K荧光辐射场MC模拟与能谱测量分析

MC Simulation and Energy Spectrum Measurement of K Fluorescence Radiation Field

K荧光辐射装置可填补国内超大型测量面积核辐射探测器计量检定需求,该装置具通量高、能量点多、单色性好、有成本低、即开即用等优势。其原理是X射线光机发射出的X射线轰击辐射体材料产生多种特征X射线即荧光射线,在荧光射线出射路径上加入次级过滤器吸收掉多余的射线以提高荧光纯度,辐射体以及次级过滤器的材料厚度值与荧光产额、纯度直接相关。通过MC(Monte Carlo)程序计算荧光装置各项指标参数结果,指导后期试验装置的建立和研究,MCNP5(Monte Carlo N Particle Transport Code)软件模拟Cs_(2)SO_(4)辐射体数据表明:荧光装置具有良好的屏蔽和准直的效果,荧光以辐射体中心垂直面呈对称逐渐减小分布;荧光产额随着辐射体厚度的增加逐渐增大,但存在相对饱和厚度值,即辐射体达到一定厚度值以后,荧光产额不再随辐射体厚度的增加而增大,而是趋于饱和状态;为获取单一能量荧光辐射场,在荧光出射束方向增加次级过滤器TeO_(2)材料,其吸收L,K_(β)K_(β)射线会远远大于K_(α)射线,以达到消除L,K_(β)射线保留K_(α)射线目的,形成单能的参考辐射场;在距离辐射体中心30 cm处,通过多组数据表明,次级过滤厚度为0.035 cm时,荧光纯度94.521%为最大且荧光产额最高;荧光纯度随着次级过滤器材料的厚度增加呈现先增加后逐渐减小的趋势;使用LEHGe探测器实际测量获取K荧光辐射装置能谱数据,通过ROOT程序对测量能谱数据处理和分析,拟合出K_(α)1和K_(α)2能量点的峰位道址误差小于0.005%,测量分析出其能量值与理论值偏差分别为0.19%,0.23%,测量结果与实际理论能量值相符。测量结果可验证MCNP5程序计算出的次级过滤器材料具有良好吸收效果且实现了单能荧光参考辐射场。

K fluorescence radiation device can fill the metrological verification needs of super large measuring area nuclear radiation detector in China.The device has the advantages of high flux,many energy points,good monochromaticity,low cost and is ready to use.The principle is that the X-ray emitted by the X-ray machine bombards the radiator material to produce a variety of characteristic X-rays,namely fluorescent rays.A secondary filter is added to the fluorescent ray emission path to absorb the excess rays and improve fluorescent purity.The material thickness of the radiator and the secondary filter is directly related to the fluorescent yield and purity.The results of various index parameters of the fluorescent device are calculated by the Monte Carlo program to guide the establishment and research of the later test device.The data of Cs_(2)SO_(4) radiator simulated by MCNP5 software show that the fluorescent device has good shielding and collimation effect,and the fluorescence is symmetrical and gradually decreases in the vertical plane of the radiator Center;The fluorescence yield increases with the increase of radiator thickness,but there is a relative saturation thickness;In order to obtain a single energy fluorescence radiation field,a secondary filter TeO_(2) material is added in the direction of the fluorescence beam,which absorbs L and K_(β)The ray will be much greater than K_(α)Radiation;When the thickness of the secondary filter is 0.035 cm,the fluorescence purity of 94.521%is the maximum and the fluorescence yield is the highest;The fluorescence purity first increases and then decreases with the increase of the thickness of the secondary filter material;The energy spectrum data of K fluorescence radiation device is obtained through the actual measurement of the detector,and the energy spectrum data is processed and analyzed by root program to fit K_(α1),K_(α2).The peak location error of the energy point is less than 0.005%.The deviation between energy value and the theoretical value is 0.19%and 0.23%respectively,and the results are consistent.The measurement results can verify that the secondary filter material calculated by the MCNP5 program has a good absorption effect and realizes the single energy Fluorescence reference radiation field.