Airborn Gamma-ray Spectrometer System Test And Calibration Method Research

Fruitful research on gamma-ray data processing algorithm and application has done by experts and scholars in the domestic and foreign, however, will be the full spectrum of analytical method applied to the energy spectrum of research system calibration are rarely informed. Can or not use less of the standard model or standard sample for reliable and accurate scattering calibration of gamma-ray measuring system, with more concise way and a certain precision, is worth studying. When new aero-gamma spectrometer in domestic is developed, with the specific performance index is concerned, each index all need through the feasible and effective methods for precision measuring, this is worth discussing. In different testing, system how to respond, in different height range, the rule of different energy gamma rays with height change on waters, ground-launched and sea, all of this is worth researching.This article comes from the national 863 Program, the seventh issue of major projects of resources and environment technoloygy "airborne geophysical exploration technique system"—"Department of airborne gamma spectrometry survey ECR&D" (No. 2006A06A207). This article launched research mainly on main performance testing of airborne gamma spectrometer, the rule of different energy gamma rays with height change in different environment, the calibration approach of system. It firstly introduces main radiation source and its characteristics of airborne gamma ray spectroscopy surve, and the calculation method of eminence above the earth's surface are analyzed and discussed by conical model. Then,deeply analyzes the common natural original spectrum of airline spectrum measurement, the forming process of the spectrum signal, and the complication of the measured instrument spectrum. Finally the paper's main research content and the results are discussed in detailThe main research contents and achievements are as follows: (1) Analyze the main performance indexes and its meaning of spectral instrument. Research the test methods of key indicators In bare crystal and low background, measure the energy resolution under two conditions. In terms of 661KeV energy peaks of Cs source, all the resolutions of single detector in two conditions are less than 8%. Resolution of system is less than 8.4% in the indoor environment. Using many peaks of U and Th, and linear equation of energy, obtained the starting energy threshold which is less than 23KeV. Both the each detector and system's degree of linear fitting of energy are more than 0.9999. The integral nonlinearity is less than 0.2%, and the differential nonlinearity is less than 1.0%. The maximum count rate of system reached 200K/sec. The dead time determination of system is less than 5μs by dual-source net count. Through arbitrary 4 hours data of 24 hours indoor stability testing, relative errors between count-rate of each window and the average count-rate are less than±10%. Among them, the count-rate of TC is less than±6.29%. For 48 hours stability testing, placed the system into outdoor environment where temperature and humidity changes with time, observations show that the count-rate decreases with the ground moisture. In 1024 mode, attune slants 16 channels, and the system will return to good spectrum-stabilizing effect in 90 seconds.(2) Using the data over the water and the land dynamic calibration belt below 300 metres, analyze the count-rate of different energy windows, thereby getting the rule of gamma-ray distribution by enery in low altitude above land and water. Using the data over the sea between 1800 and 3000 meters, analyze the count-rate of different energy windows, thereby getting the rule of gamma-ray distribution by enery in higher altitude above sea.(3) In full on the basis of investigation and analysis, select the method of combining SINP and Fourier transform into deducting the bottom of the spectrum instrument accurately. Then, use direct demodulation method for analyzing the full spectrum. This method is applied to system calibration. By stripping coefficient method and aviation calibration model, demarcate the system of on-board, on plane of Y-5, and on plane of Y-12. Among them spectrum drift seriously in the on-board test, there is a obvious mistake, when spectra drift show more serious, scattering detachment is meaningless. Comparing inverse calculation content of the hybrid model by the two methods, both the relative errors are similar with the recommended value. Demonstrate the full spectrum of analytical calibration gammaγenergy spectrum in the aviation system in the feasibility and accuracy of calibration. Proof the full spectrum analytical calibration method's accuracy and feasibility in the calibration of aiborne gamma-ray spectrometer system(4) Using the method of full spectrum analytical calibration with a single point spectrum and all the data respectively, the calculation results show that using more datas will benefit the inhibiting of statistical fluctuation. By the model of K, U, Th, get a group of conversion coefficient, and another group by the model of M, both a relative error less than 2.2%. So can use a saturated standard model or sample to get conversion coefficients, thus the full spectrum analytical calibration method can reduce the workload of calibration effectively.