Measurement of Effective Neutron Capture Cross Section of 166mHo using Two Step Irradiation Technique

Holmium-166m is one of the long-lived fission products, whose half-life is 1,200 yrCll. In the course of the systematic studyC2 ) of neutron capture cross sections of fission products, the thermal neutron capture cross section of 166mHo has been measured. There is no experimental data of thermal neutron capture cross section for 166mHo, except the resonance parameter measured by Masyanov et al.C3 l. They identified three resonances of 166mHo in the energy range of 0.001137 eV, and calculated from the resonance parameters the thermal capture cross section of 166mHo as 9.1±0. 7 kb and the resonance integral as 1.1±0.1 kb. They assumed the statistical weight of the channel spin C 4), g, be equal to 1. Present note describes the measurement of the effective capture cross section for thermal neutron of 166mHo by an activation method that is free from the ambiguity of the g factor. Two-step irradiation technique is introduced to make an activation method effective. The obtained value of the cross section, 3±1 kb, is about three times smaller than the value reported in Ref. (3).