Coulomb Excitation of Neutron-Rich Zn Isotopes: First Observation of the $2_1^{+}$ State in ${}^{80}\mathrm{Zn}$

Neutron-rich, radioactive Zn isotopes were investigated at the Radioactive Ion Beam facility REX-ISOLDE (CERN) using low-energy Coulomb excitation. The energy of the $2_1^{+}$ state in ${}^{78}\mathrm{Zn}$ could be firmly established and for the first time the $2^{+}\to 0_1^{+}$ transition in ${}^{80}\mathrm{Zn}$ was observed at 1492(1) keV. $B(E2,2_1^{+}\to 0_1^{+})$ values were extracted for ${}^{74,76,78,80}\mathrm{Zn}$ and compared to large scale shell model calculations. With only two protons outside the $Z=28$ proton core, ${}^{80}\mathrm{Zn}$ is the lightest $N=50$ isotone for which spectroscopic information has been obtained to date. Two sets of advanced shell model calculations reproduce the observed $B(E2)$ systematics. The results for $N=50$ isotones indicate a good $N=50$ shell closure and a strong $Z=28$ proton core polarization. The new results serve as benchmarks to establish theoretical models, predicting the nuclear properties of the doubly magic nucleus ${}^{78}\mathrm{Ni}$.

Figure 1

Doppler corrected for the detected beam particle and random subtracted $\gamma$ spectra during laser-ON periods, gated by detected ${}^{78}\mathrm{Zn},\mathrm{Ga}$ (a) and ${}^{80}\mathrm{Zn},\mathrm{Ga},\mathrm{Rb}$ (b) particles. The filled symbols indicate $\gamma$ lines following Coulomb excitation of the dominant isobaric contaminants ($\mathrm{\text{circles}}={}^{80}\mathrm{Rb}$, $\mathrm{\text{square}}={}^{78}\mathrm{Ga}$).

Figure 2

$E(2_1^{+})$ and $B(E2)\downarrow$ systematics for Ni ($Z=28$), Zn ($Z=30$), and Ge ($Z=32$) isotopes. $B(E2)\downarrow$ values were taken from Refs. 6, 7, 9, 10, 18, 30. The dashed and dotted lines correspond to SM calculations for Zn isotopes.

Figure 3

$E(2_1^{+})$ and $B(E2)$ values for $N=50$ isotones. The dashed and dotted lines correspond to SM calculations.