Status of vibrational structure inNi62

Abstract

Measurements consisting of $\ensuremath{\gamma}$-ray excitation functions and angular distributions were performed using the ($n,{n}^{\ensuremath{'}}\ensuremath{\gamma}$) reaction on $^{62}\mathrm{Ni}$. The excitation function data allowed us to check the consistency of the placement of transitions in the level scheme. From $\ensuremath{\gamma}$-ray angular distributions, the lifetimes of levels up to $~3.8$ MeV in excitation energy were extracted with the Doppler-shift attenuation method. The experimentally deduced values of reduced transition probabilities were compared with the predictions of the quadrupole vibrator model and with large-scale shell model calculations in the $\mathit{fp}$ shell configuration space. Two-phonon states were found to exist with some notable deviation from the predictions of the quadrupole vibrator model, but no evidence for the existence of three-phonon states could be established. $Z=28$ proton core excitations played a major role in understanding the observed structure.