Level structure ofGe67and its implications for the general structure of nuclei in the1f−2pshell

Abstract

From the results of prompt and $\ensuremath{\beta}$-delayed $\ensuremath{\gamma}$-ray singles and $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidence measurements, twenty-four excited states and forty-six gamma transitions are identified in the level scheme of $^{67}\mathrm{Ge}$. Angular distributions and directional correlations of prompt $^{67}\mathrm{Ge}$ gamma rays have been measured to obtain the spins of the $^{67}\mathrm{Ge}$ ground state and excited states at 18.2, 122.7, 243.6, 711.3, and 1019.9 keV. Parities are assigned to the first five states on the basis of $\mathrm{fp}$ shell systematics and observed $^{67}\mathrm{Ge}$ gamma-ray branching ratios. The 752-keV excitation energy of the first ${\frac{9}{2}}^{+}$ level in $^{67}\mathrm{Ge}$ is determined from an excitation function for the $^{64}\mathrm{Zn}(\ensuremath{\alpha}, \mathrm{n}\ensuremath{\gamma})^{67}\mathrm{Ge}$ reaction. The angular distribution and correlation measurements also provide $\frac{E2}{M1}$ mixing ratios for the 104.4, 120.8, 122.7, 243.6, 589.0, and 897.5 keV $^{67}\mathrm{Ge}$ gamma rays. The level scheme of $^{67}\mathrm{Ge}$ and the corresponding schemes for $^{63,65}\mathrm{Ni}$, $^{65,67}\mathrm{Zn}$, and $^{69}\mathrm{Ge}$ are observed to have strong similarities at low excitation. Systematic trends in $E2$ transition rates are interpreted in the context of shell and collective features of the nuclei. It is found that models based on a single particle coupled to a vibrational or deformed core do not explain the observed systematics, and are an inaccurate representation of these nuclei. The systematics do agree with a many-nucleon shell model emphasizing the short-range pairing interaction and configuration mixing for the valence neutrons.NUCLEAR REACTIONS $^{64}\mathrm{Zn}(\ensuremath{\alpha}, \mathrm{n}\ensuremath{\gamma})$, $^{63}\mathrm{Cu}(^{6}\mathrm{Li}, 2\mathrm{n}\ensuremath{\gamma})$, $^{58}\mathrm{Ni}(^{14}\mathrm{N}, \ensuremath{\alpha}\mathrm{n})$; $^{67}\mathrm{Ge}$ level scheme, $E\ensuremath{\gamma}$, $\ensuremath{\gamma}(\ensuremath{\theta})$, $\ensuremath{\gamma}\ensuremath{\gamma}(\ensuremath{\theta})$, $\ensuremath{\delta}(\frac{E2}{M1})$, ${J}^{\ensuremath{\pi}}$. Directional correlations with an oriented source. Ge(Li) detectors, enriched targets. Nuclear systematics, nuclear deformation.