针尖电离室水中吸收剂量校准方法研究

目的 ⁶⁰Co γ射线下，建立针尖电离室水中吸收剂量校准方法。方法 参考剂量仪（DOSE 1静电计+FC65-G型电离室）经过中国计量科学研究院校准，得到水中吸收剂量校准因子。采用⁶⁰Co γ射线，IAEA TRS-398测量程序，用参考剂量仪测量水下10 cm吸收剂量。替代法，用针尖电离室剂量仪进行水吸收剂量测量并对其进行水吸收剂量因子校准。更换⁶⁰Co γ射线辐射场，用参考剂量仪、针尖电离室剂量仪进行剂量验证测量。结果 参考剂量仪在水下10 cm处，参考条件下测得水吸收剂量结果为0.249 9 Gy。两台针尖电离室剂量仪测量结果分别为0.248 0 Gy和0.250 0 Gy；两台针尖电离室剂量仪测量结果与参考剂量仪测量结果相对偏差均在±0.8%内，针尖电离室剂量仪测量水吸收剂量不确定度为2.8%（k=2）。结论 针尖电离室可用于小野水中吸收剂量的测量。

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 0.249 9 Gy for reference dosimeter, 0.248 0 Gy and 0.250 0 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.