On the determination of activity profiles in wide-area reference sources

A method is described for determining the depth distribution of the radioactive substance of alpha-emitting nuclides in a wide-area reference source. The method combines measurements and calculations. In the experimental part, the energy spectrum of the source is measured by means of an alpha spectrometer. The energy spectrum is then modelled by the Monte Carlo method, taking into account energy loss of alpha particles in the source matrix, energy-loss straggling and the parameters of the spectrometer. Additional parameters for the characterization of reference sources are derived from the integral of the depth distribution. The investigations prove that the production process of commercial sources can be controlled in such a way that more than 90% of the radioactive material is implanted in the top layer of 5 microm thickness of an aluminum foil.