Design Of A Multi-Sample, Low-Background Tap Water Radioactive Detection

The radioactive contamination in the water is closely related to our daily life. Our new version of the "standard of drinking water" (GB5749-2006) is formally implemented in 2007, and total alpha, beta, radioactive indicators in drinking water were specified in it. This is to protect people’s health and living standards, in the form of laws and regulations to limit various influential factors to human body health in water, the radioactivity in water is one of the important points. Accurate measurement of total alpha, beta activity is related to everyone, so it is particularly important.Traditional total alpha, beta detectors use the design of analog circuit, by using a variety of analog circuits for nuclear signal acquisition and processing, thus suffering from a variety of effects:first, poor anti-jamming performance of analog circuits, the inherent temperature drift, so affected the stability of the whole system; Secondly, analog filtering ability is limited, may not be able to meet the required filter requirements; Again, the analog circuit of system may not be applied to more complicated place; Finally, analog circuit system of dealing with the complicated situation, often needing a lot of analog circuit components, so that increases the burden and the volume of the system.And traditional total alpha, beta detectors in the analysis of the total alpha, beta activity, can’t effectively conduct nuclide screening.Therefore, Chengdu Xing Yuan measurement and control technology co., LTD., established the design of the digital water testing instrument, hoping to turn digital spectroscopy technology used in tap water total alpha, beta test, and realize nuclide screening. With the help of high count rate multi-wire proportional counter, and because of the strong alpha energy, and weak beta energy, we can distinguish between alpha and beta through the spectrum in different parts of the addresses. Then in the region, through the graphic area computation, we can know the total alpha, beta activity. Because the energy spectrum analysis method was adopted, we can conduct the nuclide screening.Total digital alpha, beta detectors involves the intersection of multiple disciplines, is a large engineering, this topic is mainly about the design of electronics parts, especially the research and realization of the various algorithms in FPGA. The main content of this paper is as follows:(1) Understanding of the structure of the digital total alpha, beta detector, work on digital signal processing in the FPGA:the trapezoidal shape filtering module of nuclear pulse signal, rapid trapezoidal shaping module, using the threshold value method to judge whether the nuclear pulse signal module, the position of nuclear pulse signal module, accumulation of nuclear pulse signal processing module, nuclear pulse signal amplitude extraction module and so on.(2)Design of data acquisition card:signal conditioning circuit, power circuit, AD sampling circuit, control chip circuit, data transmission circuit and PCB layout drawing.(3) Design of the communication modules:simple SPI module design in FPGA, SPI module programming in MCU, USB module programming in MCU.(4) Related tests of the electronics circuit:digital signal processing in the FPGA, the communication of FPGA and MCU, the communication of MCU and PC, the whole electronics circuit.To sum up, this topic is about the improvements of the traditional total alpha, beta detector, by using the method of digital spectral acquisition system to improve the traditional total alpha, beta detector, through the powerful flexibility of FPGA to customize the suitable algorithm design, laying the foundation for further study.