X射线装置豁免管理的技术认定方法研究
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摘要
[目的]根据豁免基本准则要求,通过对辐射剂量测量仪器性能的实验研究和屏蔽材料衰减特性曲线蒙卡模拟,建立对X射线装置豁免管理的技术认定方法。[方法]利用防护水平X辐射空气比释动能率标准装置,对市售且具有一定使用频次的8类典型辐射剂量测量仪器在10～60 kV加载管电压范围、不同管电流档的仪器能响和读数稳定性等性能指标进行实验验证,计算校准因子;同时,通过蒙卡模拟计算,建立铅、铁、铝、铜、钨和有机玻璃6种常用屏蔽材料对X射线的衰减特性曲线。[结果]8类辐射剂量测量仪器对10 kV及以下X射线均无响应;对20 kV能量X射线,6类仪器有响应,但获得的校准因子差异明显,范围为0.7～11.1;对于30 kV能量X射线,8类仪器均有响应,但校准因子差异较大;对40 kV能量X射线,8类仪器均有响应,其中6类仪器校准因子已接近1,且不受管电流值改变的明显影响;只有60 kV能量X射线,市售8类辐射剂量测量仪的校准因子均接近1。即使同类型测量仪器,60 kV以下时校准因子随管电压也变化较大,且不与管电压呈线性关系。使用蒙卡程序模拟计算并建立的10～100 kV的X射线衰减特性曲线,可用于对不同能量尤其是40 kV以下能量X射线经特定厚度材料屏蔽后泄漏剂量率估算。[结论]本研究建立了X射线装置豁免管理的技术认定方法:对于加载管电压40 kV及以上X射线装置,可使用满足技术性能要求且经相应能量档校准的测量仪进行检测和豁免认定;对于加载管电压40 kV以下X射线装置,可采用衰减特性曲线估算X射线装置表面0.1 m处周围剂量当量率H*(10)进行豁免认定。
[Objective] The aim of this study is to establish a method for technical validation of X-ray equipment exemption in accordance with the principles of the exemption guideline, through experimental study on key specifications of radiation dose measuring apparatus and Monte Carlo simulation of shielding material attenuation characteristic curves.[Methods] Using a standard device of protective-level X-ray air kerma rate, the performance indices such as energy response and reading stability were tested for eight commercially available typical radiation dose measuring apparatus with pre-set usage frequency, in the range of 10～60 kV loading tube voltage and under different tube current conditions, and calibration factor was also calculated. Simultaneously, the attenuation characteristic curves of six frequentlyused shielding materials(lead, iron, aluminium, copper, tungsten, and polymethyl methacrylate) on X-ray were established by Monte Carlo simulation. [Results] The eight radiation dose measuring apparatus did not respond to X-rays below 10 kV loading tube voltage. For 20 kV X-rays, six types of measuring apparatus responded, but the calibration factors of different apparatus were significantly different, ranging from 0.7 to 11.1. For 30 kV X-rays, all apparatus responded, but the calibration factors varied greatly. For 40 kV X-rays, all apparatus responded, and the calibration factors of six types of measuring apparatus were closed to 1 without being affected by tube current. For 60 kV X-rays, the calibration factors of all selected measuring apparatus were close to 1. Even the calibration factor of the same type of apparatus varied greatly depending on the loading tube voltage, and not in a linear manner. Attenuation characteristic curves for 10-100 kV X-rays were established by Monte Carlo simulation, and the curves were suitable for estimating the ambient leaking dose equivalent rate of the X-ray equipment below 40 kV shielded by materials with specific thickness. [Conclusion] A technical validation method is established for X-ray equipment exemption. For X-ray equipment with a loading tube voltage of 40 kV and above, exemption is granted according to the dose measurement results tested using apparatus meeting technical performance requirements and with corresponding energy category calibrated. For X-ray equipment with a loading tube voltage below 40 kV, exemption is granted according to the ambient dose equivalent rate at a distance of 0.1 m from any accessible surface of the X-ray equipment estimated by the proposed attenuation characteristic curves.
[Objective] The aim of this study is to establish a method for technical validation of X-ray equipment exemption in accordance with the principles of the exemption guideline, through experimental study on key specifications of radiation dose measuring apparatus and Monte Carlo simulation of shielding material attenuation characteristic curves.[Methods] Using a standard device of protective-level X-ray air kerma rate, the performance indices such as energy response and reading stability were tested for eight commercially available typical radiation dose measuring apparatus with pre-set usage frequency, in the range of 10～60 kV loading tube voltage and under different tube current conditions, and calibration factor was also calculated. Simultaneously, the attenuation characteristic curves of six frequentlyused shielding materials(lead, iron, aluminium, copper, tungsten, and polymethyl methacrylate) on X-ray were established by Monte Carlo simulation. [Results] The eight radiation dose measuring apparatus did not respond to X-rays below 10 kV loading tube voltage. For 20 kV X-rays, six types of measuring apparatus responded, but the calibration factors of different apparatus were significantly different, ranging from 0.7 to 11.1. For 30 kV X-rays, all apparatus responded, but the calibration factors varied greatly. For 40 kV X-rays, all apparatus responded, and the calibration factors of six types of measuring apparatus were closed to 1 without being affected by tube current. For 60 kV X-rays, the calibration factors of all selected measuring apparatus were close to 1. Even the calibration factor of the same type of apparatus varied greatly depending on the loading tube voltage, and not in a linear manner. Attenuation characteristic curves for 10-100 kV X-rays were established by Monte Carlo simulation, and the curves were suitable for estimating the ambient leaking dose equivalent rate of the X-ray equipment below 40 kV shielded by materials with specific thickness. [Conclusion] A technical validation method is established for X-ray equipment exemption. For X-ray equipment with a loading tube voltage of 40 kV and above, exemption is granted according to the dose measurement results tested using apparatus meeting technical performance requirements and with corresponding energy category calibrated. For X-ray equipment with a loading tube voltage below 40 kV, exemption is granted according to the ambient dose equivalent rate at a distance of 0.1 m from any accessible surface of the X-ray equipment estimated by the proposed attenuation characteristic curves.
引文
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[14]熊瑛.X射线辐射角及辐射场的测定[C]//第十届全国无损检测新技术学术会议.成都:中国机械工程学会,2007:97-100.
[15]The International Commission on Radiological Protection.Conversion coefficients for use in radiological protection against external radiation:ICRP publication 74[R].Ottawa:ICRP,1996.
[16]NIST.Tables of X-ray mass attenuation coefficients and mass energy-absorption coefficients from 1KEV to 20 MEVfor elements Z=1 to 92 and 48 additional substances of dosimetric interest[EB/OL].[2018-11-01].https://www.nist.gov/pml/x-ray-mass-attenuation-coefficients.
[2]International Atomic Energy Agency.Absorbed dose determination in photon and electron beams:an international code of practice.Technical reports series No.277[R].Vienna:IAEA,1987.
[3]环境保护部,国家卫生和计划生育委员会.关于发布《射线装置分类》的公告[EB/OL].(2017-12-06)[2018-11-01].http://www.mee.gov.cn/gkml/hbb/bgg/201712/t20171214_427933.htm.
[4]The International Commission on Radiological Protection.The 2007 Recommendations of the international commission on radiological protection:ICRP publication 103[R].Ottawa:ICRP,2007.
[5]The International Commission on Radiological Protection.Scope of radiological protection control measures:ICRPpublication 104[R].Ottawa:ICRP,2007.
[6]International Atomic Energy Agency.Radiation protection and safety of radiation sources:International basic safety standards:IAEA Safety Standards Series GSR Part 3[R].Vienna:IAEA,2014.
[7]IAEA.Application of the Concepts of Exclusion,Exemption and Clearance:IAEA Safety Guide No.RS-G-1.7[R].Vienna:IAEA,2004.
[8]The International Commission on Radiological Protection.1990Recommendations of the international commission on radiological protection:ICRP publication 60[R].Ottawa:ICRP,1991.
[9]The International Commission on Radiological Protection.Protection from potential exposure-a conceptual framework:ICRP publication 64[R].Ottawa:ICRP,1993.
[10]International Atomic Energy Agency.International basic safety standards for protection against ionizing radiation and for the safety of radiation sources.IAEA Safety Series No.115[R].Vienna:IAEA,1996.
[11]电离辐射防护与辐射源安全基本标准:GB 18871-2002[S].北京:中国标准出版社,2002.
[12]International Commission on Radiation Units&Measurements.Measurement of dose equivalents from external photon and electron radiations:ICRU Report 47-1992[R].U.S.A.,Maryland,Bethesda:ICRU,1992.
[13]辐射防护仪器β、X和γ辐射周围和/或定向剂量当量(率)仪和/或监测仪第1部分:便携式工作场所和环境测量仪与监测仪:GB/T 4835.1-2012[S].北京:中国标准出版社,2013.
[14]熊瑛.X射线辐射角及辐射场的测定[C]//第十届全国无损检测新技术学术会议.成都:中国机械工程学会,2007:97-100.
[15]The International Commission on Radiological Protection.Conversion coefficients for use in radiological protection against external radiation:ICRP publication 74[R].Ottawa:ICRP,1996.
[16]NIST.Tables of X-ray mass attenuation coefficients and mass energy-absorption coefficients from 1KEV to 20 MEVfor elements Z=1 to 92 and 48 additional substances of dosimetric interest[EB/OL].[2018-11-01].https://www.nist.gov/pml/x-ray-mass-attenuation-coefficients.