Development Of α And β Contamination Detector For Hand And Foot Surface

Composite detectors of Zn S(Ag)and plastic scintillator are mostly used as the equipment in detecting α and β pollution on the surface of objects to detect the α and β rays simultaneously.The different ways to discriminate α and β rays result in different effects of surface pollution by different detection instruments.Conventional methods of discrimination are pulse amplitude discrimination and pulse width discrimination,which are affected by the parameters of analog components(forming time of analog circuits)and reduce the effect of discrimination.In this paper,a new method based on digital pulse to process α and β rays is proposed to solve the problems of conventional discrimination.Digital screening circuit adopts analog circuit + FPGA architecture.The analog circuit preprocesses the current pulse output by α and βcomposite detector to meet the requirements of digital processing,and the FPGA processes the pulse signal to complete the discrimination and counting of α and β.After the α and β pulse signals detected by the detector are converted into pulse width signals with different widths by the analog signal adjusting circuit,they are digitally processed by the AD conversion circuit,FPGA and its peripheral circuits to realize the discrimination and calculation of digital signals.The counting information is analyzed and processed by the micro controller and then transmitted to the upper computer for display.The power supply circuit includes three modules: analog power supply,digital power supply and high voltage power supply.The analog power supply is provided by low dropout linear regulated voltage(LDO)power supply,DC-DC conversion technology is adopted to provide the digital power supply,and Hamamatsu’s adjustable high voltage module is used for the high voltage power supply.Microsoft WPF framework technology,visual studio 2017 and C #language are used in program development and design.By constructing current restorer,two-way square filter and ratio calculator in FPGA,the ratio R of output peak value of two-way square filter is calculated to form a normal distribution curve with ratio R as horizontal axis and counting rate as vertical axis.Through the analysis of the Gauss distribution of αand β rays in different intervals of the ratio statistical chart,α and β rays can be discriminated.The performance of the proposed surface contamination detector was tested experimentally and the samples were measured and analyzed.The measurement results show that the method can detect α and β rays in real time,with the quality factor 3.52,and the channel ratio less than0.5%.The detection efficiency of α and β rays is not less than 50.14%and 35.7% respectively,which achieves the expected goal.