0000000000822824
AUTHOR
A. Honkanen
Beta Decay of 111Tc to 111Ru
The β-decay of the very neutron-rich 111Tc nucleus has been observed. A partial decay scheme of 111Ru is presented, complementing the high-spin levels earlier reported in spontaneous fission work.
Proton dripline studies at ISOLDE: 31Ar and 9C
In this contribution examples of the application of new technologies to disentangle the mechanism of $\beta$-delayed multiparticle emission are given. In particular the mechanism of $\beta$2p-emission from $^{31}$Ar has been resolved and proved to be sequential, a preview of $^{9}$C-decay data is discussed.
First decay scheme of 113Tc and identification of 113Ru m
Very neutron–rich fission products of the mass chain A=113 obtained from the IGISOL on–line mass separator have been investigated by γγ coincidence techniques and γ-spectra multiscaling. Gamma–rays following β–decay of 113Tc have been observed for the first time and a new 0.5 s isomeric state has been found in 113Ru.
Status report of the Jyvaskyla ion guide isotope separator on-line facility
The ion guide isotope separator facility IGISOL of the University of Jyvaskyla has been moved to the new K-130 heavy ion cyclotron laboratory. The totally reconstructed facility is described in detail. The primary beams and targets, helium pumping, separator beam line construction and separator beam diagnostics are discussed. The spectroscopy stations are introduced with illustrative examples from the research program, including beta-delayed proton and neutron spectroscopy, gamma-ray spectroscopy with and without arrays, conversion electron spectroscopy, collinear laser spectroscopy and nuclear level lifetime spectroscopy.
Production of refractory elements close to the Z=N line using the ion-guide technique
Production of neutron-deficient isotopes of refractory elements in the A = 80-88 region was studied using the IGISOL technique and the 165 MeV Si-32 + Ni-nat reaction. Radioactive isotopes of Y through Mo could be produced up to the M-T = + 1 line. New information on the decay of the A = 82 and 85 nuclei, including a more detailed decay scheme and more accurate half-life for Y-82, was obtained. (C) 1998 Elsevier Science B.V. All rights reserved.
First observation of β decay ofNb108toMo108
The \ensuremath{\beta}-delayed \ensuremath{\gamma} decay of $^{108}\mathrm{Nb}$ has been studied using the on-line mass-separator technique. The measured \ensuremath{\beta}-decay half-life 0.20\ifmmode\pm\else\textpm\fi{}0.03 s agrees with the previous measurement based on \ensuremath{\beta}-delayed neutron detection. The lifetime of the first ${2}^{+}$ state in $^{108}\mathrm{Mo}$ was measured to be 0.5\ifmmode\pm\else\textpm\fi{}0.3 ns, which is consistent with a deformation \ensuremath{\beta}\ensuremath{\approxeq}0.4. Spin and parity of ${2}^{+}$ are suggested for the ground state of $^{108}\mathrm{Nb}$. \textcopyright{} 1996 The American Physical Society.
Spectroscopy at the drip line: the case of 31Ar
The beta decay of exotic nuclei is directly connected to many different and highly relevant issues. While along the years a hundred of nuclei have been identified as beta delayed proton (β-p) emitters only eight have been found to be β-2p emitters and the β-3p decay mode although energetically allowed has so far not been observed [1].
Gas-silicon detector telescope for charged particle spectroscopy
Abstract A gas-silicon detector telescope for charged particle spectroscopy has been constructed and tested. The lower detection limits were determined to be 155 keV for protons, 180 keV for deuterons and 350 keV for alpha particles. Typical energy resolution of the telescope measured for beta-delayed protons is 20 keV. Time resolution for the signals of the telescope was measured to be less than 10 ns. Examples of using the detector telescope in detection of beta-delayed proton activities are presented.
On-line laser spectroscopy of refractory radioisotopes at the JYFL IGISOL facility
A major objective of the laser-IGISOL program has been realized with the first ever on-line observation of collinear laser induced fluorescence from an ion of a refractory element. The measurements demonstrate that the IGISOL can be operated in a mode that produces ion beams of good emittance with reasonable extraction efficiency. The technique has been used to study the neutron-deficient Hf isotopes.
β-delayed neutron decay of 104Y, 112Tc, 113Tc and 114Tc: test of half-life predictions for neutron-rich isotopes of refractory elements
Abstract Beta-decay gross properties of neutron-rich isotopes 104Y and 112,113,114Tc produced in 25 MeV proton-induced fission of 238U have been measured. Decays of 104Y with a half-life of 180±60 ms and of 114Tc with a half-life of 150±30 ms are reported for the first time. Beta-delayed neutron emission probabilities of 112,113,114Tc are determined as (1.5±0.2)%, (2.1±0.3)% and (1.3±0.4)%, respectively. Comparison of the observed Pn values with a recent theoretical calculation based on deformed quasiparticle random phase approximation (QRPA) shows good overall agreement for Tc isotopes. However, comparison of beta-decay half-lives of neutron-rich isotopes of Y to Rh with the QRPA model and…
Neutron yields from thick 12C and 9Be targets irradiated by 50 and 65 MeV deuterons
Abstract Absolute intensities, angular distributions and energy spectra of neutrons emitted from thick 12 C and 9 Be targets irradiated with 50 and 65 MeV deuterons, respectively, have been measured. The neutron spectra were measured by time-of-flight (TOF) technique. The detectors provided continuous coverage from 0° to 60° where a significant angular dependence of emitted neutrons was found. The yield of 0.109(10) neutrons/deuteron from the 9 Be target is a factor of two higher than that from the 12 C target, 0.056(6) neutrons/deuteron. The hardness parameters of the neutron spectra are calculated for the radiation damage studies of the silicon devices.
Decay of the neutron-rich isotope 113Ru to 113Rh
The decay of neutron-rich isotope 113Ru obtained as on-line mass separated product of proton-induced fission has been investigated by γγ coincidence and spectrum multiscaling measurements. Decay schemes for both low- and high-spin isomers of 113Ru have been constructed. The level scheme of 113Rh is considerably extended. Systematics of the lowest-lying rhodium levels is smooth. The picture of shape coexistence established for neutron-rich Rh isotopes near-neutron midshell is confirmed with the observation of a K = 1/2 deformed band, with its 3/2+ state at 600 keV being the lowest-lying level and of probable 7/2+ and 5/2+ band members. A large fraction of β feeding is found to populate high-…
A new 400 ms isomer in125Ce→125La
By using the IGISOL technique, adapted for the study of products of heavy ion induced fusion-evaporation reactions, it has been possible to identify a new isomer in the mass chainA=125.
Two-proton emission in the decay of Ar-31
18 pages, 7 figures, 2 tables.-- PACS nrs.: 23.40.Hc; 27.30.+t.
Beta-Decay Half-Lives and Neutron-Emission Probabilities of Very Neutron-Rich Y to Tc Isotopes
Neutron-rich {sub 39}Y to {sub 43}Tc isotopes have been produced by fission of uranium with a 50MeV H{sub 2}{sup +} beam. Beta-decay half-lives, delayed neutron-emission probabilities, and production yields have been measured and compared with theory. Beta decay of 4 new isotopes is reported, and the {beta}-delayed neutron-emission mode has been discovered for 12 isotopes of the elements niobium and technetium. The results compared to quasiparticle random phase approximation predictions indicate the increasing importance of fast {beta} transitions to high-lying states of nuclei with large neutron excess. {copyright} {ital 1996 The American Physical Society.}
First collinear laser spectroscopy measurements of radioisotopes from an IGISOL ion source
Abstract The standard Doppler-free technique of collinear laser spectroscopy has been successfully applied to radioisotopes from the ion-guide isotope separator (IGISOL) at the University of Jyvaskyla. The laser resonance fluorescence signals for the 140,142,144 Ba radioisotopes show that the ion beam energy spread is less than 6 eV, allowing the laser technique to have both high resolution and a sensitivity comparable with the best obtained at conventional facilities.
Measurement of the IAS resonance strength in 23Mg
Abstract Beta decay of 23 Al to excited states in 23 Mg has been studied using low-energy proton and high-energy gamma-ray detection combined with ion-guide-based on-line mass separation. For the first time, a T =3/2 isobaric analogue state, at 7801(2) keV, was observed to decay by both proton and gamma emission, with a proton branching of 0.17(8)%. The deduced resonance strength ωγ =2.2(10) meV is in agreement with upper limits reported from 22 Na(p, γ ) reaction studies. Shell-model calculations are incorporated.
Level structure of 99Nb
The β decay of 97Sr to 97Y has been investigated using ion-guide on-line mass separation and a 10 Ge-detector array to record γ−γ coincidences to a detection limit well below that of former studies. Similarities are found in the β-decay patterns of 99Zr and of its isotone 97Sr and also in the γ-ray decay rates and branchings of the corresponding levels in their respective daughters 99Nb and 97Y. This indicates a persisting influence of the d5/2 neutron shell closure for 99Nb. The level structure of 99Nb and the β-feeding pattern are discussed in the frame of the interacting boson-fermion plus broken pair model and the microscopic quasiparticle phonon model.
Proton dripline studies at ISOLDE: 31Ar and 9C
In this contribution examples of the application of new technologies to disentangle the mechanism of beta-delayed multiparticle emission are given. In particular the mechanism of β-delayed two-proton emission from 31Ar has be resolved and proved to be sequential, a preview of 9C-decay data is discussed. peerReviewed
Fine structure in the beta-delayed proton decay of 33Ar
9 pages, 2 figures, 2 tables.-- PACS nrs.: 21.60.Cs; 23.40.−s; 27.30.+t; 29.30.Ep.
The β2p decay mechanism of Ar
We have measured the beta-decay of Ar-31 with a high granularity setup sensitive to multiparticle decay branches. Two-proton emission is observed from the isobaric analog state in Cl-31 to the four lowest states in P-29 and furthermore from a large number of states fed in Gamow-Teller transitions. The mechanism of two-proton emission is studied via energy and angular correlations between the two protons. In all cases the mechanism is found to be sequential yielding information about states in S-30 up to 8 MeV excitation energy. Improved data on the beta-delayed one-proton branches together with the two-proton data provide precise information about the beta-strength distribution up to 15 MeV…
Determination of the spin of 31Ar
Abstract The beta-delayed proton emission from the lightest Ar-isotopes has been recorded with a high-granularity, large solid-angle Si-detector set-up. Proton energy shifts due to beta-recoil have been measured. We demonstrate how this allows the spin of 31 Ar to be determined as 5/2. The method can be applied at decay rates as low as 1 s −1 .
New interpretation of shape coexistence in99Zr
Levels in ${}^{99}\mathrm{Zr}$ populated by $\ensuremath{\beta}$ decay of on-line mass separated ${}^{99}$Y have been studied by $\ensuremath{\gamma}$-ray spectroscopic methods, including $\ensuremath{\gamma}$-$\ensuremath{\gamma}$ coincidences recorded with an array of ten Ge detectors and level-lifetime measurements. The formerly reported strongly collective character of the 53-keV transition turns out to be questionable. This implies a revision of the experimental evidence for shape coexistence in ${}^{99}\mathrm{Zr}.$ Transition rates and $\ensuremath{\gamma}$-ray branching ratios make a new level at 679 keV with ${t}_{1/2}=9$ ns another candidate for a deformed state.
High-resolution studies of beta-delayed proton emitters at IGISOL facility
Beta-decays of23Al and41Ti have been studied by applying ion guide techniques, gamma detection and a gas-Si telescope for charged-particle detection. The experimental beta-decay strength of41Ti was found to be quenched by a factor ofq2 = 0.64 compared to our shell model calculations below 8 MeV excitation energy in41Sc. This result is in line with the generally accepted value ofq = 0.77. The isobaric analogue state of the41Ti ground state was measured to contain 10(8)% isospin impurity. This relatively high value could be well reproduced by the shell model calculation in thesdfp space. Gamma-decay of theT = 3/2 isobaric analogue state in23Mg was observed together with its decay by proton em…
Independent yields of neutron-rich nuclei in charged-particle induced fission
Abstract Yields of fission products have been studied at the recently upgraded IGISOL facility in Jyvaskyla using 50 MeV H2+ beam (Ep = 25 MeV) and thin natTh and natU targets. The independent yields of fission products in the mass regions A = 99−112 (elements Y, Nb and Tc) and A = 127−134 (elements Sn, Sb and Te) have been obtained. Comparisons of the experimental isotopic distributions with theoretical ones are presented. Enhancement of the production rate of the doubly magic 132Sn is observed in the experimental yield curve.
Spectroscopy with β2p and β-ν recoil shifts
9 pages, 4 figures.-- Printed version published Apr 22, 2002.
Beta-decay strength and isospin mixing studies in the sd and fp-shells
We have studied beta decays of MT<0 nuclei in sd and fp shells. The decay of 41Ti shows a large, 10(8) %, isospin mixing of IAS and the Gamow-Teller strength is observed to be quenched by a factor of q2=0.64. These results can be reproduced qualitatively in our shell model calculations. We have observed for the first time proton and gamma decay of the isobaric analogue state in 23Mg. Our results on the isospin mixing of the isobaric analogue state agrees well with the shell model calculations. The obtained proton branch of the IAS is used to extract the transition strength for the reaction 22Na(p,γ)23Mg.
Decays of theY97isomers to the single neutron nucleusZr97
The decays of the 9/2(+) and of the three-quasiparticle high spin isomer in Y-97 have been investigated following on-line mass separation with the ion-guide technique. Spins and parities for several of the lowest-lying levels in the daughter nucleus Zr-97 are revised and configurations are proposed. In particular, the 2264 keV level is identified as the h(11/2) single-neutron level. The population of a cascade on top of the h(11/2) level provides evidence for Gamow-Teller beta decay of the high-spin Y-97 isomer. Levels and transition rates are qualitatively well reproduced by regarding Zr-97 as a single-neutron nucleus with respect to the doubly closed Zr-96 core.
High-resolution study of the beta decay of 41Ti
Abstract An improved high-resolution study of the beta decay of 41 Ti, produced in the 40 Ca( 3 He, 2n) reaction at 40 MeV, has been performed at the Ion Guide Isotope Separator On-Line (IGISOL) facility. The beta-delayed radiation was detected by a low-energy charged-particle detector and a large Ge detector for gamma rays. The experimental beta-decay strength and its distribution, extracted from delayed-proton data, are compared with results of shell-model calculations in the sdfp space. The lowest J π = 3 2 + , T = 3 2 state in 41 Sc, the isobaric analogue state of the 41 Ti ground state, is estimated to contain 10% isospin impurity.
Improved ion guide for heavy-ion fusion-evaporation reactions
The ion guide for heavy-ion-induced reactions developed originally for the SARA facility in Grenoble has been implemented at the Jyvaskyla IGISOL facility. For the Cd-116(Ar-40, 6n)Dy-150 reaction an efficiency of 0.5% relative to the number of reaction products entering the stopping chamber was obtained. This is 3.5 times higher than previously obtained at SARA and corresponds to a yield of about 100 ions/(p mu C mb). Mass-separated yields for the Ar-36 + Mo-92 and Ar-36 + Mo-94 reactions were measured. (C) 1998 Elsevier Science B.V. All rights reserved.
First observation of nonyrast levels inZr103and level systematics ofN= 63 Sr, Zr, and Mo isotones
The {beta} decay of the very-neutron-rich nucleus {sup 103}Y has been studied at the isotope separator IGISOL, allowing for the first time the observation of nonyrast levels in its daughter {sub 40}{sup 103}Zr{sub 63}. The level structure is similar to that of its isotones {sup 101}Sr and {sup 105}Mo, suggesting a large ground-state deformation of {beta}{approx_equal} 0.4. Level systematics allows for new level assignments in both {sup 103}Zr and {sup 105}Mo. {copyright} {ital 1996 The American Physical Society.}
Two-proton decay of the isobaric analogue state of Ar-31
8 pages, 1 table, 4 figures.-- Journal issue title: "Nucleus-Nucleus Collisions".
First measurement of radioisotopes by collinear laser spectroscopy at an ion-guide separator
The first successful application of an ion-guide separator (IGISOL) for collinear laser spectroscopy of radioisotopes has achieved an efficiency comparable with the best obtained with catcher-ionizer facilities. The ion beam energy spread was determined to be less than 6 eV, allowing laser fluorescence resonance signals for the Ba-140,Ba-142,Ba-144 radioisotopes to be detected with high resolution and sensitivity. Applications of this technique to measuring nuclear properties of refractory elements and short lived isomers promises to be particularly advantageous.
Beta decay of very neutron-rich110Mo studied at the new IGISOL facility
The decay of the new activity110Mo (t1/2=0.30(4).s) has been observed at the new IGISOL separator. Multiscaled singles,β-γ-t and γ-y-t coincidences were recorded. The decay scheme suggests Iπ=2+ for the ground state of the daughter nucleus110Tc. Three 1+ levels are fed with logft values below 5, indicating no drastic change among Mo and Ru decays at the middle of the neutron shell. This experiment confirms the expectation that the new IGISOL facility will allow the identification of one or two new more neutron-rich isotopes per element in this region.
Superasymmetric fission at intermediate energy and production of neutron-rich nuclei with A < 80
Abstract The yields of neutron-rich Ni, Cu, Zn, Ga and Ge-isotopes were measured in 25 MeV proton induced fission of 238 U using the ion guide-based isotope separator technique. The results indicate enhancement for superasymmetric mass division at intermediate excitation energy of the fissioning nucleus and show the potential of this reaction for the production of neutron-rich exotic nuclei around Z = 28.
A thirty second isomer in Hf
An isomer has been detected in Hf-171 with a half-life of T-1/2 = 29.5(9) s. The state was populated in the Yb-170(alpha,3n)Hf-171m reaction at a beam energy of E-alpha = 50 MeV in an on-line ion guide isotope separator. The isomeric Hf-17lm(+) beam was extracted from the ion guide, mass-analysed and implanted in the surface of a microchannel-plate. The half-life of the collected activity was measured from the decay of the microchannel-plate count rate. We associate the isomer with the first excited slate in Hf-171 with spin 1/2(-) at an excitation energy of 22(2) keV.
Decays of T Z = − 3/2 nuclei 23Al, 31Cl, and 41Ti
This article gives an overview on the decay spectroscopy of T Z = − 3/2 nuclei 23Al, 31Cl, and 41Ti performed at the Ion Guide Isotope Separator On-Line (IGISOL) facility. The results of the IGISOL experiments are compared to the experimental results that have been published since. The isobaric multiplet mass equation (IMME) has been studied for the T = 3/2 quartets at A = 23 and A = 31. For 41Ti, a detailed comparison to the Gamow–Teller strengths obtained for the analog transitions via charge-exchange reactions has been done. Further improvements in the experimental instrumentation and methods and possible implementations for studying T Z = − 3/2 nuclei at the new IGISOL facility are di…