| At home and abroad, many researchers have done the calibration of detector efficiency, there are many methods can be used, and there are predecessors of using the Monte Carlo method to achieve the calibration of point-source detection efficiency, some previous numerical analysis methods used for point source and disk source detection efficiency to achieve the calibration. While in this area has a lot of research, but these results are mainly for the detector and the source of a relatively fixed position to scale, emphasis on study of changes in spatial location and angle of impact on the detection efficiency,and the study of different sizes, different size detectors for the detection efficiency rarely. Looking at the results of previous studies, in the field of using Monte Carlo method to calculate the response function of the ray in the detector and to calibrate detection efficiency, Monte Carlo method provide our studies with a greatly facilitate and reduce the large amount of experimental work. However, the application of this method to stay in the use of common software packages of many foreign countries, and comparison of domestic studies has not yet successfully developed procedures for our user-friendly,and few studies to the relationship between the detection of crystal size and the detection efficiency.This article comes from the national 863 Program, resources and environment technology, major projects, "Department of airborne gamma spectrometry survey EC R & D" issue(No. 2006AA06A207) and National Natural Science Foundation project" Nuclear natural gamma geophysical field research "(No. 40774063). The starting point is to explore the different sizes and specifications of the detector with the relationship between the detection efficiency. With a view to play a guiding role of theory for the design of the detector and can be effectively applied to the effciency calibration without source. The main research contents and significance are as follows:1) Calculated using the Monte Carlo method to exploreγ-ray in the NaI (Tl) crystal detector response function of the energy spectrum, and compare the calculated response to the measured spectrum with theγray spectrometer to be the difference between the spectra, simulation of different sizes to detect crystal changes in the relationship between response function.2) Calculated using Monte Carlo simulation ofγ-ray detection efficiency matrix in the detector, and analyze the relationship betweenγ-ray's energy ,detector sizes and the detection geometry of space with the detection efficiency.3) In vc++6.0 development platform, the preparation of a software ,in which, can simulate the response function and calculate the detection efficiency, achieve different sources energy and different geometric parameters of the space probe can be entered in, fast simulation, the analysis can easily see the realization of spectral lines and preservation of the efficiency of matrix-friendly with the interface.4) According to the detection efficiency matrix, research to determine the size crystal for different efficiency calibration of the fitting function and its parameters through the statistical processing software to achieve the rapid detection efficiency curve fitting, and the results of analysis for the study.5)Of airborne gamma measurement applications in the large crystal detectors conducted a preliminary study, simple simulate a square-shaped crystal response function, and calculate the number of square-shaped crystals of different combinations of the detection efficiency, for future use of the detector methods have played a certain role in theoretical guidance.Content of the studies mentioned above, the issue is basically to achieve the desired purpose of the study and achieved better results on theγ-ray spectrum of air and ground-basedγ-ray spectrum probe design work,and play a guiding role in the scientific resources the field of environmental technology and radiation of nuclear resources, environmental monitoring survey has important practical value.
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