β decay of the $T=0\mathrm{}$ isomer in the $N=Z$ proton drip-line nucleus ${}^{70}\mathrm{Br}$

We have investigated the β decay of the $T=0,$ $T_{1/2}\approx 2.2\mathrm{s},$ isomeric level in the self-conjugate odd-odd nucleus ${}^{70}\mathrm{Br}.$ The observed β-delayed γ rays in the daughter nucleus ${}^{70}\mathrm{Se}$ and the deduced decay properties of the isomeric level allow, in conjunction with results from the deformed shell model, a spin and parity assignment of $J^{\pi }{=9\mathrm{}}^{+}$ and suggest a structure of $\{\pi \left[404\right]{9/2}^{+}\nu \left[404\right]{9/2}^{+}\}{9}^{+}.$ The allowed unhindered β decay of the isomer, possibly oblate deformed, proceeds to four-quasiparticle states in ${}^{70}\mathrm{Se}.$