Simultaneous measurement of radon and thoron using Lucas scintillation cell

A method has been developed for the simultaneous measurement of radon (Rn222) and thoron (Rn220) in a mixed environment using the Lucas scintillation cell (LSC). The method uses counts from two arbitrary counting intervals from zero time with respect to sampling hence, called two count method (TCM). The basis of the method involves formulation of simultaneous linear equations with two unknown variables. The unknown variables represent the radon and thoron activities in the cell. The coefficients of the equations are the integrated activities of radon, thoron and their alpha decay products per unit activities of the parent radionuclides. The method can be used to estimate the radon and thoron concentrations in a mixed environment accurately and quickly, as there is no need to delay the counting to achieve complete decay of thoron. The mathematical basis of the method along with few experimental results is presented in this paper. Results yielded, on comparison, good agreement with the delay count method (DCM) and double filter measurement (DFM) technique. Multiple regression analysis is also carried out to get the concentrations of radon and thoron from the counts obtained for various counting intervals. The corresponding growth factors of radon and thoron also showed good comparison with the average concentrations obtained from the two count approach for different counting intervals. Use of LSC for routine environmental measurements has its limitation due to high minimum detection level (MDL) values. However, LSC is commonly used in uranium mines, high background radiation areas and in calibration experiments. The present methodology is a very convenient approach to measure radon and thoron simultaneously especially in calibration experiments.