Assessment of heavy radioactive elements in sodium iodide scintillators

Two methods have been used to measure alpha particle emitters in a large thallium activated sodium iodide scintillator. By combining the results from delayed coincidence measurements and those from pulse shape discrimination it was possible to identify the isotopes responsible for the various peaks in the alpha particle spectrum. It was also possible to determined whether the thorium and uranium series were in secular equilibrium. The total rate of alpha particles was 26 ± 1 kg−1 d−1.