No abstract

Excited states in the N ¼ 102 isotones 166 Gd and 164 Sm have been observed following isomeric decay for the first time at RIBF, RIKEN. The half-lives of the isomeric states have been measured to be 950(60) and 600(140) ns for 166 Gd and 164 Sm, respectively. Based on the decay patterns and potential energy surface calculations, including β 6 deformation, a spin and parity of 6 − has been assigned to the isomeric states in both nuclei. Collective observables are discussed in light of the systematics of the region, giving insight into nuclear shape evolution. The decrease in the ground-band energies of 166 Gd and 164 Sm (N ¼ 102) compared to 164 Gd and 162 Sm (N ¼ 100), respectively, presents evidence for the predicted deformed shell closure at N ¼ 100. In the exploration of the nuclear landscape, it is evident that the neutron-rich side of stability contains a vast unknown territory, where approximately half of all the bound nuclides remain to be identified. Furthermore, this is the domain of rapid-neutron-capture (r process) nucleosynthesis, which is poorly understood and yet is key to the creation of chemical elements from iron to uranium (Z ¼ 26-92) in stellar environments [1]. With the advent of the current generation of radioactive-beam facilities, it is now possible to address some of the open questions PRL 113, 262502 (2014) P H Y S I C A L

A record number of 100 Sn nuclei was detected and new isotopic species toward the proton dripline were discovered at the RIKEN Nishina Center. Decay spectroscopy was performed with the high-efficiency detector arrays WAS3ABi and EURICA. Both the half-life and the β-decay end point energy of 100 Sn were measured more precisely than the literature values. The value and the uncertainty of the resulting strength for the pure 0 þ → 1 þ Gamow-Teller decay was improved to B GT ¼ 4.4 þ0.9 −0.7 . A discrimination between different model calculations was possible for the first time, and the level scheme of 100 In is investigated further.Sn and its neighboring nuclei comprise a unique testing ground for modern large scale shell model (LSSM) calculations with realistic nuclear interactions. 100 Sn is the heaviest doubly magic N ¼ Z nucleus that is particle stable and decays via a pure and very fast Gamow-Teller (GT) β decay. The 100 Sn region is located in the nuclear chart close to the end of the astrophysical rapid proton capture process path. Thus, it is of particular interest concerning fundamental challenges in both nuclear physics and astrophysics [1].According to the extreme single particle model (ESPM) [2], 100 Sn decays via a pure GT transition of a proton (π) from the completely filled π0g 9=2 orbital into a neutron (ν) in the empty spin-orbit partner, the ν0g 7=2 orbital of 100 In. The ESPM GT strength is predicted to be B GT ¼ 17.78 [1]. However, the experimental values obtained up to now are smaller: 9.1 þ3.0 −2.6 [3] and 5.8 þ5.5 −3.2 [4,5]. These experiments [3,5,6] revealed the smallest log(ft) value-even smaller than the values of nuclei which decay by a Superallowed Fermi decay-throughout the nuclear chart. However, the PHYSICAL REVIEW LETTERS 122, 222502 (2019) 0031-9007=19=122 (22)=222502(6) 222502-1

No abstract

No abstract