Development Of Large Area Position Sensitive Detector

With the increasing application of nuclear technology, more and more people pay attention to the security of the use of various types of radioactive sources. Strengthen safety supervision of radioactive materials require extensive use of nuclear technology and equipment, the gamma ray imager can achieve fast and accurate positioning of radioactive material by, it play an important role in the field of experimental nuclear physics, particle physics, astrophysics, geological exploration, nuclear medicine,nuclear safety, and so on. In the search process of the radioactive substances, to quick and accurate imaging of radioactive material, to determine the position of radioactive substances, the detector has good position resolution, detection efficiency and sensitivity. Therefore, it is necessary to improve the performance of the detector and design a set of superior performance of the detector. In this paper, a large area position sensitive detector based on coded aperture technique is developed for ultra high sensitivity gamma ray imaging.Encoding collimator and large area position sensitive detector is the core component of ultra high sensitivity gamma ray imager. Code of collimator by the code plate fixed plate and the code plate, the detector is composed of four large volume detector module and sensitive area of each detector module for 165 mm * 165 mm.This is because the ultra high sensitivity gamma ray imaging system is mainly used in the mobile platform, to complete the accurate positioning of the radioactive material,the 4 detector modules to improve the detection efficiency of the array. At the same time, to optimize the design of each module, the module can achieve seamless connection, the whole detector's sensitive area is 330 mm * 330 mm.Development of coding collimator includes coding mode selection and code board and basic unit size determination, code board material, code plate and the code plate of the fixing plate processing. In this paper, the principle of coded aperture imaging is introduced, and according to different coded aperture imaging characteristics, considering the various technical indicators, the modified uniform redundant array coding mode is selected. According to the coding mode and the size of the flash body, the basic unit size of the code board is determined to be 30 mm * 30 mm, a total of 21 * 21 basic units, the overall size of the code plate is 610 mm * 610 mm. Code plate material selection mainly consider the density of the material and of gamma ray blocking ability. Through tungsten powder experiments found that tungsten powder filling density is not up to the requirements, and finally determine the code plate material for 99% of the content of tungsten tungsten copper nickel alloy nugget. According to the design requirements of the gamma ray blocking rate, the design code board thickness is 15 mm, and the processing of the code plate adopts the mechanical processing method to process the tungsten nickel copper alloy into the metal strip. The fixed plate of the code plate is made of nylon material, the size is 710 mm * 710 mm * 30 mm, and the mechanical processing method is adopted.Detector module mainly by the scintillator array, a photoelectric multiplier tube array, optical, reflection layer and front-end electronics(including photomultiplier voltage dividing circuit, position readout circuit, a pre amplification circuit, a timing circuit).The scintillation array adopts 11 * 11 Cs I(Tl) scintillation body, the volume of a single scintillation body is 14.9 mm * 14.9 mm * 14.9 mm, six surface polishing,and a high back film with 0.065 mm thickness. Photomultiplier tube array by photoelectric Beijing Hamamatsu CR173 multiplier tube consists of 3 * 3photomultiplier tube array, and a photomultiplier tube the size of the entrance window of 51 mm diameter and photocathode effective size 46 mm diameter. Through different types and thickness of the light guide experiments to select the 20 mm thickness of the well. The partial pressure circuit of the photoelectric multiplier is designed according to the recommendation of CR173.Select the DPC circuit position readout circuit, 9 photomultiplier tube leads to signal by encoding into 4 signals. Pre amplifier and timing circuit mainly use AD8042 and MAX942 etc chip of Analog Devices(AD)company in the United States.In this paper, the performance test of the photoelectric multiplier tube, the consistency correction of the photoelectric multiplier tube are carried out. Erected after the detector module test platform, on the photoelectric multiplier tube voltage supply, DPC circuit, photomultiplier tube array and experimental study of scintillator array, optical, etc., the detector module of each component of the optimization. The development of a single detector module is completed, and the reliability of the design scheme is verified experimentally. After the 4 identical modules are assembled together to complete the development of the whole detector.