Spectral and angular characteristics of the radiation from a cylindrical radionuclide source

In measuring the activity of volume of radionuclide sources, it is necessary to know how the number of particles N incident on the detector in unit time depends on the activity A of the source. In the general case, the coefficient χ in the relationship N=χA depends in a complex manner on the type of radiation, relative positioning of source and detector, self-absorption in the source and absorption in the medium, the shape of the source, the presence of reflection, and many other factors. A method is proposed in the present paper for calculating the yield of γ and β radiation from volume gas-filled radionuclide sources. Specifically, the source considered takes the form of a cylindrical vessel filled with air and a small addition of radioactive krypton-85. The detector with a small circular entrance diaphragm is situated at one end of the cylinder. The 85Kr concentration and also the total source activity are initially unknown, and their determination is the main purpose of the present work. Since for β-decay of the 85Kr nucleus, γ rays (of energy 514 keV) are given off together with β particles, the source activity can be found in two ways, from the γ or β radiation. It is a purely geometric problem to find the relationship between source activity and detector count rate. 9 refs., 5 figs