Development And Performance Test Of Key Components Of A High-sensitivity Gamma Imaging System

Radioactive materials have made important contributions to scientific research,medical diagnosis,industrial analysis,and other fields,but they also pose a certain threat to environmental safety,and efficiently detect and monitor the radioactivity and radioactive sources generated by various nuclear accidents.it has become an urgent need to vigorously develop rapid and effective nuclear imaging technology.Nuclear imaging technology can detect the distribution image of radioactive material and overlap with optical images to visually show the location of radioactive material.However,the traditional gamma-ray imaging system has low sensitivity and long imaging time,and it is impossible to image a dynamic target in real time at a long distance.High-sensitivity gamma-ray imaging technology can locate the location of radiation hotspots in real time at a long distance and give a two-dimensional real-time image of the radioactive distribution.When we install the imaging system on a monitoring vehicle or a monitoring boat,we can quickly scan a large area to determine the distribution of radioactive materials.The coded aperture imaging technology greatly improves the detection efficiency of the system through the multi-aperture collimator with specific patterns,and it is also greatly reduced for the imaging time.However,it is not possible to image for relatively long-range radioactive sources or weaker sources in real time,and high-sensitivity coded aperture imaging technology can achieve this function,It is mainly achieved by increasing the effective area of the detector at the international or domestic research level.In this paper,based on the study of the coded aperture imaging theory,the MURA coding method is selected to construct coded mask that array size is 11 × 11.A largearea Cs I(Tl)crystal array with a sampling number of two(22 × 22 detector array)is coupled with a non-position-sensitive photomultiplier tube as a detector with high detection efficiency and high sensitivity.These two parts constitute the front-end detector system for data acquisition.I independently designed a 36-channel analog circuit to amplify and filter the signal output from the anode of the PMT.Subsequently,the multi-channel data acquisition card of the project team was used to complete the digitization and calculation of the analog signal,and the processed data was transmitted to the computer.I used Lab Windows CVI to design the corresponding interface(including energy spectrum,projection matrix,decoded reconstructed image and fusion image of optical camera image and decoded reconstructed image,etc.)and decoding algorithm(direct decoding and iterative decoding algorithm),and the two algorithms are successful applied to the actual prototype.After completing the prototype of the high-sensitivity coded aperture gamma camera,a series of tests were performed on the performance of the detector,including scatter plots(reflecting position resolution),consistency of peak position,energy resolution and consistency of detection efficiency.As a result,it meets the requirements of highsensitivity coded cameras.Then the overall performance test of the prototype was carried out.The test showed that the system has good performance in the detectable energy range,imaging time,angular resolution,etc.The use of positive and negative code plates also reflects its importance in practical application(it further improve the detection ability of low dose rate radioactive materials at high noise floor).The realtime imaging test results show that the prototype can carry out mobile imaging of the radioactive environment and locate the distribution of radioactive materials in real time.Overall,the performance of both the detector and the performance of the highsensitivity coded aperture gamma imaging system have achieved good application results.