Radioactivity of thorium and feasibility of in vivo thorium measurements.

Tabulations of the radioactivity in the thorium series decay chain and a discussion of the radioactivity variations possible in non-equllibrium conditions of the decay chain are presented. Experimental data indicate that the daughters of thorium within the human lung may be measured by in vivo gamma spectrometry and related to Th/sup 232/ content for thorium quantities as small as 9 mug, if the activity ratio of Th/sup 232/: Th/sup 228/ is knowu for the deposited material. Two crystel gamma coincidence measurements of pairs of the simultaneously emitted gamma quanta from the daughters are suggested as a promising approach to thorium in vivo measurements. (auth)