%0 Journal Article
%T Persistence of the Z=28 shell gap in A=75 isobars: Identification of a possible (1/2(-)) μs isomer in Co-75 and beta decay to Ni-75
%A Escrig, S. et al
%A Morales, A. I.
%J Physical Review C
%D 2021
%V 103
%N 6
%I Amer Physical Soc
%@ 2469-9985
%G English
%F Escrig+Morales2021
%O WOS:000669040500001
%O exported from refbase (https://references.ific.uv.es/refbase/show.php?record=4887), last updated on Mon, 19 Jul 2021 06:56:55 +0000
%X Background: The evolution of shell structure around doubly magic exotic nuclei is of great interest in nuclear physics and astrophysics. In the 'southwest' region of Ni-78, the development of deformation might trigger a major shift in our understanding of explosive nucleosynthesis. To this end, new spectroscopic information on key close-lying nuclei is very valuable. Purpose: We intend to measure the isomeric and beta decay of Co-75, with one-proton and two-neutron holes relative to Ni-78, to access new nuclear structure information in Co-75 and its beta-decay daughters Ni-75 and Ni-74. Methods: The nucleus Co-75 is produced in relativistic in-flight fission reactions of U-238 at the Radioactive Ion Beam Factory in the RIKEN Nishina Center. Its isomeric and f decay are studied exploiting the BigRIPS and EURICA setups. Results: We obtain partial beta-decay spectra for Ni-75 and Ni-74, and report a new isomeric transition in Co-75. The energy [E-gamma = 1914(2) keV] and half-life [t(1/2) = 13(6) μs] of the delayed gamma ray lend support for the existence of aJ(pi) = (1/2(-)) isomeric state at 1914(2) keV. A comparison with PFSDG-U shell-model calculations provides a good account for the observed states in Ni-75, but the first calculated 1/2(-) level in Co-75, a prolate K = 1/2 state, is predicted about 1 MeV below the observed (1/2(-)) level. Conclusions: The spherical-like structure of the lowest-lying excited states in Ni-75 is proved. In the case of Co-75, the results suggest that the dominance of the spherical configurations over the deformed ones might be stronger than expected below Ni-78. Further experimental efforts to discern the nature of the J(pi) = (1/2(-)) isomer are necessary.
%R 10.1103/PhysRevC.103.064328
%U https://arxiv.org/abs/2101.06246
%U https://doi.org/10.1103/PhysRevC.103.064328
%P 064328-12pp