Evaluation of Accuracy of Accumulated Dose of OB85 Gamma Irradiator

The purpose of this experiment was to evaluate the accuracy of accumulated doses used in irradiation and determination of transition timer error of sources in the OB85 Gamma Irradiator installed in Secondary Standard Dosimetry Laboratory at Atomic Energy Authority, Sri Lanka. Accumulated dose is measured using calibrated reference electrometer system (Electrometer: PTW, Model No: UNIDOS, S/No: 20567 and Ion chamber: 600cc, Model No: 2575C, S/No: 459) and compared with the calculated accumulated dose (= ref. dose rate x time) using reference dose rate and respective value of the timer of OB85. The experiment shows that, the transient time of the OB85 gamma irradiator is 1sec. The result concludes that minimum distance for accumulated dose below 1 mSv should be irradiated at 3m distance and 1mSv or above accumulated radiation doses should be irradiated at 1m distance in order to achieve accuracy at least 1%.