| Analysis ofγ-ray spectrum is a very important method in the measurement of radioactivity. In the naturalγ-field , usingγ-ray spectrometer can directly measure the content and specific activity of Uranium, Thorium and Potassium in the ores or rocks, and then carry out the exploration of radioactive mineral resources and investigation of radiation environment ; In the field of artificial radiation, especially in the large area of radionuclide pollution,γspectrometric surveying can quickly and efficiently determine some information of radioactive sources or pollution sources, such as the location, radiation intensity, and nuclide types.Airborneγ-ray spectrometer generally adopts a number of large volume NaI(Tl) scintillators as a detector, which is due to the airborneγ-ray spectrometry carried out at high altitude(60m~200m), high-speed(60m/s) conditions. In this case, the exposure rate ofγ-ray in the air is smaller, the instrumental counting rate is lower, and as a result, the statistical error is larger, the signal is easily submerged by noise or statistical fluctuation, multiple parallel-operating detectors are equivalent to increasing the effective volume of the detector, and then raise their detection efficiency. At present, NaI(Tl) crystals are generally 10.16cm×10.16cm×40.64cm, usually 5 crystals like these are formed to an array and loaded into a box as the basic detector array of airborneγ-ray spectrometer. And a set of instruments are composed of 1-3 detector arrays, so as to further improve the sensitivity ofγ-ray spectrometer.Because technical target of each crystal can not be exactly the same, and parameter indices of subsequent electronic components are not the same, so the output signals of various crystals have significant differences, That is, instrumental spectrum of each detector is different form the other. Therefore, in the airborneγ-ray spectrometry, it is necessary to synthesize data of the energy spectrum outputted by more strips and more boxes of crystals in accordance with a certain way (that spectrum synthesis), so as to explain and deal with the data of the energy spectrum.This thesis derives from the national "863 Program" major issue——"the R & D in exploration systems of airborneγ-ray energy spectrum" (2006AA06A207), which aims to solve multi-detector's synthetic methods and technologies ofγ-ray energy spectrum for the main control system of airborneγ-ray spectrometer which is Chinese first self-developed , and which provide basic technical support for the whole systemic R & D. The synthetic technology of multi-channelγ-ray instrument spectrum is not only surreptitious in foreign, but also publicly unreported in the publications at home.This thesis is on the basis of the theory ofγ-ray instrument spectrum, and by analyzing the mechanism ofγ-ray instrument spectrum, the differentγ-ray instrument spectrums are regarded as having the same energy value on the same road site when they achieve to different instruments after being translated and transformed scale, then make various instrument spectrums unification. According to the elements as mentioned above, three methods have been proposed, synthesis of translation, synthesis of characteristic peak and synthesis of sampling rate conversion, by which achieve initially to synthesize instrument spectrums of different detectors.This paper focuses on the method of sampling rate conversion in the digital signal processing,which means making "unification" of theγ-ray instrument spectrum by transformed, and then, add up the data transformed in order to obtain generated data. The concrete method is to see the table spectrum data as "Long-lost energy signal" on the energy stalk, and to build the relation model between digital signals and spectrum data because that corresponding data of each long-lost energy signal is the pulse count of an energy segment of two long-lost energy points.Make use of the Matlab software to transform the naturalγ-spectrum by the method of sampling rate conversion, and add up the counting rate of the data transformed corresponding to each road site in Excel, in consequence, generate the new sequences which are data of synthetic instrument spectrum measured form many crystals. The result of testing experiment makes clear that the synthetic effects of sampling rate conversion is the best in the three methods. As for 1024–channel's data of instrument spectrum, the road site of omnipotent peak whose energy is 1.46 MeV moves not over one road site, and less than two for the 2.62 MeV. Meanwhile, error in the clean area of the K peak is smaller than 0.5%. In a word, the technical targets basically meet accuracy request in the measurement of airborneγ-ray spectrum.In the last place, the experiment is accomplished in which the method of sampling rate conversion is applied to synthesizing data ofγ-spectrum which are measured by the several detectors working in condition of different hours, different temperatures and locations. The result indicates that the technical targets of synthetic spectrum are all in the range of the resultant error mentioned above in the synthetic experiment under different conditions, no matter how many detectors are, for example, four or eight. And the result also reflects the sampling rate conversion as a synthesis method haves validity, expansibility and superiority.Therefore, the method of sampling rate conversion can be applied to synthesizingγ-spectrum measured by the several detectors in the airborneγ-ray spectrometer, can carry out synthesize ofγ-ray instrument spectrums measured by different detectors.
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