The Design Of Small Gamma Imaging Instrument Based On FPGA

Nuclear technology and nuclide have been widely used in people’s life,for theuse of nuclide brought people a lot of convenience, at the same time also brought a lotof harm to people’s physical health. How to quickly detect the radiation of nuclide inintensity and the location in the environment, ensure the safety of people’s livingenvironment is becoming a hot spot of radiation detection now. Gamma imaginginstrument is a nuclide detection instrument, the instrument, mainly include medicalgamma imaging instrument and environment to detect gamma imaging instrument,etc.This paper mainly discusses the small environment detection is based on FPGAgamma imaging data acquisition system. Due to the requirements of the detection is256channels, according to the randomness of nuclear signal, each channel data maycome at the same time, so the selection of acquisition signal chip, chose the FPGA,this is because the FPGA technology has been widely used in high speed signalacquisition system, and it has the advantages of parallel operation, the ability to256channels of signal is collected at the same time. Normally, our acquisition of nuclearpulse are nuclear pulse detector output signal after preamplifier circuit and mainamplification circuit amplification, with high-speed ADC to gather, this design inorder to simplify the circuit and reduce cost, however, under the premise that thedetection requirements can be implemented, a reference voltage is proposed, which isno longer directly with ADC to acquisition of nuclear pulse, but with a more voltageand the output of the preamplifier circuit nuclear pulse signal, after comparing pulseinto the processing method of FPGA. After comparing the pulse width is100~200ns,we count on each channel of the pulse can detect the position of the radiation in theenvironment and measurement.The design of the detection device adopts Japan marina pine company256anodeH9500photomultiplier tubes,256channels of distribution on the four acquisitionboards, this design by CAN bus to realize the data acquisition module and PCcommunication. Each piece of acquisition boards has a Cyclone III series FPGA asthe core of the information acquisition module and a piece of STM32F103VET6at the core of data transmission. STM32F103VET6internal integration the SPI interfaceand CAN bus interface, and have their respective control required library function, soit is convenient to control, the transmission of data through SPI between FPGA andSTM32, STM32and between upper machine data through the CAN bus transmission.In the aspect of hardware, this paper mainly introduces the FPGA as the core ofthe hardware circuit design, and introduces the reference voltage circuit, amplifyingcircuit, compare circuit, system design and the FPGA configuration circuit CAN buscircuit, etc.In terms of the FPGA logic design, mainly introduced the frequency divisionmodule, the edge of the pulse detection module, data acquisition module, RAMcontrol module, FIFO control module and SPI control module, etc., and introduces thefunction of these modules for the simulation.In the aspect of software, this paper mainly introduces the internal design ofFPGA and FPGA STM32and the realization of communication between uppermachine, mainly used in PC programming Microsoft Visual Studio2005as adevelopment tool.When the data system is completed, we make a practical testing. As the result ofthe test, the system works stability and can achieve the desired results. and the systemhas the advantages of small volume, fasting response speed, being easy to transplant,It has the value to the research of the environment detection.