Development of 'powder sandwich' technique for determining thoron emanation coefficient for thorium bearing powders

This study presents a new method that has been developed for the correct estimation of thoron emanation coefficient from powders or sands with considerably high 224Ra content. The technique utilizes a closed loop setup in which thoron emitted from a thin layer of sample in the 'powder sandwich' (PS) is measured using suitable thoron detector and the mass exhalation rate is determined. The powder sandwich is prepared by carefully placing a known mass (M) of source powder, about 100 mg, between two glass fiber filter papers. This arrangement is sealed at edges using adhesive, to avoid any spillage or loss of the powder. The powder sandwich arrangement ensures that the thickness of thoron sample is much less than the thoron diffusion length, allowing all the thoron gas produced to come out through the filter paper. The powder sandwich made as above is then placed in a closed loop containing a thoron detector and a pump. When the pump is turned on, it circulates the air in the closed loop causing all the thoron gas formed in the powder sandwich to come out. Within few minutes, the thoron concentration in the closed loop reaches an equilibrium value. This thoron concentration is measured using a thoron detector