Study On Radiological Source Location Based On Three NaI(Tl) Crystal Detector

With the rapid development of China's economy,the application of nuclear technology is widely used in industry,agriculture,medical care,education and scientific research and other fields.The extensive use of radioactive sources and radioactive isotope sources has provided an important impetus for the economic development and social progress of our country.However,radioactive accidents caused by the loss of radioactive sources also occur from time to time.Some of these accidents not only pollute the ecological environment,but also endanger the health of the public.If the radioactive sources are lost to the society for a long time or used by illegal persons for criminal activities,it will inevitably lead to the people's core principle of fear and affect the normal order of society.Therefore,how to locate the missing radioactive sources accurately in a short time is an urgent problem.The directional detector used to detect gamma rays has the advantage of high orientation accuracy.It can distinguish the ray incidence Angle through several measurements within a certain distance,and then obtain the direction information of the radioactive source more accurately.Based on this advantage of the gamma ray directional detector,this paper designed a gamma ray directional detector with three NaI?Tl?crystal detector for the location of radioactive sources.The main content is divided into the following two parts:?1?model design and simulation of three NaI?Tl?crystal detectorsIn this paper,the model design of three NaI?Tl?crystal detectors was completed,and monte carlo method was used to simulate the situation of three detectors in single source radiation field.The influence of detection distance,crystal size and ray energy on the angular resolution is discussed.The location of the three detectors in the single-source and dual-source radiation fields is simulated,and the radiation sources in the multi-source radiation fields are distinguished.Simulation results using the MCNP5 program show that the designed three NaI?Tl?crystal detector can determine the direction of the incident ray in the radiation anomaly region.The influence of the distance between source and detector on the Angle resolution can be effectively eliminated by using the all-around peak proportion method.To a certain extent,increasing the crystal size can better solve the problem of locating radioactive sources with weak source strength.The angular resolution is good for radiating sources that cannot radiate energy.The three NaI?Tl?crystal detector was positioned in the single-source radiation field.For positioning in a single source radiation field,for a ¹³⁷Cs source,the three NaI?TI?crystal detector at the air absorption dose rate?7.31×10^3-?Gy/h,the positioning angle deviation is 0.69°,the relative position deviation is about 2.6%;the mixing of the ¹³⁷Cs source and the ⁶⁰Co source When the radiation field is positioned,the detector is at the air absorbed dose rate?5.21×10^2-?Gy/h,the positioning angle deviation of the ¹³⁷Cs source is 0.96°,the relative position deviation is about 6.5%;the positioning angle deviation of the ⁶⁰Co source is 0.81°,and the relative position deviation is about 2.8%;The radiation field generated by multiple radioactive sources can be distinguished by the type of the radiation source,and the two radioactive sources separated by about 10 cm are better distinguished.?2?experimental verification of three NaI?Tl?crystal detectorsThe design experiment verified the reliability of the positioning of the three NaI?TI?crystal detectors.The experimental analysis of the direction response of the three detectors to the incident particle direction,the influence of the source and detector spacing on the angular resolution,and the radioactive source localization experiment.The experimental results show that for the 1.36×10⁶ Bq ¹³⁷Cs source,the angular deviation of the detection distance from 240 cm to 400 cm generally shows a relatively stable situation,indicating that the omnipotent peak ratio method can better eliminate the source-detector spacing.The effect of angular resolution;in the radioactive source localization experiment,the center of the ¹³⁷Cs source of 1.36×10⁶ Bq is about 2.58 m from the center of the three detectors,the maximum angular deviation measured is?1.72°,and the relative deviation of the positioning position is 3.71%.