针对超临界事故中人体受到中子辐照后感生的24Na活度测量，采用MCNP软件建立蒙特卡罗模拟模型，分别模拟不同类型NaI探测器对24Na衰变的两条γ射线全能峰的探测效率和塑料闪烁体探测器对24Na衰变的β射线总计数的探测器效率。模拟结果表明：井型NaI探测器与圆柱型相比，24Na衰变的1.38 MeV和2.76 MeV γ射线全能峰探测效率分别提高了4.30倍和4.11倍；塑料闪烁体探测器对24Na衰变的β射线的探测效率是NaI探测器对24Na γ射线的探测效率的1.72倍；同时粗略计算了探测器计数与人体所受中子辐照剂量之间的关系。

For 24Na activity measurement of human body activated by neutron irradiation in the supercritical accident, the MCNP code is used to create a Monte Carlo simulation model. Two-γ-ray total-energy peak detection efficiency of 24Na decay using different types of NaI detectors, and total β-ray number detection efficiency of 24Na decay using plastic scintillator detector are simulated. The simulation results show that, for the 1.38 MeV and 2.76 MeV γ rays of 24Na decay, the efficiency of the well-type NaI detector is 4.30 times and 4.11 times that of the cylindrical one; the β-ray detection efficiency of 24Na decay using the plastic scintillator detector is 1.72 times the 24Na γ ray detection efficiency using the NaI detector. Meanwhile, a rough calculation of the relationship between the detector counts and the neutron irradiation dose of human body is carried out.