In-beam γ-ray spectroscopy of the proton emitter69147Tmusing recoil-decay tagging

Abstract

Gamma rays from the decay of states in the proton unstable nucleus ${}^{147}$Tm were observed for the first time following the ${}^{92}$Mo${(}^{58}$Ni,p2n)${}^{147}$Tm reaction at 260 MeV. Prompt $\ensuremath{\gamma}$ rays were detected with an array of Compton-suppressed Ge detectors, placed in front of the fragment mass analyzer at the ATLAS accelerator, and were assigned to individual reaction channels on an event-by-event basis using the recoil-decay tagging method. Gamma-ray transitions were associated with both the proton decay of the $\ensuremath{\pi}$${h}_{11/2}$ ground state and the $\ensuremath{\pi}$${d}_{3/2}$ isomeric state in ${}^{147}$Tm, even though the cross sections for populating these states were only $\ensuremath{\approx}$ 16 $\ensuremath{\mu}$b and 2 $\ensuremath{\mu}$b, respectively. The level scheme which was constructed for ${}^{147}$Tm is discussed and compared with the level structures for lighter $N$=78 isotones.