Study on the calibration method of absorbed dose to water using pinpoint ionization chamber

Objective: To establish a calibration method of the absorbed dose to water using pinpoint ionization chamber at the radiation quality of ⁶⁰CO gamma rays. Methods: Reference dosimeter (FC65-G Farmer ionization chamber with DOSE 1 electrometer) was calibrated by the China Institute of Metrology for obtaining the absorbed dose calibration factor to water. ⁶⁰Co gamma rays and the IAEA TRS-398 measuring procedure were used to measure the absorbed dose at depth of 10 cm water with the reference dosimeter. Alternative method, the water absorbed dose measurement and calibration of two pinpoint ionization chamber dosimeters were carried out. Replacing the ⁶⁰Co gamma radiation field, the reference dosimeter and two pinpoint ionization chamber dosimeters were used to verify the dose. Results: The measured results of absorbed dose to water at depth of 10 cm water at reference conditions were 0.2499 Gy for reference dosimeter, 0.2480 Gy and 0.2500 Gy for two pinpoint ionization chambers, respectively. The relative deviations of the measurement were within ± 0.8% between the reference dosimeter and two pinpoint ionization chamber dosimeters. The measurement uncertainty of the pinpoint ionization chamber was 2.8% (k = 2). Conclusion: The pinpoint ionization chamber can be used to measure the absorbed dose to water of small field. (authors)