Reinvestigation of low-lying levels of²³¹Th

Abstract

Low-lying excited levels of²³¹Th fed through α-decay of²³⁵U were investigated by using α-γ and γ-γ coincidence technique. From the analyses for co-relating energy levels and transition intensities, we found that the most favorable transition from 205.3 keV ([631]7/2) level that is fed by the most dominant α transition from²³⁵U is 19.6 keV transition (205.3 keV [631]7/2⁻→185.7 keV [631]5/2⁻). We also found that the transition probability of 109.2 keV, 205.3 keV [631]7/2⁻→96.1 keV [633]9/2⁺, was corrected to be weak. These findings can explain why the 185.7 keV γ-ray is so strongly observed, 0.57 photons/ga, in the γ-spectrum associated with the α-decay of²³⁵U. The decay scheme of²³¹Th levels previously reported has been modified according to the present analysis.