Single-particle and collective excitations in ${}^{66}\mathrm{Zn}$

Single-particle and collective excitations in ${}^{66}\mathrm{Zn}$ have been investigated via the multinucleon transfer reaction, ${}^{26}\mathrm{Mg}({}^{48}\mathrm{Ca}$, $\alpha 4n\gamma$) using the Gammasphere multidetector array and the Fragment Mass Analyzer. In addition to confirming and complementing the previously known low-spin structure, a new quasirotational band comprising several stretched $E2$ transitions has been established to high spins. However, due to fragmentary nature of its decay, it was not possible to link this sequence to the low-lying states and, thus, determine the absolute excitation energies, spins, and parities unambiguously. Large-scale shell-model calculations employing the JUN45 and jj44b effective interactions are able to successfully describe the low-spin structure and herewith confirm that it is dominated by single-particle excitations. The newly established rotational cascade is compared with known superdeformed bands in the $A\approx 60\text{–}70$ mass region, and with results of calculations performed within the frameworks of the cranked shell model and the adiabatic and configuration-fixed constrained covariant density functional theory and the quantum particle-rotor model.

Figure 1

Angular distributions for some of the $\gamma$ transitions shown in the ${}^{66}\mathrm{Zn}$ level scheme. Experimental data are shown as black circles while the angular distribution fit is given as a red curve.

Figure 2

Level scheme of ${}^{66}\mathrm{Zn}$ as observed in the present study. The placement of Band 1 is schematic since the absolute excitation energy, spin, and parity are unknown; see text for further details.

Figure 3

Total background corrected projection spectrum obtained for ${}^{66}\mathrm{Zn}$.

Figure 4

Coincidence gate on the 738-keV transition.

Figure 5

Sum of single coincidence gates placed on $\gamma$-ray transitions in band 1. Pertinent $\gamma$ rays are highlighted in red.

Figure 6

Coincidence spectra obtained by single gating on transitions at (a) 1432 keV and (b) 1832 keV. Members of the rotational band are marked in red.

Figure 7

Experimental level energies in ${}^{66}\mathrm{Zn}$ compared with spherical shell-model calculations using the jj44b and JUN45 effective interactions. The yrast levels are indicated by the red lines while the negative structure is colored dark blue.

Figure 8

Comparison of the yrast level energies in ${}^{66}\mathrm{Zn}$ with spherical shell-model states calculated using the jj44b and JUN45 effective interactions (see text for details).

Figure 9

Angular momentum as a function of transition energy for the superdeformed bands in ${}^{60}\mathrm{Zn}$, ${}^{68}\mathrm{Zn}$, and ${}^{68}\mathrm{Ge}$ compared with the newly established band in ${}^{66}\mathrm{Zn}$. The data for ${}^{68}\mathrm{Ge}$ and ${}^{66}\mathrm{Zn}$ are plotted for band head spins of $I_0=14$ and $I_0=16$, and $I_0=12$ and $I_0=14$, respectively (see text for details).

Figure 10

Comparison of the rotational band in ${}^{66}\mathrm{Zn}$ with the SD sequence in ${}^{68}\mathrm{Ge}$. The data for ${}^{68}\mathrm{Ge}$ are taken from Ref. [12].

Figure 11

Variation of the experimentally deduced dynamic moment of inertia as a function of the rotational frequency $\left(\hslash \omega \right)$ for Band 1 in ${}^{66}\mathrm{Zn}$ (present work), compared with known SD bands in the neighboring ${}^{68}\mathrm{Ge}$ [12] and ${}^{60,68}\mathrm{Zn}$ [3, 6].

Figure 12

The calculated quasiproton Routhian $\left(e^{\prime }\right)$ as a function of rotational frequency $\left(\hslash \omega \right)$. The following convention is adopted for the parity and signature $(\pi ,\alpha )$ of the Routhians: $(+,0)$ solid lines, $(+,1)$ dotted lines, $(-,0)$ dash-dotted lines, and $(-,1)$ dashed lines.

Figure 13

Energy as a function of spin for the rotational band (Band 1) in ${}^{66}\mathrm{Zn}$ calculated by particle rotor model in comparison with the experimental data.

Figure 14

The root mean square components along the medium ($m$), short ($s$), and long ($l$) axis of the core $R_k={\langle {\widehat{R}}_k^2\rangle }^{1/2}$, the active protons $J_{\pi k}={\langle {\widehat{j}}_{pk}^2\rangle }^{1/2}$, and the total nuclear system $I_k={\langle {\widehat{I}}_k^2\rangle }^{1/2}$ as function of spin calculated by means of particle rotor model for the Band 1 in ${}^{66}\mathrm{Zn}$.