The reaction rates of uranium in the Natural uranium decomposition simulation device is the important data for studying the reliability of neutronics design in the conceptual design of fission cladding in subcritical re-actor.The detect efficiency for annularity source in a HPGe spectrometer must be calibrated accurately.We want to apply the Monte-Carlo method to calibrate the efficiency for annularity source and improve the accura-cy and efficiency.The detect efficiency curve of point source was measured at the axis of the detector with a 6cm distance from the surface.The results are obtained by calculation in MCNP5 and the measurements are fit well through adjusting the size of dead layer and hole in the HPGe.Then the detect efficiency for the annularity gamma source is calculated and compared with the measurement result which was measured by integral calculat-ing the point detect efficiency in radial direction, and the comparison will examine the efficiency calibration method.The measured full energy peak efficiency for the annularity gamma source agreed with the simulated value to within 4%in the energy range 200 to 1400 keV.The method is an accurate and efficient way for cali-brating the annularity source.%天然铀分解模拟装置中铀的相关反应率是研究混合堆包层设计宏观中子学的重要数据，采用活化法测量相应反应率的过程中必须对环状天然铀箔片的探测效率进行精确刻度。为了研究快速有效刻度HPGe探测器探测效率的方法，利用一系列标准伽马点源测量了轴线上6cm高度位置的点源探测效率曲线，在蒙特卡罗程序MCNP5中调整探测器内部结构参数，同时对HPGe探测器的探测效率进行模拟计算，在计算结果与实验结果能较好拟合的情况下推算探测器的死层厚度、冷指长度和半径等参数的实际尺寸。利用计算的尺寸模拟计算探测器对环状伽马源的探测效率，计算结果与实验结果在较宽能量区域（200～1400 keV）内在4％内符合。
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