Study On Low Background ??? Energy Spectrum Measurement System

With the increasing development of the economy,people pay more attention to green,sustainbale environmental development.After the Fukushima incident in Japan in 2011,the damage caused by radioactive rays to the environment and humans arouse high attention by human beings.The low concentration of ? and ? rays in the environment can cause irreversible damage to humans due to easy adsorption and ionization in human body,etc.,The protection of people's healthy life is urged by our country.At present,the detection of low concentrated ? and ? rays in the world is in the primary state.On the basis of our rapid development of computer and hi-tech industry in China,it is imperative to independently design an efficient and accurate low background measuring instrument.This paper independently designed a low bankground ? and ? rays measurement.This intrument is made by PIPS arry detectors,preamplifiers,multichannel data acquisition boards,high and low voltage power supplies,vacuum systems,instrument chassis,and data processing software.Although the PIPS arry detector is unresponsive for high-energy ? rays,it responses low-energy? rays.As we all know that it is difficlut to separate low-energy ? rays and ? rays due to approximate energy.Hence,this paper carried out based on the theory that low-energy ?-rays and ?-rays can be decomposed by ?-background deduction.Firstly,the PIPS array detector adopts 5 domestic detectors with uniform detection performances and effective detection diameter of ?35 domestic detectors.The detection performance of each PIPS detector is not lower than that of foreign PIPS detectors as the same size.The preamplifier uses a transistor + op-amp structure that simplifies the circuit design of traditional preamplifiers,making the system simpler and more stable.The multi-channel data acquisition board adopts the structure of high-speed ADC+FPGA+ARM.In order to meet the design requirements,this article uses two AD9633-80 with ADI,each of which containing 4 analog input channels,each channel maximum sampling rate of 80 MHz,each channel vertical resolution of 12 bits.The FPGA uses xilinx to introduce the Spartan?-3E series of low-pin count xc3s500 e with up to 500,000 logic resources and up to 368,640 bits of on-chip RAM resources.ARM's STM32F103 series of single-chip microcomputers are introduced due to STMicroelectronics has rich internal functions and peripheral interfaces and complete debugging equipment,which greatly simplifies the difficulty of research and development.High-speed SPI bus interface is used between FPGA and ARM,and the communication speed reaches 9Mbps,which makes the communication between FPGA and ARM more stable and faster than traditional serial communication.In the digital signal processing algorithm,the inverse transformation model of CR circuit and R-C circuit is introduced in this paper,and the original pulse shape recovery processing is effectively processed.The edge of the recovered trapezoidal pulse output after the trapezoidal pulse shaping is better,the flat top is straighter,and the value of the pulse amplitude is more accurate.The high-voltage power module uses the LM3017,an efficient low-side controller driven by TI's external switch.Its input voltage range is 5V to 18 V,and the power supply interface is universal.The output ripple of the high-voltage power supply module is only 7mV under no-load conditions,and the ripple is only 28 mV after the load is connected,so as to meet demand of the high-voltage power supply.The upper computer and the data acquisition board adopt the industrial control bus CAN bus,the communication speed is as high as 1Mbps,and the built-in hardware CRC check guarantees the reliability of data transmission.The host computer software is based on the VS2013 development platform and is developed in C# language.The graphical interface is beautiful and the human-computer interaction is simple and quick.With the cooperation of hardware and software,low background ?,? spectrum measurements are basically achieved.The test results show that the background ?,? spectrometer developed in this paper can obtain the original energy spectra of the five PIPS detectors and the anticoincidence spectra corresponding to the four main channels.In the measurement of self-made large-area surface source,atmospheric pressure,the measurement time is 1022 seconds,the total number of PIPS1 channels is 245943,and the total count difference with its anti-coincidence channel is 932,which means the corresponding anti-coincidence ratio is 0.39%;the total number of PIPS2 channels is 210629,and the total count difference with its anti-coincidence channel is 850,that is,the corresponding anti-coincidence ratio is 0.40%;PIPS3 channel's total is 234210,and the total count difference with its anti-coincidence channel is 916,that is,the corresponding anticoincidence ratio is 0.39%;PIPS4 The total number of channels is 161,505,and the total count difference with its anti-coincidence channel is 737,which means the corresponding anti-coincidence ratio is 0.46%.It can be seen that the anti-coincidence ratios of the four main channels and anti-coincidence channels are basically the same.The results indicate that this instrument is successfully developed and can be used practically.