The Study Of Gamma Spectrometer Efficiency Transformation Methods From Point Source To Volume Source

HPGe γ spectrometer has the advantages of good energy resolution, stability, and so on. Based on these advantages, the establishment of the γ spectrum analysis technology is becoming one of the most important radionuclide analysis techniques, and it widely used in national defense, nuclear energy, disease control and environmental protection, or other fields. The core of γ spectroscopy technique is to determine the detection efficiency, namely, it is the relationship between the number of photons that determined and the photons are detected with the analysis of samples in actual ejection, usually, the method to obtain the detector efficiency is calibrated by a standard source. However, the sample of the actual source is much more complex than the standard’s, it can’t absolutely agreement both the sample and standard in medium composition, density, and even other aspects of geometric specifications, but the impact of these differences on the detection efficiency is difficult to be corrected by the experimental approach.Based on the rapid development of computer technology, accurate description of the source and the detector measurement, the emitted ray from the measured radionuclide, the sample’s matrix and the role of radiation with detector are simulated by Monte Carlo method, it can obtain the detection Efficiency from the theoretical, and this method has become a hot research. With this simulation method for changing the composition of the source, differences in the sample’s matrix, the Monte Carlo method only need to change a few parameters, and then, the correction calculation can be achieved, beside it can save a lot of money and time compare with the experimental method. But, after all, the Monte Carlo simulation is a estimated calculate method, the accuracy of the input parameters and the accuracy of the description of the role of the process will have an impact on the end result, so the reliability of the final result must be experimentally tested.In this paper, the experimental measurements and theoretical calculations will be combined, on the basis of the result of γ spectrometer efficiency calibration by using the highest level of accuracy and point-like sources, a Monte Carlo method is studied to determine the volume source of γ spectrometer detection efficiency. The specific content as follows:The accurate measurement result of point source detection efficiency in HPGe γ spectrometer. Using 241 Am, 109 Cd, 134 Cs, 137 Cs, 60 Co, 152 Eu and 133 Ba 7 species, which it purchased from PTB, Germany and LEA, France, and the accuracy of these sources are measured by using the standards device in the National Institute of metrology. And these point source’s expanded uncertainty degrees are better than 2%(k=2, 95% confidence level), the point source detection efficiency is obtained by precisely calibrated HPGe γ spectrum.The precise measurement and calibration of HPGe γ detector’s structure and size. In order to accurately describe HPGe γ detectors, two methods are used in this paper, including the CT scan and high-energy γ-rays(60Co, 5000Ci) imaging technology, the detector’s geometry and size are obtained by these method, and it combined with the MCNP program calculates the standard point source detection efficiency, the detector’s geometry and dimensions are optimized, which is obtained by imaging technology, then the dead layer thickness on detector crystal is ensured, and lastly, the optimal physical model of the detector is established.The study of the model of volume source detection efficiency and correction factor calculation. Based on the precision of HPGe γ spectrometer point sources detection efficiency, combined with the detector’s physical model, geometry and matrix, a Monte Carlo method is built, which is used to calculate the HPGe γ spectrometer volume source detection efficiency, and the self-absorption factors and coincidence summing correction factors are researched.Calculating the Φ75mm*70mm volume source’s detection efficiency with the studied Monte Carlo method, and compared with the experimental detection efficiency, which is measured by using the high accuracy standard sources, both results are agree within 3%. Finally, the calculation method’s validity is proved.In the present study, the research’s work can focus on the modeling about various source’s geometric, such as planar, cylindrical and Marinelli beaker, the measured sample’s matrix, the calculation of detection efficiency and related correction factors. Ultimately, we can achieve the goal, that is based on the point source detection efficiency, it can calculate the different geometric specifications, different soil density, ore and ash composition in different matrix radionuclide detection efficiency, and providing technical support for high-precision measurements for various samples of γ radionuclide activity, service in national defense, nuclear energy, disease control and environmental protection, and so on.