β decay of the very neutron-deficient Ge60 and Ge62 nuclei

Abstract

We report here the results of a study of the β decay of the proton-rich Ge isotopes, 60 Ge and 62 Ge, produced in an experiment at the RIKEN Nishina Center. We have improved our knowledge of the half-lives of 62 Ge [73.5(1) ms] and 60 Ge [25.0(3) ms] and its daughter nucleus, 60 Ga [69.4(2) ms]. We measured individual βdelayed proton and γ emissions and their related branching ratios. Decay schemes and absolute Fermi and Gamow-Teller transition strengths have been determined. The mass excesses of the nuclei under study have been deduced. A total β-delayed proton-emission branching ratio of 67(3)% has been obtained for 60 Ge. New information has been obtained on the energy levels populated in 60 Ga and on the 1/2 − excited state in the β p daughter 59 Zn. We extracted a ground state-to-ground state feeding of 85.3(3)% for the decay of 62 Ge. Eight new γ lines have been added to the deexcitation of levels populated in the 62 Ga daughter.

Mass measurements of Ga60–63 reduce x-ray burst model uncertainties and extend the evaluated T=1 isobaric multiplet mass equation

“…Since our direct mass measurement is essentially free from additional assumptions, our 60 Ga mass value can be considered more reliable than previous results. Our mass excess value of −40005 (30) keV lies more than 400 keV below the AME2020 [26] value of −39590 # (200 # ) keV extrapolated from trends in the mass surface ( # ), but is consistent with the [26], the semiempirical estimate from Mazzocchi et al [69] and the indirect experimental result from Orrigo et al [70]. The last column indicates the deviations between our mass excess values and the ones from AME2020.…”

“…AME2003 [86] value of −40000 # (110 # ) keV. In this region of the nuclear chart, multiple other works [70,[87][88][89] have found similar discrepancies with extrapolated values from atomic mass evaluations after AME2003. Our measured 60 Ga mass adds an important anchor point to mitigate these issues in future mass evaluations.…”

“…Their underlying hypothesis about the gamma de-excitation of the IAS is strengthened by mirror symmetry arguments. However, they conceded that the discrepancy between the observed Fermi transition strength (B(F ) = 3.1(1)) and theoretical expectation (B(F ) = 4) could be caused by undetected gamma transitions [70] from the IAS. This raises questions about the reliability of the mass excess deduced in that study.…”

“…This study experimentally established the half-life of 60 Ga and identified the isobaric analog state (IAS) in 60 Zn. Based on the well-known mass of the IAS in 60 Zn and systematics of experimental CDEs [85], they deduced a semi-empirical estimate for the 60 Ga mass excess of −40010 (60) keV and a corresponding one-proton separation energy of 40 (70) keV.…”

“…A recent study of the β-decay of 60 Ge by Orrigo et al [70] determined the mass excess of the IAS in 60 Ga and provided a more precise derivation of the 60 Ga groundstate mass. In that experiment, the 60 Ge decays populated excited states in the daughter nuclide 60 Ga, which then either de-excited via gamma emission or decayed to states in 59 Zn by emission of a proton (β-delayed proton emission).…”