New isomeric transition in \(^{36}\)Mg: Bridging the N=20 and N=28 islands of inversion

• Published in: arXiv.org 2024-06
• Main Authors: Madurga, M, Christie, J M, Z Xu, Grzywacz, R, Poves, A, King, T, Allmond, J M, Chester, A, Cox, I, Farr, J, Fletcher, I, Heideman, J, Hoskins, D, Laminack, A, Liddick, S, Neupane, S, Richard, A L, Shimizu, N, Shuai, P, Siegl, K, Utsuno, Y, Wagenknecht, P, Yokoyama, R
• Format: Article
• Language: English
• Subjects: Configurations; Excitation; Intrusion; Islands; Nuclei
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2301.12002

We observed a new isomeric gamma transition at 168 keV in \(^{36}\)Mg, with a half-life of T\(_{1/2}\)=[130-500]\((\pm40)(^{+800}_{-20})_{sys}\) ns. We propose that the observed transition de-excites a new 0\(^+\) isomeric state and populates the previously known first 2\(^+\) state. The existence of this isomer is consistent with the predictions of the large-scale shell model calculations of \(^{36}\)Mg using the sdpf-u-mix interaction. The observed excitation energy of the second 0\(^+\) state is caused by the small energy separation between two prolate-deformed configurations where the intruder configuration corresponds to two neutron excitations from the {\it sd} to the {\it pf} shell. Within this interpretation, \(^{36}\)Mg becomes the crossing point between nuclei in which ground state deformed/superdeformed configurations are caused by the dominance of N=20 intruders (\(^{32,34}\)Mg) and nuclei where deformed configurations are associated with N=28 intruders (\(^{38}\)Mg and beyond). We found the lack of three-body monopole corrections in other effective interactions results in a predominance of N=20 intruder configurations past \(^{38}\)Mg incompatible with our observation. We conclude that \(^{36}\)Mg bridges the N=20 and N=28 islands of inversion, forming the so-called Big Island of Deformation.