Yazar "Smith, J. F." seçeneğine göre listele

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    Evolution of nuclear structure in the neutron-rich 96,97,99Nb isotopes: Evidence for shape coexistence in N=58 99Nb
    (Amer Physical Soc, 2023) Kumar, V.; Chapman, R.; O'Donnell, D.; Ollier, J.; Orlandi, R.; Smith, J. F.; Spohr, K. -m.
    Excited states of the neutron-rich niobium isotopes 96,97,98,99 41Nb have been populated in two experiments which used fusion-fission and multinucleon binary grazing reactions to populate high-spin yrast states. 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 the associated gamma rays were detected using the CLARA array of Ge detectors. In the second experiment, the GASP array of escape-suppressed Ge detectors was used to detect gamma rays from fusion-fission products formed following the interaction of a 230-MeV beam of 36S ions with a thick target of 176Yb. Level schemes of 96,97,99Nb were established up to excitation energies of 4545, 5409, and 3814 keV, respectively; states with proposed spin values up to about 15 h over bar were populated. Gamma-ray photopeaks corresponding to transitions in 98Nb were also observed in the PRISMA-CLARA experiment; however, it was not possible, in this case, to produce a level scheme based on gamma-ray coincidence data from the GASP experiment. For 96Nb and 97Nb, the level schemes are in agreement with the results of earlier publications. Two new decay sequences have been populated in 99Nb; tentative J pi values of the hitherto unobserved states have been assigned through comparisons with J pi values of neighboring nuclei. In contrast with earlier published studies of the high-spin spectroscopy of 96Nb and 97Nb, the present work provides an unambiguous association of the observed gamma rays with the A and Z of the excited nucleus. The structure of the yrast states of 96,97,99Nb is discussed within the context of shell-model calculations. The experimental results, supported by model calculations, indicate the first observation of shape coexistence at low spin and low excitation energy in the N = 58 nucleus 99Nb. The results of TRS calculations indicate that the 9/2+ ground state is triaxial, tending to oblate shapes with a transition to a more deformed prolate shape beyond the 17/2+ member of the decay sequence; here the sequence has been observed to (29/2+). On the other hand, the previously unobserved decay sequence based on the 5/2- state at 631 keV exhibits the characteristics of a rotational sequence and has been assigned Nilsson quantum numbers 5/2-[303]. TRS calculations indicate that the 5/2-[303] band is gamma soft and this is consistent with the inability of the particle-rotor model to reproduce the observed behavior of the signature-splitting function.
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    Öğe
    Spectroscopic study of 97 Mo, 99 Mo, and 101 Mo
    (Amer Physical Soc, 2024) Kumar, V.; Chapman, R.; Ollier, J.; Orlandi, R.; Smith, J. F.; Spohr, K. -m.; Torres, D. A.
    Excited states of the molybdenum isotopes 97,99,101 42 Mo 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 gamma 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 gamma rays were detected using the CLARA array of escape-suppressed Ge detectors. In 99Mo, the previously known positive-parity vd5/2 decay sequence was extended to spin (25/2+) while, in 101Mo, a similar, but hitherto unobserved vg7/2 positive-parity decay sequence was established to spin (27/2+). In 99Mo and in 101Mo, previously observed vh11/2 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 h11/2 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 vh11/2 negative-parity decay sequences of the three isotopes studied here, model-dependent evidence is presented for nuclear shape changes with increasing neutron number.