针尖电离室水中吸收剂量校准方法研究

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

目的 ^(60)Coγ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^(60)Coγ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^(60)Coγ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。

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.