| Contemporary radiation imaging technology is developing rapidly and is widely used in medical imaging,high-energy physics,nuclear industry,aerospace industry and other fields.In the field of neutron detection and neutron imaging,the research and development and application of neutron imaging equipment and supporting components have received continuous attention and research.Among them,scintillators,photoelectric photoelectric conversion devices and electronic systems are the most critical.GdI3:Ce,a new scintillator has great application prospects in the field of neutron detection and neutron photography due to its advantages of largest thermal neutron capture cross section,high luminescence yield,short luminescence decay time,and high light transmittance.Among the photoelectric conversion devices,new semiconductor devices represented by silicon photomultipliers(SiPM/Silicon Photomultipliers)are gradually replacing traditional photomultiplier tubes.Compared with traditional photomultiplier tubes,SiPM has smaller size,lower operating voltage,lower sensitivity to magnetic fields,and higher photoelectric conversion efficiency,all these advantages make it to be the most potential photoelectric conversion devices in the field of radiation imaging.The neutron conversion and photoelectric conversion parts are composed by Gd based scintillator and SiPMs.Because the gain of SiPM is varies with temperature,a small programmable high-voltage power supply is designed and used to correct the drift in gain factor caused by temperature.For the readout method of the SiPM array,two readout methods are used:one is a readout method using multi-channel charge sensitive amplifier to accumulate the energy,another is by counting the events from 64 SiPM channels.Data processing and data transmission is inplemented one FPGA,data is transmitted through the USB interface,and finally the image is displayed on the computer screen.The relationship between the output voltage of the programmable high-voltage power supply and operating temperature of SiPM needs to be determined by spectrum measurement,meanwhile the energy resolution of the Gd-based scintillator detector also needs to be determined.Based on the above requirements,high-performance digital multichannel energy spectrum analysis system is designed,it uses PMT+Nal assembly and 137Cs radiation source to measure the resolution of the energy spectrum analysis system.The resolution(FWHM)of spectrum analysis system is less than 7%,the resolution is excellent and meets the needs.Based on the existing research,the design and optimization of the neutron radiation imaging probe design,the determination of the corresponding curve of the high-voltage power supply output voltage and the SiPM operating temperature,the readout of the SiPM array signal,and the design and optimization of the:energy spectrum measurement system are as follows:(1)Two detectors were assembled for the imaging test system and the energy spectrum test system.The first detector send the signals from SiPM array to the signal processing and imaging system via FPC cable.The second detector is used for energy spectrum test,signals of the SiPM array are added and processed by the front-end amplifier and output to digital multichannel energy spectrum analysis system via coaxial cable,the resolution(FWHM)of the detector is 12.5%(tested by 241 Am).(2)A small programmable SiPM power supply is designed to stabilize the gain drift of SiPM due to temperature change.The self-developed digital multichannel energy spectrum analysis system and 241Am radiation source are used to determine the benefit of the power supply.The measurement results show that after adding the voltage compensation function,the drift of full energy peak of 241Am(59.54KeV γ)was reduced from 110 channels without compensation to 5 channels with compensation between 5℃ to 40℃,which means the gain drift of SiPM due to temperature decreases from 87.3%to 2.76%.When the threshold discriminating method(PHD)is used to discriminate the neutron and gamma,the discriminating threshold value will float caused by the temperature drift of the SiPM gain,the high-voltage power supply with voltage compensation function can effectively mitigate this effect.(3)A high-performance digital multichannel energy spectrum analysis system is designed,it uses PMT+NaI(volume:2L)assembly and 137Cs radiation source to measure the resolution of the energy spectrum analysis system.The resolution(Full width at half maximum/FWHM)of spectrum analysis system is 6.55%,the resolution is excellent and meets the needs.(4)Designed two SiPM radiation imaging electronics systems:energy accumulation imaging system,events counting imaging system.The energy accumulation imaging system includes:motherboard,multi-channel charge sensitivity integral amplifier&ADC board,FPGA drive-readout board,signal processing daughter boards(analog signals in analog signals out).Events counting imaging systems includes:motherboard,FPGA counting board,daughter boards(analog signals in digital signals out). |
