The Simulation And Study Of Locting Methods For Radioactive Sources Based On Cylinderical Detector

With the rapid development of nuclear science and technology,the radioactive sources and radiation devices have been wildly used in industries.However,there are amount of sources have had been stolen and lost in the environment which could possibly causing serious damage to people because the lack of scientific and effective management to sources.Therefore,it's quite important to locate the missing sources and reduce potential harms caused by radiations.There are certain advantages as to traditional methods to locate radioactive sources,but they don't performance well in high-precision positioning task.The directional gamma detector is able to resolve the direction of incident gamma rays within a certain distance that would be used for locating the position of lost radioactive sources.Based on the advantage of direction finding detector,we developed two types of directional detector of gamma rays for locating radioactive sources.The main contents of this paper are divided into two parts as following:(1)Three –Crystal Coupling Directional Detector of Gamma raysThis paper completes the basic design of three-crystal couplingdirectional detector of gamma rays and used MCNP to simulate some of the detectors coefficients.It is also discussed the influence of angular resolution which caused by detector volume,air dose rate,energy of gamma beam and other factors.Additionally,simulated the spatial radioactive source location experiment with MCNP and the positioning deviation was analyzed.The MCNP simulation results show that when the optimized crystal-lead radius rate is approximately 1,the directional detector has better performance of angular resolution;under the same conditions,bigger-sized detector has better performance.For the source like 137 Cs,the positioning angular deviation of detector is less than 0.99 degrees when the air dose rate 0.331?Gy · h-1;for the source like 60 Co,the positioning average angular deviation of detector is about 0.46 degrees when the air dose rate is 0.586?Gy · h-1.The positioning deviation of3.7 107 Bq 137Cs source at a distance of 7 m and height of 4 m is about5%.(2)Four-detecting-unit directional detector of NaI crystalThe article completed the basic design of four-detecting-unit directional detector of NaI crystal,and used MCNP simulated the angular responds of every detecting units of detector.In order to locate radioactive source as quick as possible,this paper designed the two different positioning algorithms of fuzzy logic algorithm andtrigonometric algorithm with the angular responding curves of four detecting units.The results show that both of locating algorithm could quickly resolve the incident direction of gamma rays in radiation area,the angular responds are stable and the performance of both algorithms could be better under the condition of bigger-sized detector which is capable of improving the angular resolution of detector.The locating results indicate that using fuzzy logic algorithm to locate source like 137 Cs where the position is(50,200),the relative deviation is less than 8.3%;under the same condition,the relative deviation of trigonometric algorithm is less than 4.2%;for the spatial source of 137 Cs that coordinate is(50,200,200),the relative deviation of fuzzy logic algorithm is 3.31%;the relative deviation of trigonometric algorithm is 2.53%.These directional gamma ray detectors that designed are capable of locating radioactive sources and the techniques of directional detector could be helpful to the nuclear emergency accidents in the future.