Experimental beta-decay energies of 91,92Br

Abstract

Abstract At the mass separator ISOLDE II, the β-decay energies of the neutron-rich Br isotopes with mass number A = 91 and A = 92 have been measured. With a large Ge(hp) detector and a ΔE – E plastic scintillator telescope, βγ-coincidences as well as β-singles and γ-singles spectra were recorded. From the βγ-matrices, 14 and 15 independent β-spectra in coincidence with different γ-transitions were evaluated for the two isotopes respectively. The final Oβ values are: 9790 ± 100 keV for 91 Br and 12155 ± 100 keV for 92Br. In addition. Qβ values could also be derived from the same βγ-coincidence matrices for the daughter nuclei 91Kr and 92Kr. The values obtained agree well with those given in the literature. In a plot of the one-neutron separation energies of the nuclei in this mass region, the subshell closure effect at N = 56 is also observed for the Br isotopes with Z = 35, contrary to theoretical predictions. Finally, the mass excesses for 91,92Br and 91,92Kr are calculated and compared with recent predictions of different mass formulae.