학술논문
First Evidence of Axial Shape Asymmetry and Configuration Coexistence in $^{74}$Zn: Suggestion for a Northern Extension of the $N=40$ Island of Inversion
Document Type
Working Paper
Author
Rocchini, M.; Garrett, P. E.; Zielinska, M.; Lenzi, S. M.; Dao, D. D.; Nowacki, F.; Bildstein, V.; MacLean, A. D.; Olaizola, B.; Ahmed, Z. T.; Andreoiu, C.; Babu, A.; Ball, G. C.; Bhattacharjee, S. S.; Bidaman, H.; Cheng, C.; Coleman, R.; Dillmann, I.; Garnsworthy, A. B.; Gillespie, S.; Griffin, C. J.; Grinyer, G. F.; Hackman, G.; Hanley, M.; Illana, A.; Jones, S.; Laffoley, A. T.; Leach, K. G.; Lubna, R. S.; McAfee, J.; Natzke, C.; Pannu, S.; Paxman, C.; Porzio, C.; Radich, A. J.; Rajabali, M. M.; Sarazin, F.; Schwarz, K.; Shadrick, S.; Sharma, S.; Suh, J.; Svensson, C. E.; Yates, D.; Zidar, T.
Source
Subject
Language
Abstract
The excited states of $N=44$ $^{74}$Zn were investigated via $\gamma$-ray spectroscopy following $^{74}$Cu $\beta$ decay. By exploiting $\gamma$-$\gamma$ angular correlation analysis, the $2_2^+$, $3_1^+$, $0_2^+$ and $2_3^+$ states in $^{74}$Zn were firmly established. The $\gamma$-ray branching and $E2/M1$ mixing ratios for transitions de-exciting the $2_2^+$, $3_1^+$ and $2_3^+$ states were measured, allowing for the extraction of relative $B(E2)$ values. In particular, the $2_3^+ \to 0_2^+$ and $2_3^+ \to 4_1^+$ transitions were observed for the first time. The results show excellent agreement with new microscopic large-scale shell-model calculations, and are discussed in terms of underlying shapes, as well as the role of neutron excitations across the $N=40$ gap. Enhanced axial shape asymmetry (triaxiality) is suggested to characterize $^{74}$Zn in its ground state. Furthermore, an excited $K=0$ band with a significantly larger softness in its shape is identified. A shore of the $N=40$ ``island of inversion'' appears to manifest above $Z=26$, previously thought as its northern limit in the chart of the nuclides.