With the use of the 58Ni+S~ fusion-evaporation reaction and chemically selective on-line mass separation, the EC//3 + decay of t~ was studied by ?-ray and conversionelectron spectroscopy. In the course of these studies, a new 15.7-s isomeric state of t~ was observed. Reinvestigation of the {/-decays of the two heavier even isotopes of tin, produced in the s 8Ni + 58Ni reaction and mass separated without chemical discrimination, brought new information on the decay of l~ and ~~ The QEc values of 1~ l~ and 1~ were determined to be 4550 +300 keV, 3200+100 keV and -250 <2270 keV, respectively. In the data analysis, the emphasis is put on the identification of the 0+-~ 1 + Gamow-Teller /~ transitions and determination of their strengths. For 1~176 the total Gamow-Teller strengths are measured to be 20% to 30% of that predicted by the single-particle shell model with the inclusion of pairing correlations and core polarization. Predictions of the decay properties of the as yet unobserved ~~ and l~176 are made. 23.40.Hc; 21.10.Dr; 21.10.Pc; 27.60. +j; 29.30.Kv PACS: IntroductionThis paper presents a reinvestigation of the 104, 106,1088n EC/fl+ decays carried out at the GSI mass separator on-line to the UNILAC with the application of nuclear spectroscopy techniques. In the data analysis, the emphasis is put on the identification of the 0+~ 1 + Gamow-Teller (GT) transitions and determination of their strengths. The observation of more than one GT transition in each of the three decays, and the origin of quenching of the summed GT strengths compared to prediction of the extremesingle-particle shell model (ESPSM) are discussed with reference to theoretical studies [1][2][3].The main new results are those obtained for A = 104. Compared to our preceding investigation of the isotope ~~ [4,5] (see also the Leuven results * This work is part of the Ph.D. thesis of G.-E. Rathke[6]), an essential progress in studying its decay properties has been achieved due to the application of a mass-separator ion source [7,8] which allows for a substantial suppression of the isobaric contamination. Also the application of a mini-orange spectrometer [-9] for measuring the spectra of internal-conversion electrons appeared to be a very important addition to our 7-ray studies. As a result, the l~ --+ 1~ decay scheme is constructed with four wellestablished GT transitions.Four GT transitions (two of which were not reported in [10,11]) have also been observed in the 1~ decay. The previous version of the 1~ decay scheme [12, 13] has essentially been confirmed with respect to GT strength. Finally, the results of the present work have been extrapolated to get an estimate of the decay properties for the yet unobserved isotopes 1~and doubly magic l~176
For the first time, detailed decay-spectroscopic investigations were performed for the very neutron-deficient N=50 nuclide 9SCd. The 9SCd activity was produced in spallation reactions between 600 MeV protons and a natural tin target, yielding a 9SCd beam intensity of 10 to 60 atoms/s at the collector of the ISOLDE massseparator. By means of 7-ray and conversion-electron spectroscopy, 19 transitions were found to follow the /?+/EC decay 98Cd--*9SAg. The transitions at 61 and 107 keV were shown to be M 1(+ E 2) and E2, respectively, and the 98Cd half-life was measured as 9.2+0.3s. The QEC value of 9SCd is determined semiempirically and is compared to model predictions together with the measured QEc values of the neighbouring cadmium isotopes 1~176176 and the N=50 isotones 92M0, 94Ru, and 96pd, taken from the literature. The newly established decay scheme of 98Cd includes 9 excited states of 98Ag. Four states at 1691, 1861, 2164, and 2544 keV are directly fed by 0"~ 1 + Gamow-Teller beta transitions with a summed strength +0 s of 3.5-o17. This value corresponds to 25_+5% of the strength predicted for the GT transformation of a g9,2 proton (in 98Cd) into a g7/2 neutron (in 98Ag) by the extreme single-particle shell model. The GT-strength splitting and quenching, observed for 98Cd, are compared with the corresponding data for lighter even-even N = 50 isotones, and are discussed with reference to the predictions of more sophisticated nuclear models. We find that only in some cases it is possible to explain qualitatively the observed GT strength distribution and its total magnitude without renormalizing the free-neutron value of the axial-vector coupling constant.
In the N = 83 nucleus ~ 5 ~Er we observed the isomeric E 3 transition in conversion electron measurements following on-line mass separation and located its 0.6 s 27/2-isomer at 2.586 MeV. Gamma-ray data establish a 4.7(3)% Gamow-Teller/?-decay branch proceeding to high-spin states above 2 MeV excitation in '51Ho. A weak /?-decay branch of 0.7(3)% was also observed for the 0.5 s 27/2-isomer in the 149Dy isotone, and it was established that a similar 27/2-E3-isomer does not occur in 153yb. First results on the 1 s 1Tm and 151Er ground-state/?-decays are briefly discussed.
Neutron-deficient isotopes of cadmium were produced in the p(600 MeV)+natSn spaltation reaction. The ISOLDE facility provided mass-separated beams of these isotopes. The production yield was 103 to 104 atoms/s for l~176 and roughly two orders of magnitude less for 98Cd. The properties of the ~~176176176 decay were studied in detail by X-ray, y-ray and conversion electron spectroscopy. Forty nine y-transitions were assigned to this decay, and all but five of them were placed in the decay scheme. The half-life was determined to be 49.1+0.5 s. The QEC value of 3890+70keV was deduced from a comparison of experimental and theoretical /?+/(EC+/~ +) probability ratios. Seven 0+--*1 + Gamow-Teller transitions with log ft values between 3.5 and 4.9 were identified. The total (summed) strength is about five times smaller than predicted by the shell model for the transformation of a g9/2 proton into a g7/2 neutron. The quenching of the Gamow-Teller strength and other questions of nuclear structure are discussed for the ~~176 decay. The properties of 98Cd are inferred by extrapolation of 1~176176176 data, and some preliminary experimental results on 98Cd decay are presented.
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