Formation Cross Sections of Zirconium-90m and Lead-207m with Fast Neutrons

Abstract

Abstract The cross sections for the formation of the metastable states of 90Zr, (σ zr), for neutron energy of 14.8 MeV, and that of 207Pb, (σ pb,), for neutron energies from 4.1 to 5.2 MeV have been measured and the results are reported. The experimentally determined value of the cross section for the former is 700±94mb, while for the latter, the cross section increases from 316 + 44 mb to 788±110 mb. The cross section ratio, σpb/σZr, is also studied, which is found to vary from 1.87 to 2.18 for neutron energies from 14.8 to 18.2 MeV respectively. The equality in the half-lives of the metastable states of 90Zr and 207Pb is exploited in the present measurements, which enabled comparative evaluation of the cross sections. Natural samples of zirconium and lead were irradiated simultaneously and the x-rays were measured off-line by a 55 cm3 Ge(Li) detector. Cyclic activation process was adopted to improve the counting statistics. The overall accuracy achieved in the measurements is about 10%.