Probing single-particle structures beyond the proton drip line

Abstract : Single-particle energies have been investigated in the closed neutron shell proton emitter ^{155}Ta. The ^{155}Ta nuclei were populated through the $\alpha$ decay of ^{159}Re, which has been observed for the first time. The ^{159}Re nuclei were produced in reactions of 300 MeV ^{58}Ni ions with an isotopically enriched ^{106}Cd target, separated in-flight using the RITU separator and implanted into the GREAT spectrometer. The ^{159}Re $\alpha$ decay emanates from the proton-emitting $\pi h_{11/2}$ state and populates a state in ^{155}Ta which decays by the emission of a proton from a $\pi h_{11/2}$ orbital. The results fit in with the systematics of proton and $\alpha$-particle separation energies in the region, but disagree with the previously reported decay properties of ^{155}Ta.