Improved Value for the Gamow-Teller Strength of the Sn100 Beta Decay

Abstract

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

Mass measurements of 99–101In challenge ab initio nuclear theory of the nuclide 100Sn

“…However, combining our result with the more recently published β-decay Q-value (that is, the energy released in the decay) from ref. 5 yields a 100 Sn mass excess of −56,488(160) keV. For both decay energies, the 100 Sn mass is found to be more bound than previously inferred.…”

“…The experimental results are compared with ab initio many-body calculations. The 100-fold improvement in precision of the 100 In mass value highlights a discrepancy in the atomic-mass values of 100 Sn deduced from recent beta-decay results 4,5 . The nuclear landscape is shaped by the underlying strong, weak and electromagnetic forces.…”

“…between the Q-values from refs. 4,5 yields 100 Sn mass values that differ by 650 keV. We examine the consequences below and resolve this inconsistency.…”

“…Eliminating the contribution of the 100 In ground-state mass uncertainty in the calculation of the 100 Sn mass directly allows to confront the nuclear-structure implications of the two Q-values from refs. 4,5 , and a global picture now emerges for this region. As shown, the Q-value reported by Lubos et al 5 yields a 100 Sn mass value that is at odds with the expected trend of Δ 2n (Z, N 0 + 2) to Z = 49 (open blue circle in the bottom panel of Fig.…”

“…Nuclei in the immediate vicinity of 100 Sn offer important insight for understanding the single-neutron and proton states in this region and constitute an excellent proxy for the study of 100 Sn itself. However, experiments have so far only been feasible with in-beam gamma-ray spectroscopy at fragmentation facilities 4,5,[7][8][9][10] . By direct determination of the nuclear binding energy, high-precision atomic-mass measurements provide a crucial model-independent probe of the structural evolution of exotic nuclei.…”