Calibration of γ-ray sources without standards

A simple method of estimating the activity of cylindrical γ-ray sources without the use of standards is developed. The method is based on evaluating the total detection efficiency and measuring the corresponding photofraction. The method is employed to calibrate cylindrical sources of various energies. Comparison between the present method and the conventional methods employing standard sources is satisfactory and yielding differences that do not exceed 5%. Values of the total detection efficiency for three commonly used sizes of NaI(Tl) cylindrical well detectors are presented. (author)