Observation of the exotic nucleus145Tmvia its direct proton decay

Proton emission from ${}^{145}\mathrm{Tm}$ was observed for the first time via the ${}^{92}\mathrm{Mo}{(}^{58}\mathrm{Ni},p4n)$ reaction, using the Holifield Radioactive Ion Beam Facility Recoil Mass Spectrometer in conjunction with a double-sided Si strip detector at the focal plane. The measured energy of the emitted proton is 1.728(10) MeV and its half-life is 3.5(10) μs, the shortest ever observed for ground-state proton radioactivity. When compared to the calculated WKB half-life for an $l=5\mathrm{}$ transfer, the spectroscopic factor is 0.51(16), which is consistent with the value of 0.64 calculated via the BCS approximation for a spherical nucleus. Also, the half-life of ${}^{113}\mathrm{Cs}$ was determined with a greater precision than previously available to be 16.7(7) μsec.