First trap-assisted decay spectroscopy of the ${}^{81}$Ge ground state

The $\beta$-delayed $\gamma$ spectroscopy of ${}^{81}$As has been performed using a purified beam of ${}^{81}$Ge (9/2${}^{+}$) ground state at the Ion Guide Isotope Separator On-Line facility (IGISOL). The ${}^{81}$Ge${}^{+}$ ions were produced using proton-induced fission of ${}^{232}$Th and selected with the double Penning trap JYFLTRAP for the post-trap decay spectroscopy measurements. The low-spin (1/2${}^{+}$) isomeric-state ions ${}^{81m}$Ge${}^{+}$ were not observed in the fission products. The intrinsic half-life of the ${}^{81}$Ge ground state has been determined as T${}_{1/2}$ = 6.4(2) s, which is significantly shorter than the literature value. A new level scheme of ${}^{81}$As has been built and is compared to shell-model calculations.