Statistical and non-statistical $\gamma$-decay properties of ${}^{64}$Zn

Abstract

We present a study on the $\gamma$-decay properties of ${}^{64}$Zn using the Oslo method on ${}^{64}$Zn($p,p^{\prime }\gamma$) data combined with ${}^{64}$Zn$(\gamma ,n)$ cross-section measurements at the NewSUBARU facility. With the Oslo method, we have measured the $\gamma$-ray strength function ($\gamma$SF) and the nuclear level density (NLD) below the neutron threshold. We observe that the NLD trend in the quasi-continuum region of ${}^{64}$Zn is best characterized by a constant-temperature-like model. %with temperature parameter $T_{\mathrm{CT}}=1.21(5)$ MeV. Surprisingly, we find that $\gamma$-ray transitions from the quasi-continuum decaying directly to the $0^{+}$ ground state seem to be strongly hindered with a hindrance factor of $\kappa \approx 0.5$, which could be an indication of non-statistical effects in the ground-state decay due to, \textit{e.g.}, differences in nuclear shapes. For $\gamma$ energies above the neutron separation energy, the NewSUBARU ($\gamma ,n$) data set probes a significant part of the giant dipole resonance. Furthermore, we find that the Oslo-method $\gamma$SF shows a rather smooth behavior, with a clear low-energy enhancement (LEE) for $E_{\gamma }<4$ MeV.

19 pages, 24 figures, submitted to Phys. Rev. C