Discovery of Rb 72: A Nuclear Sandbank beyond the Proton Drip Line

H. Suzuki, L. Sinclair, P. A. Söderström, G. Lorusso, P. Davies, L. S. Ferreira, E. Maglione, R. Wadsworth, J. Wu, Z. Y. Xu, S. Nishimura, P. Doornenbal, D. S. Ahn, F. Browne, N. Fukuda, N. Inabe, T. Kubo, D. Lubos, Z. Patel, S. RiceY. Shimizu, H. Takeda, H. Baba, A. Estrade, Y. Fang, J. Henderson, T. Isobe, D. Jenkins, S. Kubono, Z. Li, I. Nishizuka, H. Sakurai, P. Schury, T. Sumikama, H. Watanabe, V. Werner

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20 Scopus citations


In this Letter, the observation of two previously unknown isotopes is presented for the first time: Rb72 with 14 observed events and Zr77 with one observed event. From the nonobservation of the less proton-rich nucleus Rb73, we derive an upper limit for the ground-state half-life of 81 ns, consistent with the previous upper limit of 30 ns. For Rb72, we have measured a half-life of 103(22) ns. This observation of a relatively long-lived odd-odd nucleus, Rb72, with a less exotic odd-even neighbor, Rb73, being unbound shows the diffuseness of the proton drip line and the possibility of sandbanks to exist beyond it. The Rb72 half-life is consistent with a 5+→5/2- proton decay with an energy of 800-900 keV, in agreement with the atomic mass evaluation proton-separation energy as well as results from the finite-range droplet model and shell model calculations using the GXPF1A interaction. However, we cannot explicitly exclude the possibility of a proton transition between 9+(Rb72)→9/2+(Kr71) isomeric states with a broken mirror symmetry. These results imply that Kr72 is a strong waiting point in x-ray burst rp-process scenarios.

Original languageEnglish
Article number192503
JournalPhysical Review Letters
Issue number19
StatePublished - Nov 6 2017


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