APS : First Evidence of Axial Shape Asymmetry and Configuration Coexistence in Zn74: Suggestion for a Northern Extension of the N=40 Island of Inversion

Rocchini, M.; Natzke, C.; Ball, G.C.; Lubna, R.S.; Sharma, S.; Griffin, C.J.; Hackman, G.; Zidar, T.; Suh, J.; Radich, A.J.; Babu, A.; Bhattacharjee, S.S.; Pannu, S.; Laffoley, A.T.; Garrett, P.E.; Zielínska, M.; Nowacki, F.; Cheng, C.; Ahmed, Z.T.; MacLean, A.D.; Gillespie, S.; Coleman, R.; Paxman, C.; Andreoiu, C.; Shadrick, S.; Illana, A.; Rajabali, M.M.; Olaizola, B.; Hanley, M.; Lenzi, S.M.; Leach, K.G.; Svensson, C.E.; Garnsworthy, A.B.; Porzio, C.; Bidaman, H.; Sarazin, F.; Jones, S.; Dao, D.D.; Dillmann, I.; Grinyer, G.F.; McAfee, J.; Schwarz, K.; Bildstein, V.; Yates, D.

doi:10.1103/PhysRevLett.130.122502

Article
Report number	arXiv:2302.07394
Title	First Evidence of Axial Shape Asymmetry and Configuration Coexistence in ${}^{74}{Zn}$ : Suggestion for a Northern Extension of the $N = 40$ Island of Inversion
Author(s)	Rocchini, M. (Guelph U.) ; Garrett, P.E. (Guelph U.) ; Zielínska, M. (IRFU, Saclay) ; Lenzi, S.M. (Padua U. ; INFN, Padua) ; Dao, D.D. (Strasbourg, IPHC) ; Nowacki, F. (Strasbourg, IPHC) ; Bildstein, V. (Guelph U.) ; MacLean, A.D. (Guelph U.) ; Olaizola, B. (TRIUMF ; CERN) ; Ahmed, Z.T. (Guelph U.) ; Andreoiu, C. (Simon Fraser U.) ; Babu, A. (TRIUMF) ; Ball, G.C. (TRIUMF) ; Bhattacharjee, S.S. (TRIUMF) ; Bidaman, H. (Guelph U.) ; Cheng, C. (TRIUMF) ; Coleman, R. (Guelph U.) ; Dillmann, I. (TRIUMF ; Victoria U.) ; Garnsworthy, A.B. (TRIUMF) ; Gillespie, S. (TRIUMF) ; Griffin, C.J. (TRIUMF) ; Grinyer, G.F. (Regina U.) ; Hackman, G. (TRIUMF) ; Hanley, M. (Colorado School of Mines) ; Illana, A. (Jyvaskyla U.) ; Jones, S. (Tennessee U.) ; Laffoley, A.T. (Guelph U.) ; Leach, K.G. (Colorado School of Mines) ; Lubna, R.S. (TRIUMF) ; McAfee, J. (TRIUMF ; Surrey U.) ; Natzke, C. (TRIUMF ; Colorado School of Mines) ; Pannu, S. (Guelph U.) ; Paxman, C. (TRIUMF ; Surrey U.) ; Porzio, C. (TRIUMF ; INFN, Milan ; Milan U.) ; Radich, A.J. (Guelph U.) ; Rajabali, M.M. (Tennessee Tech. U.) ; Sarazin, F. (Colorado School of Mines) ; Schwarz, K. (TRIUMF) ; Shadrick, S. (Colorado School of Mines) ; Sharma, S. (Regina U.) ; Suh, J. (Regina U.) ; Svensson, C.E. (Guelph U.) ; Yates, D. (TRIUMF ; British Columbia U.) ; Zidar, T. (Guelph U.)
Publication	2023-03-24
Imprint	2023-02-14
Number of pages	6
In:	Phys. Rev. Lett. 130 (2023) 122502
DOI	10.1103/PhysRevLett.130.122502 (publication)
Subject category	nucl-th ; Nuclear Physics - Theory ; nucl-ex ; Nuclear Physics - Experiment
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.
Copyright/License	preprint: (License: arXiv nonexclusive-distrib 1.0) publication: © 2023-2024 American Physical Society

$Measured $\gamma$-$\gamma$ angular correlation functions $W(\theta)$, where $\theta$ is the opening angle between the GRIFFIN detectors, and reduced $\chi^2$ as a function of the arctangent of the mixing ratio $\delta$, for the $0_2^+ \to 2_1^+ \to 0_1^+$ (panels a and b) and $3_1^+ \to 2_1^+ \to 0_1^+$ cascades (panels c and d). The energies of the states involved in each cascade (in keV) are indicated. The $\chi^2$ distributions corresponding to different spin hypotheses for the initial state are labelled accordingly, with the continuous lines indicating the $99\%$ confidence limit.$ $Portions of the $^{74}$Zn $\gamma$-ray spectra in coincidence with $\gamma$ rays: (a) 812 keV ($4_1^+ \to 2_1^+$) (b) 1183 keV ($0_2^+ \to 2_1^+$). The 730-keV and 359-keV $\gamma$ rays are newly assigned as the $2_3^+ \to 4_1^+$ and $2_3^+ \to 0_2^+$ transitions, respectively. The 681-keV and 710-keV $\gamma$ rays were observed previously~\cite{tracy-2018}.$ $Partial experimental level scheme of $^{74}$Zn (EXP) compared with shell-model calculations (SM) and shell-model calculations in a deformed Hartree-Fock basis (DNO-SM). The states are labelled with their spin, parity, and energy (in keV) and organized in bands. Only in-band transitions are displayed, and their labels correspond to calculated $B(E2)$ values in W.u.$ Show more plots

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