Identification of a proton-emitting isomer in 151Lu

An isomer of Lu-151 was identified by its direct proton radioactivity. It was produced by bombardment of Ru-96 With 266-MeV Ni-58 from the Holifield Radioactive-Ion Beam Facility, mass separated with a recoil separator and implanted in a double-sided silicon strip detector, which provided signals to correlate each proton decay with a particular implant. The proton energy and half-life of Lu-151(m) were measured to be 1310(10) keV and 16(1) mu s, respectively. The half-life of the previously known hll, ground state was observed to be 80(2) ms in agreement with the previously adopted value of 88(10) ms. Comparison of the half-life of Lu-151(m) with WKB barrier-penetration calculations leads to the conclusion that the isomer is a d(3/2) proton state. A two-potential approach predicts a half-life of 5.5(-1.1)(+1.4) mu s which yields an experimental spectroscopic factor of 0.34(-0.08)(+0.12).