Studying on sensitivity of detectors has most guiding significance for the size of detector , the structure of instrument , target element .Through the Boltzmann equation and the electron -transport equation of Spencer-Lewis, the theoretical calculation formula about the sensitivity of detector was acquired .Via the simulation of MCNP5,many laws of the sensitivity of detector were found .The sensitivity of the Si -PIN style detector obeyed exponential increasing rate when the thickness of detector crystal was growing .As the energy of the incident ray increases ,the law of sensitivity is similar to the detector efficiency curve .When the distance between detector and sample is shorter than 100 mm, the influence of distance on the sensitivity can be neglected .%在能量色散X荧光仪设计过程中，探测器的尺寸、系统几何结构和目标元素等都涉及到探测器灵敏度的问题。论文从玻尔兹曼方程及电子输运Spencer－Lewis方程入手推导探测器灵敏度的理论计算公式，基于MCNP5模拟平台研究Si－PIN型探测器灵敏度变化规律。研究发现：Si－PIN型探测器灵敏度随探测器灵敏材料厚度的增加呈指数增长；随入射射线能量增加，其规律与探测效率曲线相同；当探测器与样品间的距离小于100 mm时，距离对探测器灵敏度的影响可以忽略。
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