全身计数器用于对人体内照射污染的监测, 对最小探测活度(MDA)有较高的要求。为使全身计数器具备较好的灵敏度, 需要降低本底辐射和提高射线探测效率。基于MCNP5模拟了全身计数器中NaI探测器在不同几何位置时的能量响应, 对探测器位置及准直器角度进行研究, 同时对不同厚度的屏蔽结构进行了仿真计算分析。研究表明, 当屏蔽钢板厚度为14.9 cm时, 能够较大程度地降低本底辐射。在源探结构上探测腔准直器角度在26°以上, 探测器与体模的距离为20 cm时, 能够得到理想的能谱响应和探测效率。

The whole body counter is used to monitor the contamination of the human body and has a high requirement for the minimum detection limit (MDA). In order to have a better sensitivity for the whole body counter, it is necessary to reduce the background radiation and improve the radiation detection efficiency. Based on MCNP5, the energy response of the NaI detector in the geometric position is simulated. The position of the detector and the angle of the collimator are studied. At the same time, the shielded structure with different thickness is simulated and analyzed. The study shows that when the thickness of the shielded steel plate is 14.9 cm, the background radiation can be reduced to a large extent. In the source structure to detect the cavity collimator angle above 26°, when the distance between the detector and the body mold is 20 cm, the detector can get the ideal energy spectrum response and detection efficiency.