Experimental re-evaluation of the gamma-ray energy and emission probability for the 159 keV transition in 238U following the alpha-decay of 242Pu.

摘要

Because of the very low specific activity of (242)Pu, the non-destructive assay of this isotope by means of conventional high-resolution gamma-spectrometry (HRGS) is possible only for Pu samples highly rich in (242)Pu. For bulk samples suffering from the gamma self-attenuation and self-fluorescence effects, the only practical choice for the quantitative analysis of (242)Pu is the weak gamma-line emitted in the 159 keV transition of its alpha-decay daughter (238)U. A recent study revealed a significant disagreement between the (242)Pu mass values in a 99.72% enriched (242)PuO(2) sample as reported by HRGS and neutron coincidence counting. This fact motivated the present study on the experimental re-evaluation of the gamma-emission probability for the 159 keV transition using a combination of alpha-, gamma- and mass-spectrometry techniques. The obtained new emission probability P(2)=(2.20+/-0.08)10(-6) turned out to be approximately 35% smaller than the currently adopted value. The study also suggested a new value E(2)=159.018+/-0.016 keV for the energy of the respective gamma-ray.