Reevaluation of structures in Se 70 from combined conversion-electron and γ -ray spectroscopy

TY - JOUR

T1 - Reevaluation of structures in Se 70 from combined conversion-electron and γ -ray spectroscopy

AU - Smallcombe, J.

AU - Garnsworthy, A. B.

AU - Korten, W.

AU - Singh, P.

AU - Muir, D.

AU - Próchniak, L.

AU - Ali, F. A.

AU - Andreoiu, C.

AU - Ansari, S.

AU - Ball, G. C.

AU - Barton, C. J.

AU - Bhattacharjee, S. S.

AU - Bowry, M.

AU - Briscoe, A. D.

AU - Caballero-Folch, R.

AU - Chester, A.

AU - Gillespie, S. A.

AU - Grinyer, G. F.

AU - Hackman, G.

AU - Heery, J.

AU - Jones, C.

AU - Melon, B.

AU - Moukaddam, M.

AU - Nannini, A.

AU - Ruotsalainen, P.

AU - Starosta, K.

AU - Svensson, C. E.

AU - Wadsworth, R.

AU - Williams, J.

N1 - Publisher Copyright: © 2024 authors. Published by the American Physical Society.

PY - 2024/8/20

Y1 - 2024/8/20

N2 - Background: In the selenium isotopes various shape phenomena are present, in particular, the emergence of a dominant oblate deformation in the most neutron-deficient isotopes has been observed. The scenario of shape coexisting oblate and prolate bands has been proposed across the isotopic chain, with the crossing point of such bands being located near Se70, where no coexistence has yet been identified. Purpose: To determine the presence or absence of any low-lying 0+ state in Se70, confirm the level structure, and interpret the nuclear deformation with theoretical models. Methods: A combined internal-conversion-electron and γ-ray spectroscopy study was undertaken with the SPICE and TIGRESS spectrometers at the TRIUMF-ISAC-II facility. Nuclear models were provided by the generalized triaxial rotor model (GTRM) and the collective generalised Bohr Hamiltonian (GBH). Results: Despite a comprehensive search, no evidence was found for the existence of a 0+ state below 2 MeV in Se70. Significant discrepancies to the previously established positive-parity-level scheme were found. GBH calculations using UNEDF1 mass parameters were found to reproduce the revised low-lying level structure well. Conclusion:Se70 does not have a well-defined axial shape. The 22+ state at 1601 keV resembles a quasi-γ excitation rather than a member of a shape coexisting band; the presence of such a band is all but ruled out.

AB - Background: In the selenium isotopes various shape phenomena are present, in particular, the emergence of a dominant oblate deformation in the most neutron-deficient isotopes has been observed. The scenario of shape coexisting oblate and prolate bands has been proposed across the isotopic chain, with the crossing point of such bands being located near Se70, where no coexistence has yet been identified. Purpose: To determine the presence or absence of any low-lying 0+ state in Se70, confirm the level structure, and interpret the nuclear deformation with theoretical models. Methods: A combined internal-conversion-electron and γ-ray spectroscopy study was undertaken with the SPICE and TIGRESS spectrometers at the TRIUMF-ISAC-II facility. Nuclear models were provided by the generalized triaxial rotor model (GTRM) and the collective generalised Bohr Hamiltonian (GBH). Results: Despite a comprehensive search, no evidence was found for the existence of a 0+ state below 2 MeV in Se70. Significant discrepancies to the previously established positive-parity-level scheme were found. GBH calculations using UNEDF1 mass parameters were found to reproduce the revised low-lying level structure well. Conclusion:Se70 does not have a well-defined axial shape. The 22+ state at 1601 keV resembles a quasi-γ excitation rather than a member of a shape coexisting band; the presence of such a band is all but ruled out.

UR - http://www.scopus.com/inward/record.url?scp=85201746249&partnerID=8YFLogxK

U2 - 10.1103/PhysRevC.110.024318

DO - 10.1103/PhysRevC.110.024318

M3 - Article

AN - SCOPUS:85201746249

SN - 2469-9985

VL - 110

JO - Physical Review C

JF - Physical Review C

IS - 2

M1 - 024318

ER -