First decay study of the new isotope Pm-129 near the proton drip line

The very neutron-deficient nuclide Pm-129 was produced via the Mo-92(Ca-40, p2n) reaction and identified for the first time by using the X-gamma coincidence in combination with a He jet tape transport system. According to the decay curve of a 99 keV gamma-ray which corresponds to the known 5/2(-) --> 1/2(-) transition in the daughter nucleus Nd-129 of the Pm-129 decay, the half-life of Pm-129 was determined to be 2.4(9) s. Based on the nuclear potential energy surface (PES) calculations, the ground-state spin-parity of Pm-129 was predicted as 5/2(-) which is favorable to feed a 5/2(-) low-lying state in the daughter nucleus Nd-129 via the (EC + beta(+)) decay.