass spectrometry.

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…

Double-beta decay Q values of 116Cd and 130Te

Abstract The Q values of the 116Cd and 130Te double-beta decaying nuclei were determined by using a Penning trap mass spectrometer. The new atomic mass difference between 116Cd and 116Sn of 2813.50(13) keV differs by 4.5 keV and is 30 times more precise than the previous value of 2809(4) keV. The new value for 130Te, 2526.97(23) keV is close to the Canadian Penning trap value of 2527.01 ± 0.32 keV (Scielzo et al., 2009) [1] , but differs from the Florida State University trap value of 2527.518 ± 0.013 keV (Redshaw et al., 2009) [2] by 0.55 keV (2σ). These values are sufficiently precise for ongoing neutrinoless double-beta decay searches in 116Cd and 130Te. Hence, our Q values were used to …

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.

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…

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…

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.

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.

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 $\mathit{oblate}$ $3/{2}^{+}$…

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.

AccurateQValue for theSn112Double-βDecay and its Implication for the Search of the Neutrino Mass

The $Q$ value of the $^{112}\mathrm{Sn}$ double-beta decay was determined by using a Penning trap mass spectrometer. The new atomic-mass difference between $^{112}\mathrm{Sn}$ and $^{112}\mathrm{Cd}$ of 1919.82(16) keV is 25 times more precise than the previous value of 1919(4) keV. This result removes the possibility of enhanced resonance capture of the neutrinoless double-EC decay to the excited ${0}^{+}$ state at 1871.00(19) keV in $^{112}\mathrm{Cd}$.

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.

High-precision mass measurement of 31S with the double Penning trap JYFLTRAP improves the mass value for 32Cl