Standardization of 125I and 109Cd by the photon–photon coincidence method in PTKMR-BATAN

A photon–photon coincidence system was constructed for the standardization of 125I and 109Cd in PTKMR-BATAN, Indonesia. Two NaI(Tl) detectors of 76 mm diameter × 6 mm thickness with 0.5 mm aluminum window were used, which were positioned approximately symmetrically to the source holder. The electronic chain was almost the same as for a 4πβ-γ system. The CANBERRA Multiport II multi channel analyzer was used for energy calibration and a Philips type PM3092 oscilloscope for visualization of the pulses. A polyethylene plastic was used as the source substrate for the 125I and 109Cd samples. The activity of a 125I solution was measured by the photon–photon coincidence and the efficiency extrapolation method (), whereas the activity of a 109Cd solution was determined by a tracer method using 125I (). The result of the 125I activity showed good agreement with the result of measurements using a calibrated ionization chamber, and the result of 109Cd also showed good agreement with the measurements result using a LEGe detector. - Highlights: ► The activity of a 125I and109Cd solution was measured by the photon–photon coincidence. ► Samples were prepared into solid point source, dropped onto a thin polyethylene plastic. ► The photon are counted using two movable NaI(Tl) detectors. ► The result of activity showed good agreement with the result of measurements using a calibrated IC and an LE(Ge) detector.