人体感生24Na比活度测量的几何探测效率优化

Optimization of Geometric Detection Efficiency for Measurement of 24 Na Specific Activity in Human Body

通过测量人体24Na比活度可评估受照射人员的中子剂量,为降低中子剂量的探测下限,可提高γ探测器的几何探测效率,优化γ探测器的位置。利用MCNPX模拟不同照射几何条件下人体中24Na的空间分布,并模拟了24Na特征γ射线在体表的注量分布,最终选择人体背部中间靠近肝脏的位置进行测量。研究结果表明:当252Cf中子辐照剂量为100 mGy时,人体产生24Na的个数为(3.63~4.35)×109,使用晶体尺寸为φ 5×3 cm3的HPGe探测器在10 min内,对能量为1.369 MeV的24Na特征γ射线,可测量的计数不小于2.56×103,中子剂量的探测下限从~100 mGy降至小于1 mGy。

The neutron dose to the human body can be evaluated by measuring the characteristicγray radiation intensity produced by the decay of 24 Na in the human body.The lower detection limit in this method can be further improved by optimizing the position of gamma detector.The MCNP program is used to simulate the spatial distribution of 24 Na in the human body under different irradiation geometric conditions,and the fluence distributions of 24 Na characteristicγrays on the body surface are simulated.Finally,the position near the liver in the middle of the human back was selected for measurement.The research results show that when the irradiation dose of 252 Cf neutrons is 100 mGy,the human body will produce 24 Na isotopes with specific activity of(3.63~4.35)×109.An HPGe detector with a crystal size ofφ5×3 cm 3 is used to measure the characteristicγray of 24 Na with an energy of 1.369 MeV,less than 2.56×103 counts can be measured within 10 min,and the detection limit for neutron dose has also decreased from~100 mGy to less than 1 mGy.