Using fusion-evaporation reactions, a gas-filled recoil separator, recoil-gating technique and recoil-isomer decay tagging technique we have extended the level scheme of ${}^{203}\mathrm{At}(N=118)$ significantly. We have observed an isomeric $[\tau =14.1(3\left)\mu \mathrm{s}\right]$ state with a spin and parity of $29/2^{+}$. The isomeric state is suggested to originate from the $\pi \left(h_{9/2}\right)\otimes |{}^{202}\mathrm{Po};{11}^{-}\rangle$ coupling, and it is depopulated through 286 keV $E2$ and 366 keV $E3$ transitions. In addition, we have observed a cascade of magnetic-dipole transitions which is suggested to be generated by the shears mechanism.

• Received 22 December 2017

DOI:https://doi.org/10.1103/PhysRevC.97.024301