E2 Transition Probabilities for Decays of Isomers Observed in Neutron-rich Odd Sn Isotopes

Iskra, Ł. W.; Broda, R.; Janssens, R. V. F.; Wrzesiński, J.; Chiara, C. J.; Carpenter, M. P.; Fornal, B.; Hoteling, N.; Kondev, F. G.; Królas, W.; Lauritsen, T.; Pawłat, T.; Seweryniak, D.; Stefanescu, I.; Walters, W. B.; Zhu, S.

doi:10.5506/aphyspolb.46.651

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“…The analysis of gamma-ray coincidence relationships, presented in Refs. [10,16,17], established unambiguously that, in the 48 Ca + 238 U and 48 Ca + 208 Pb systems, the Sn isotopes of interest were predominantly produced in fusion-fission reactions while, in the 64 Ni + 238 U reaction, the same nuclei were populated through fission of the 238 U target or of target-like products. The relative populations of the known 27/2 − isomers were extracted from the coincidence data and are compared in Fig.…”

Section: Experimental Procedures and Data Analysismentioning

confidence: 98%

Shell-model states with seniorityν=3, 5, and 7 in odd-Aneutron-rich Sn isotopes

et al. 2016

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Excited states with seniority ν = 3, 5, and 7 have been investigated in odd neutron-rich 119,121,123,125 Sn isotopes produced by fusion-fission of 6.9-MeV/A 48 Ca beams with 208 Pb and 238 U targets and by fission of an 238 U target bombarded with 6.7-MeV/A 64 Ni beams. Level schemes have been established up to high spin and excitation energies in excess of 6 MeV, based on multifold gamma-ray coincidence relationships measured with the Gammasphere array. In the analysis, the presence of isomers was exploited to identify gamma rays and propose transition placements using prompt and delayed coincidence techniques. 121 Sn, has now been confirmed. In both cases, isomeric half-lives were determined with good precision. In the range of ν = 3 excitations, the observed transitions linking the various states enabled one to propose with confidence spin-parity assignments for all the observed states. Above the 27/2 − isomers, an elaborate structure of negative-parity levels was established reaching the (39/2 − ), ν = 7 states, with tentative spin-parity assignments based on the observed deexcitation paths as well as on general yrast population arguments. In all the isotopes under investigation, strongly populated sequences of positive-parity (35/2 + ), (31/2 + ), and (27/2 + ) states were established, feeding the 23/2 + isomers via cascades of three transitions. In the 121,123 Sn isotopes, these sequences also enabled the delineation of higher-lying levels, up to (43/2 + ) states. In 123 Sn, a short half-life was determined for the (35/2 + ) state. Shell-model calculations were carried out for all the odd Sn isotopes, from 129 Sn down to 119 Sn, and the results were found to reproduce the experimental level energies rather well. Nevertheless, some systematic deviations between calculated and experimental energies, especially for positive-parity states, point to the need to improve some of the two-body interactions used in calculations. The computed wave-function amplitudes provide for a fairly transparent interpretation of the observed level structures. The systematics of level energies over the broad A = 117 -129 range of Sn isotopes displays a smooth decrease with mass A, and the observed regularity confirms most of the proposed spin-parity assignments. The systematics of the B(E2) reduced transition probabilities extracted for the 23/2 + and 19/2 + isomers is discussed with an emphasis on the close similarity of the observed A dependence with that of the E2 transition rates established for other ν = 2, 3, and 4 isomers in the Sn isotopic chain.

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Section: Experimental Procedures and Data Analysismentioning

confidence: 98%