Band crossing observed in neutron-rich Pd isotopes via spontaneous fission of 252Cf.

Abstract

High spin excited states in neutron-rich nuclei $^{112,114,116}\mathrm{Pd}$ have been investigated by measuring prompt \ensuremath{\gamma} rays emitted from a $^{252}\mathrm{Cf}$ spontaneous fission source. Two different measurements were performed. First, \ensuremath{\gamma}-\ensuremath{\gamma} coincidence data, necessary to determine the decay schemes, were obtained by using an array of 20 Compton-suppressed Ge detectors. Second, Z identification and the enhancement of a desired neutron channel were carried out using a x-n-\ensuremath{\gamma} multiplicity spectrometer. Ground state bands have been extended to ${\mathit{J}}^{\mathrm{\ensuremath{\pi}}}$=${10}^{+}$ for $^{112}\mathrm{Pd}$, and ${\mathit{J}}^{\mathrm{\ensuremath{\pi}}}$=${12}^{+}$ for $^{114}\mathrm{Pd}$ and $^{116}\mathrm{Pd}$. Band crossings were observed in all three isotopes. It was found from cranked shell model calculations that these backbends are due to the alignment of two ${\mathit{g}}_{9/2}$ protons. The measured energy levels were also compared with predictions of the interacting boson model.