Decay of the very neutron-deficient isotope $^{131}$Pm

The decay of 131Pm has been investigated by means of γ-ray spectroscopy. The 131Pm nuclei were produced by fusion-evaporation reaction of 106Cd(32S,3p4n) at the beam energy of 170 MeV. A helium-jet technique and a tape transport system were used to collect the activities and transfer them to a detecting position for X and γ rays measurement. Two γ rays of 185.0 and 220.0 keV were unambiguously identified to follow the β+ decay of 131Pm by results of X-γ and γ–γ coincidence. A growth-decay feature of the decay curve for 87.8 keV γ-ray of 131Nd confirmed the production of 131Pm nuclei. The half-life of 131Pm was measured to be 6.3 ± 0.8 s. A partial decay scheme of 131Pm is proposed on the basis of X-γ and γ–γ coincidence data in this experiment and the known structure information deduced from in-beam experiments of the daughter nucleus 131Nd.