Determining the specific alpha activity of thick sources using a large-area zinc sulfide detector

A simple method using a large-area zinc sulfide detector to determine the total specific alpha activity of thick sources is presented. A previous paper shows how the linear absorption properties of weightless alpha sources can be applied to thick sources placed in direct contact with a varying thickness of window material. A quadratic relationship between the detector response and absorber thickness was derived for sources whose thickness exceeds the range of the alpha particle. The coefficient of the linear term in the quadratic expression is used to calculate the total specific alpha activity of a source in contact with the window of the detector. This relationship is tested by obtaining alpha absorption data from solid sources of known specific alpha activity, fitting the data to the theoretical relationship and comparing the results to the known activities.