Study On The Performance Paramerters Of Radiation Detectors Used In The Unmanned/Manned Aircraft Monitoring

Nuclear safety is a lifeline for the development of nuclear power, the rapid development of China’s nuclear power industry in recent years has put forward higher requirements to nuclear safety. To get the timely radioactive environment of association area after the nuclear accident, a regular time and point radiation detection with high precision achieved by using air vehicles is needed. At the same time, IAEA also noted that the use of aerial survey techniques for environmental monitoring and radiation measurements is a necessary means to response to major nuclear accident similar to Japan Fukushima. Therefore, to meet air radiation environment monitoring requirements of an nuclear accident, this paper do two research works to get the performance parameters of radiation detector for manned and unmanned aircraft platforms respectively.Main research work in this paper is as follows.1) Do theoretical analysis and determine the parameter of y-ray effective detection range based on the theory of mean free path in the condition of aircraft radiation monitoring. Build base model of aircraft monitoring the radiation field, get the conclusion that γ-ray effective detection range of140La (1.5962MeV) is1050meters, and this parameter provided an important theoretical basis for the following study work that constructing effective radiation field model. At the same time, for variance problems of Monte Carlo particle transport calculation, variance reduction techniques such as secondary sources, Russia Roulette and mandatory collision are discussed respectively, and also put forward the equal mass thickness method for constructing radiation modeling.2) Research performance parameters of three different types of small Crystal detectors (NaI, LaBr3, and HPGe) which can be applied to unmanned aircraft nuclear emergency radiation monitoring. First of all, get the law of all kinds of detector effective detection efficiency changing with the radiation radius of the source, the maximum effective detection efficiency basically stable at500meters, which verifies the feasibility of calculating the effective detection range based on the theory of free path. Then, parameter indexes of the three detectors such as effective detection efficiency, energy resolution, and minimum detectable activity were compared. Results show that no matter the radioactive monitoring is ground-based or air-based, effective detection efficiency of LaBr3detector is about16%larger than that of Nal detector, and about eight times larger than the HPGe detector. As to the minimum detectable activity (MDA), the performance of LaBr3detector is better than Nal and HPGe detector. However, the energy resolution of LaBr3detector is comparatively poorer than HPGe. Therefore, using a combination of the LaBr3detector and the HPGe detector can realize the optimal performances.3) Do comparative analysis of the performance of the large crystal Nal detector with different packaging materials used for manned aircraft nuclear emergency radiation monitoring. Four different collocation ways:PAl (with permalloy and aluminum as packaging materials); PC (with permalloy and carbon fiber as packaging materials); AlAl (wuth aluminum and aluminum as packaging materials); AlC (with aluminum and carbon fiber as packaging materials). First of all, make comparative analysis of parameters such as energy resolution, effective detection efficiency and minimum detectable activity for these four detectors. Results show that the energy resolution of AlAl and AlC is better than that of PAl and PC. AlC’s effective detection efficiency is about3%larger than that of AlAl, about28%larger than that of PC, and about32%larger than that of PAl.For minimum detectable activity (MDA), AlC’s performance is the best, and then is AlAl, PC and PAl respectively. After comprehensive comparison of these four kind of big crystal Nal detector with different packaging materials, AlC has optimal performance parameters, it can be used as priority scheme of nuclear emergency gamma radiation measuring detector for manned aircraft. Then, make comparative analysis of the effect of loading way to performance of the detector. Take Pal as example, results show that the count is higher when detector is external, the minimum detectable activity(MDA) is32%more than that of built-in way. Therefore, it is recommended to use external detector model in the process of actual aerial measurement.