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

The β -delayed γ 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 ^81mGe^+ 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.