absolute activity measurement of 125i seed brachytherapy by two-dimensional photon-photon coincidence spectroscopy

Photon-photon coincidence counting is a primary standardization technique used for the absolute activity measurement of short half-life radionuclides. in this study, a coincidence spectrometer based on digital signal processing was developed for the absolute standardization of 125i seed brachytherapy. the spectrometer includes a waveform digitizer that samples at the preamplifier signals directly from two similar 2ʺ × 2ʺ nai (tl) detectors. the sampled signals were shaped into trapezoidal signals for pulse height analysis. these detected signals were then recorded in a list file and the software was used to recognize coincidence events. detailed discussions were included on the formulas for determining absolute activity measurement. the activity of a 125i seed was measured and showed good agreement with the reference values. this presented technique is a quick method for measuring the activity of 125i at nuclear hospitals. the standardized source can also serve as a tracer for measuring the activity of the 109cd source.