Constraining the ground-state spin of ⁷¹Kr by β-delayed proton emission

Nuclei in the vicinity of the N=Z line are a sensitive probe of isospin symmetry. In particular, the character of low-lying and ground states of the T=1/2 mirror pair, ⁷¹Kr and ⁷¹Br, has been under debate for several decades where ⁷¹Br has a first-excited state energy of only 10 keV. β-delayed protons emitted from ⁷¹Kr were measured via an implantation-decay experiment at NSCL using the Beta counting station coupled to SeGA. We report results on the first experimental observation of β-decay feeding the 407-keV level in ⁷¹Br and delayed-proton feeding to the 944-keV state of ⁷⁰Se. Several methods for determining the β-delayed proton branching were investigated, highlighting an often-neglected source of systematic error. The intensity of γ-ray transitions was used to build the low lying β-decay scheme of ⁷¹Kr, allowing for a better understanding of the symmetry between ⁷¹Kr and ⁷¹Br. This material is based upon work supported by the U.S. DOE, Office of Science, Office of Nuclear Physics under Award No. DE- FG02-94ER40848, DE-FG02-88ER40387 and DE-AC02-06CH11357; the NNSA through the Nuclear Science and Security Consortium under Award No. DE-NA0003180, DE-NA0003221, DE-NA0002132 and DE- NA0000979; and the NSF under Contract No. PHY-1102511.