Abstract
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 70Se , where no coexistence has yet been identified.
Purpose: To determine the presence or absence of any low-lying 0+ state in 70Se, 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 70Se . 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: 70Se
does not have a well-defined axial shape. The 2+2 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.
Purpose: To determine the presence or absence of any low-lying 0+ state in 70Se, 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 70Se . 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: 70Se
does not have a well-defined axial shape. The 2+2 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.
| Original language | English |
|---|---|
| Article number | 024318 |
| Number of pages | 16 |
| Journal | Physical Review C |
| Volume | 110 |
| Issue number | 2 |
| DOIs | |
| Publication status | Published - 20 Aug 2024 |