Simultaneous investigation of the T=1(Jπ=0+) and T=0(Jπ=9+) β decays in Br70
AbstractThe β decay of the odd-odd nucleus Br70 has been investigated with the BigRIPS and EURICA setups at the Radioactive Ion Beam Factory (RIBF) of the RIKEN Nishina Center. The T=0(Jπ=9+) and T=1(Jπ=0+) isomers have both been produced in in-flight fragmentation of Kr78 with ratios of 41.6(8)% and 58.4(8)%, respectively. A half-life of t1/2=2157−49+53 ms has been measured for the Jπ=9+ isomer from γ-ray time decay analysis. Based on this result, we provide a new value of the half-life for the Jπ=0+ ground state of Br70,t1/2=78.42±0.51 ms, which is slightly more precise, and in excellent agreement, with the best measurement reported hitherto in the literature. For this decay, we provide the first estimate of the total branching fraction decaying through the 21+ state in the daughter nucleus Se70,R(21+)=1.3±1.1%. We also report four new low-intensity γ-ray transitions at 661, 1103, 1561, and 1749 keV following the β decay of the Jπ=9+ isomer. Based on their coincidence relationships, we tentatively propose two new excited states at 3945 and 4752 keV in Se70 with most probable spins and parities of Jπ=(6+) and (8+), respectively. The observed structure is interpreted with the help of shell-model calculations, which predict a complex interplay between oblate and prolate configurations at low excitation energies.