基于蒙卡模拟方法的便携式现场肺计数器理论研究

Theoretical research on on-site portable lung counter using Monte Carlo simulation

目的为了研究便携式探测器是否可用于核事故现场内污染的快速筛查,需要对肺计数探测器的探头类型、探测效率、探测灵敏度、测量距离等技术参数与测量方法进行预先理论研究。方法利用蒙特卡罗粒子输运模拟程序(Monte Carlo N-particle code,MCNP),建立包含肺组织的简易躯干数学模型,将均匀分布在肺组织的典型放射性核素作为模拟辐射源,模拟计算高纯锗(high purity germanium,HPGe)和碘化钠[NaI(Tl)]两种探测器在不同胸壁厚度、不同测量距离下的探测效率,计算探测器的最小可探测活度,即探测灵敏度,通过比较分析,了解适用于现场便携式内污染计数器的技术参数与测量方法。结果计算获得了典型核素内照射情况下两种探测器的探测效率和最小可探测活度。结论初步确定了现场内污染肺计数器的关键技术参数和测量规律,便携式探测器可用于核事故现场内污染的快速筛查。

Objective To theoretically pre-study such parameters as the detector type,detection efficiency,detection sensitivity,and measurement distance of the lung counter in order to determine whether the portable detector can be used for measurement of internal radioactive contamination in the event of nuclear accident.Methods By using the MCNP(Monte Carlo N-particle code,MCNP)and the simple torso mathematical phantom containing the lung tissue that was constructed in this study,the lung with uniform distribution of typical radionuclide was used as the internal radiation source.Then,the high purity germanium(HPGe)and NaI(Tl)were respectively placed outside the torso phantom to study the detection efficiency under different thicknesses of the chest wall and different measurement distance.The minimum detective activity,also known as the detection sensitivity,was determined.In the end,the on-site measurement methods and key parameters of the portable lung counter were investigated via comparison and analysis.Results The detection efficiency and minimum detective activity of the two detectors for typical radionuclide internal irradiation were calculated.Conclusion The key parameters and ways of measurement of the on-site lung counter for internal radiation contamination are tentatively determined.The portable field detector can be used for quick detection of internal radioactive contamination.