Axial and triaxial degrees of freedom in 72Zn

The unstable
𝑁
=
42
nucleus 72Zn has been studied using multiple safe Coulomb excitation in inverse kinematics. The experiment was performed at the REX-ISOLDE facility at CERN making first use of the silicon detector array C-REX in combination with the γ-ray spectrometer Miniball. The high angular coverage of C-REX allowed to determine the reduced transition strengths for the decay of the yrast
0
1
+
,
2
1
+
and
4
1
+
as well as of the
0
2
+
and
2
2
+
states in 72Zn. The quadrupole moments of the
2
1
+
,
4
1
+
and
2
2
+
states were extracted. Using model independent quadrupole invariants, the ground state of 72Zn was found to have an average deformation in the γ degree of freedom close to maximum triaxiality. In comparison to experimental data in zinc isotopes with
𝑁
<
40
, the collectivity of the
4
1
+
state in neutron-rich 72Zn is significantly larger, indicating a collective yrast band based on the ground state of 72Zn. In contrast, a low experimental
𝐵
(
𝐸
2
;
0
2
+
→
2
1
+
)
strength was determined, indicating a different structure for the
0
2
+
state. Shell-model calculations propose a
0
2
+
state featuring a larger fraction of the (spherical)
𝑁
=
40
closed-shell configuration in its wave function than for the
0
1
+
ground state.
The results were also compared with beyond mean field calculations which corroborate the large deformation in the γ degree of freedom, while pointing to a more deformed
0
2
+
state. These experimental and theoretical findings establish the importance of the γ degree of freedom in the ground state of 72Zn, located between the 68,70Ni nuclei that have spherical ground states, and 76Ge, which has a rigid triaxial shape.

Authors: S. Hellgartner, D. Mücher, K. Wimmer, V. Bildstein, J.L. Egido, R. Gernhäuser, R. Krücken, A.K. Nowak, M. Zielińska, C. Bauer, M.L.L. Benito, S. Bottoni, H. De Witte, J. Elseviers, D. Fedorov, F. Flavigny, A. Illana, M. Klintefjord, T. Kröll, R. Lutter, B. Marsh, R. Orlandi, J. Pakarinen, R. Raabe, E. Rapisarda, S. Reichert, P. Reiter, M. Scheck, M. Seidlitz, B. Siebeck, E. Siesling, T. Steinbach, T. Stora, M. Vermeulen, D. Voulot, N. Warr, F.J.C. Wenander

Doi: 10.1016/j.physletb.2023.137933 Get rights and content

Issue number:

Journal: Phys. Lett. B

Page number: 137933

Published on: 2023-04-26

Year: