Research On Mutual Effect Of Airborne Gamma Array Detector's Response

Airborne gamma ray spectrum measurement is an important means of uranium resource exploration or emergency Radiation monitoring.It has obvious advantages such as high efficiency and low cost.In order to improve the sensitivity and measurement accuracy of airborne gamma ray spectrum measurement technology,the use of high energy resolution gamma ray detector is the development direction.In the domestic and international markets,commercial airborne gamma spectrometers generally use large volume NaI?Tl?crystal scintillation with an energy resolution of about 8%(FWHM@¹³⁷Cs source 0.661 MeV)and a single crystal volume of100×100×400mm³.In order to ensure the accuracy of the ground measurement within a limited sampling time,the probe of the airborne gamma spectrometer uses array with 4crystals or 8 crystals.At present,some new gamma ray detectors with higher energy resolution have been commercialized.For example,the energy resolution of strontium bromide crystals can reach about 2%,and the energy resolution of strontium bromide crystals can reach about 4%.The maximum volume of the germanium crystal is only about×75×75 mm³,while the volume of the strontium bromide crystal is smaller,only about 50×50 mm³.If the energy resolution of the aviation gamma spectrometer increase to 4%,and the accuracy of ground detection is ensured,only a 10×10 array of new scintillation crystal array can be used to increase the volume of the airborne gamma ray spectrum detector.As the size of the detector array expand,the problem of spectral mutual effect becomes obvious.On the one hand,the problem of mutual effect affects the resolution of the characteristic peaks in spectrum and increases background count.On the other hand,if the particles of each detector in the array detector and their energy can be simultaneously recorded,The eliminate Compton scattered photon counts to compensate for full energy peak technology is used to improve the ratio of full energy peak counts to Compton scatter counts,and the resolution of the characteristic energy peak is improved.Therefore,it is important to explore the energy deposition process of gamma photons between array detectors.By establishing the energy deposition distribution model in the array detector,the energy deposition energy spectrum of the gamma ray incident array detector with arbitrary energy in the adjacent detector can be obtained,and the detector instrument spectrum can be corrected.The research content of this thesis comes from the national key research and development plan“High-resolution aerial gamma spectroscopy and airborne imaging spectroscopy”?project number:2017YFC0602105?and the National Natural Science Foundation“High-resolution airborne gamma array detector group energy”.Spectral Response Study"?Project No.41774147?.This thesis has important scientific significance and practical value for the study of mutual effect.In this paper,the mutual effect of array detector's response is studied by theory,Monte Carlo simulation and physical experiments.The main research results are as follows:?1?Through the analysis of array detector and the interaction mechanism between gamma photons and matter,the transport process and energy loss mechanism of gamma photons in the array detector are obtained.?2?The energy of the airborne gamma spectrum measurement?0.661MeV,1.173MeV,1.332MeV,1.46MeV,1.76MeV,2.62MeV?is used as the energy of the source ray.Through the simulation model,the incident point is set at the main detector.The bottom surface moves in three directions and the full-spectrum count of the main detector in the three directions and the full spectrum count curve of the side detector are obtained.According to the curve characteristics,the full energy peak counts of the main detector is quadratic with the distance from the origin.As the curve changes,the full spectrum count of the side detector decreases with the increase of the distance between the incident point and the side detector,and the overall trend of the quadratic function curve also changes.According to the simulation results of the left and right detectors,the points of the left and right detectors are counted.Symmetrical about the Y-axis;based on the single-energy 1.173MeV and 1.332MeV and dual-energy ⁶⁰Co analog count distribution curves,it is proved that the dual-energy incident mutual effect of response can be calculated by the single-energy incident result,and the relative error is 4%.?3?A physical experiment model was established to verify the existence of the mutual effect of response of the array detector.When the narrow beam ray is perpendicularly incident on the bottom surface of the main detector,there is a count on the full spectrum of the side detector.As the incident ray energy increases,the mutual effect of response of the array detector is more severe.?4?Comparing the experimental data with the simulated values,the experimental and simulated normalized count curves are the same,and the relative errors are all within 8%.Using the ratio of the full-spectrum count of each point-side detector to the full-energy peak count of the main detector,the correction factor of the simulated value is calculated.The relative error between the corrected result and the experimental result is mostly less than 10%.Based on the factor simulation data,the modified ¹³⁷Cs and ⁶⁰Co source array detector crystal energy deposition distribution model and the 1.46MeV,1.76MeV,2.62MeV analog array detector crystal energy deposition distribution model were established.