Persistence of the $Z=28$ Shell Gap Around ${}^{78}\mathrm{Ni}$: First Spectroscopy of ${}^{79}\mathrm{Cu}$

In-beam $\gamma$-ray spectroscopy of ${}^{79}\mathrm{Cu}$ is performed at the Radioactive Isotope Beam Factory of RIKEN. The nucleus of interest is produced through proton knockout from a ${}^{80}\mathrm{Zn}$ beam at $270\mathrm{MeV}/\mathrm{nucleon}$. The level scheme up to 4.6 MeV is established for the first time and the results are compared to Monte Carlo shell-model calculations. We do not observe significant knockout feeding to the excited states below 2.2 MeV, which indicates that the $Z=28$ gap at $N=50$ remains large. The results show that the ${}^{79}\mathrm{Cu}$ nucleus can be described in terms of a valence proton outside a ${}^{78}\mathrm{Ni}$ core, implying the magic character of the latter.

Figure 1

$\gamma$-ray spectrum of ${}^{80}\mathrm{Zn}(p,2p){}^{79}\mathrm{Cu}$ after Doppler correction, with multiplicities below 4. The experimental data points are in black, with the double-exponential background as the blue dashed line, the simulated response function of each transition in purple, and the sum of the simulated response functions with the background in red. Discrepancies between the data and the fit are due to nonidentified transitions (see text). The inset shows $\gamma \text{−}\gamma$ coincidences after background subtraction for a gate set on the 656-keV [subpanel (a)] and 855-keV [subpanel (b)] transitions.

Figure 2

Proposed level scheme for ${}^{79}\mathrm{Cu}$. The experimental results (left) are compared to Monte Carlo shell-model (MCSM) calculations (right).

Figure 3

Systematics of the first ${3/2}^{-}$ and ${5/2}^{-}$ states in copper isotopes. Data taken from Refs. [30, 31, 35, 45, 46, 47] and this work. The error bars are smaller than the data points.