Spectroscopic study of ⁹⁷Mo, ⁹⁹Mo, and ¹⁰¹Mo

Excited states of the molybdenum isotopes ^97,99,101₄₂Mo have been populated in two experiments which used fusion-fission and binary grazing reactions to populate yrast states of the nuclei of interest. In the first experiment, the GASP array of escape-suppressed Ge detectors was used to detect 𝛾 rays from fusion-fission products initiated by the interaction of a 230-MeV beam of ³⁶S ions with a thick target of ¹⁷⁶Yb. In the multinucleon transfer experiment, a 530-MeV beam of ⁹⁶Zr ions was incident on a thin ¹²⁴Sn target; projectile-like ejectiles were detected and identified using the PRISMA magnetic spectrometer and their associated 𝛾 rays were detected using the CLARA array of escape-suppressed Ge detectors. In ⁹⁹Mo, the previously known positive-parity 𝜈⁢d_5/2 decay sequence was extended to spin (25/2⁺) while, in ¹⁰¹Mo, a similar, but hitherto unobserved 𝜈⁢g7/2 positive-parity decay sequence was established to spin (27/2+). In ⁹⁹Mo and in 101Mo, previously observed 𝜈⁢ℎ11/2 negative-parity decay sequences were also observed to spin 27/2⁻. Although the observed decay sequences in ⁹⁷Mo have not been extended beyond the results of earlier work, a disagreement in the published level structure of the ℎ_11/2 band has been resolved. The observed positive-parity decay sequences have been compared with the results of state-of-the-art shell-model calculations; the general features of the energy spectrum of excited states of ⁹⁷Mo, ⁹⁹Mo, and ¹⁰¹Mo are reproduced, but not in detail. The experimental energies of the negative-parity states of ⁹⁹Mo and ¹⁰¹Mo are reasonably well reproduced in particle-rotor (PRM) calculations. For ⁹⁷Mo, better agreement with the high-spin states was obtained when the core in the PRM calculations was treated in a variable moment of inertia approach. For the 𝜈⁢ℎ_11/2 negative-parity decay sequences of the three isotopes studied here, model-dependent evidence is presented for nuclear shape changes with increasing neutron number.