Nuclear-Structure Calculations forCr52and Even Ni Isotopes

Abstract

Employing ${\mathrm{Ca}}^{48}$ and ${\mathrm{Ni}}^{56}$ as cores for ${\mathrm{Cr}}^{52}$ and ${\mathrm{Ni}}^{60}$, respectively, the shell-model properties of these nuclei are described using the renormalized reaction matrix elements of the Hamada-Johnston nucleon-nucleon potential. For ${\mathrm{Cr}}^{52}$, the seniorities 2 and 4 of the ${{f}_{\frac{7}{2}}}^{4}$ configuration are mixed through intermediate states of other configurations in an attempt to explain the branching ratios from $J=6$ and $J=5$ levels to the low-lying $J=4$ levels; and also the effect of increasing the configuration space is explicitly studied. A qualitative agreement between the calculated and experimental spectra is found, and the wave functions thus obtained are not found to be suitable for the description of transition rates. For ${\mathrm{Ni}}^{60}$, the effect of including the additional ${g}_{\frac{9}{2}}$ orbital is also investigated. The calculated energy levels agree fairly well with the experimental levels, but the wave functions do not provide a satisfactory explanation for the observed transition rates. The even Ni isotopes are then described in the framework of the modified Tamm-Dancoff approximation (MTDA). The agreement for the energy levels for ${\mathrm{Ni}}^{60}$ between the shell-model and the MTDA results is of the same quality, but the MTDA result indeed shows an improvement over the shell-model results in describing the vibrational characteristic of the second excited ${2}^{+}$ state. The MTDA results for Ni isotopes appear to be fairly satisfactory.