Shell structure of collective states inFe56,Fe58, andFe60

Abstract

Conventional shell-model calculations of the iron isotopes with $A=56\ensuremath{-}60$ are discussed. The calculated level spectra are in good agreement with experiment. The calculations of $E2$ observables are in reasonable agreement with experiment when added effective charges of $1.0e$ are used for both neutrons and protons. The neutron effective charge is significantly different from one appropriate ($1.9e$) for $^{56}\mathrm{Ni}$. There is a strong state dependence in the effective $M1$ operator, and calculations of $M1$ observables are in general disagreement with experiment. An analysis of the structure of ground-state bands and yrast levels is made in terms of a simple rotational model. In all even isotopes, the intrinsic quadrupole moments in the ground-state "band" shrink dramatically with increasing $J$. There is evidence of a band crossing in all three even isotopes, but no evidence is found for an abrupt shape change in the ground-state bands of these nuclei. It is concluded that no simple rotational model gives a good description of the low-lying states of the iron isotopes.NUCLEAR STRUCTURE $^{56}\mathrm{Fe}$, $^{57}\mathrm{Fe}$, $^{58}\mathrm{Fe}$, $^{59}\mathrm{Fe}$, $^{60}\mathrm{Fe}$, calculated levels. $^{56}\mathrm{Fe}$, $^{58}\mathrm{Fe}$, $^{60}\mathrm{Fe}$, calculated $B(M1)$, $B(E2)$, $\ensuremath{\mu}$, branching ratios. Shell model, Vervier interaction, Horie-Ogawa interaction, effective operators. Comparison with experiment and rotational model.