Design Of Dual-mode Radiation Dosimeter Based On FPGA

GM counter is widely used in the field of nuclear radiation measurement,but its application in strong radiation environment is limited by its long dead time,pulse accumulation and narrow range.In view of the inherent shortcomings of GM counter,based on the principle of time-to-Count measurement,a one-minute dual-mode radiation dosimeter based on high-speed FPGA core is designed,which effectively expands the range of GM counter,prolongs the life of detector and has high practical valueFrom the aspects of hardware design,software development and performance test,the structure and working principle of dual-mode radiation dosimeter are discussed in detail.The instrument operates in both counting and time modes.Among them,the counting mode is mainly used for the measurement of environmental radiation dose,and the time mode is mainly used for the dose monitoring under strong radiation.The two modes can be automatically switched.The main work and achievements of this paper are as follows:1.The hardware circuit of dual-mode radiation dosimeter based on FPGA is designed.The probe of radiometer adopts J305 GM counter and customizes Nios II soft core processor based on the core of FPGA.It realizes the functions of fast switching of high and low voltage power supply,accurate timing of signal,discrimination of working mode,display and alarm,etc.2.The radiation measurement software based on Nios II soft core processor is developed,which includes automatic mode determination subroutine,time mode subroutine and counting mode subroutine.The functions of radiation dose measurement and control in dual mode are realized.3.The working parameters of the dual mode radiometer are calibrated by standard instrument method.The main performance indexes of the radiometer are tested preliminarily.The applicable conditions of each mode are also discussed.The results show that:(1)In the counting mode,the range of the instrument is 0.4 ?Gy /h~133 ?Gy /h;in the time mode,the range of the instrument is 1.92 ?Gy/h~4800 ?Gy /h;and the time-to-Count method can effectively expand the range of the GM counter,which is more than 30 times larger than the upper limit of the traditional counting mode.The range of the radiometer can span five orders of magnitude.(2)At low dose rate,the maximum relative error of pulse counting method is 9.7%,and that of time-to-Count method is 34.7%.At high dose rate,the maximum relative error of pulse counting method is 50.6%,and that of Time-to-Count method is 8.3%.Therefore,when measuring environmental background and weak radiation field,the counting mode should be preferred;when measuring strong radiation field,the time mode should be adopted,which has the advantages of wide range and small error.