基于中国参考人体素模型环境外照射剂量转换系数的计算

Dose Coefficient Calculation of External Exposure of Radionuclides Based on Chinese Reference Voxel Phantom

基于中国参考人体素模型计算地面污染和空气浸没情况下环境外照射剂量转换系数,主要用于核事故情况下公众及工作人员有效剂量的快速估算.首先,采用二次源项方法,基于Geant4模拟进入人体周围圆柱面入射光子的高度、角度和能量分布;其次,利用中国参考人体素模型和二次源项结果作为MCNPX模拟的输入项,计算15ke V至10 Me V能量范围内20组单能光子外照射剂量转换系数,和文献数据吻合;最后,利用ICRP第107报告核素衰变程序并对单能光子外照射剂量转换系数进行插值,计算了核事故情况下68种常见核素外照射剂量转换系数.与本文结果对比,国标中用于快速估算人员受照剂量转换系数值在地表沉积情况下偏保守,而空气浸没下中高Z放射性核素则偏低.

Dose coefficients for external photon radiation are widely used for assessment of radiation dose to public and workers due to ground surface contamination and air immersion of radionuclides released in nuclear accidents. Dose coefficients based on Chinese reference voxel phantom were presented. Photons that incident into the cylinder, which is slightly larger than phantom, is simulated using Geant4, including distributions of angle, height and energy of photons; Secondly, photons are sampled on surface of cylinder around Chinese Reference Male/Female Voxel Phantom with MCNPX 2.4.k from the above source, dose coefficients of 20 initial gamma ray energies, from 15keV to 10 MeV, are calculated. Thirdly, dose coefficients of 68 important nuclides are evaluated by combining of decay data from ICRP 107 and photon coefficients using cubic-spline fitting. GB/T 17982-2000 shows an overestimation for ground contamination while an underestimation of high Z nuclides for air immersion compared to our results.