ePhysics

Gamma-gamma coincidence detection was first used by Eldridge for the purpose of measuring the activity of ¹²⁵I. Involving two detectors and a radioactive source which emits two or more gamma rays simultaneously, one can infer the activity of the source by examining both coincident and non-coincident counts of gamma rays on the detectors. Although this method has previously been used for sources which emit low-energy gamma rays, where the effect of Compton scattering is negligible, the purpose of this project was to demonstrate that it can be implemented for sources with high-energy gamma rays. While ⁶⁰Co was the primary focus of this project, we also considered ²²Na and ^108mAg.

A significant advantage of gamma-gamma coincidence detection is that it does not depend on the geometric configuration of the experiment. In order to verify this, we applied this method to data collected for radioactive sources placed at equal distances from the two detectors, or closer to one detector than another. In both cases, the same value for the activity was produced with small differences (less than 0.5%), while our results coincided with measurements made using beta-gamma coincidence detection.

Absolute ⁶⁰Co characterization based on gamma–gamma coincident detection by two NaI(Tl) detectors: P. Volkovitsky and P. Naudus, Nucl. Instr. and Meth. 607, 568 (2009)