Design Of Portable Detection Systems Of Radioactive Activity In Food

Nuclear Science and Technology has been widely used in the military, energy, medical, industrial, agriculture and other fields since 1896, when the French physicist Becquerel found natural radioactivity for the first time. However, while the nuclear science and technology brings us a great benefit, it also brings worldwide nuclear accidents and nuclear terrorism, which threaten people to huge nuclear panics.Nuclear contamination can be spread through water, air and other media when the radiation emergency happens, and it will take a long time and great efforts to eliminate the contamination. Nuclear contamination can cause damage to human life directly, what’s worse, it causes long-term serious pollutions to the ground, water and air. As a result, food safety will be a tremendous threat to the contaminated countries or regions. So, it is an important work to strengthen the food nuclear radioactive detection in those contaminated areas, and the detections help to ensure personnel health, maintain social stability and prevent panic buying or panic migration.To solve the problems talked above, this paper is based on existing researches and relying on Special Program of Major Instruments of China′s Minister of Technology, focuses on the detection of γ radioactivity in contaminated food after nuclear and radiation emergency happened. On the basis of researches on the measurement of γ spectrum and calculation of γ activity, this paper designed the portable detection systems of radioactive activity in food. The main contents and results as following:1) In combination of the principle of γ spectroscopy measurement, in-depth study of key technologies such as γ ray detection, nuclear signal acquisition, spectroscopy forming, spectrum transmission, spectrum analysis, energy and efficiency calibration, activity calculation, etc. An integrated design was proposed and detection systems of food radioactive contamination was designed.2) The γ-ray spectroscopy hardware circuit was designed, Na I(Tl) detector with high detection efficiency and good energy resolution was chosen to detect γ rays from the contaminated food. Nuclear signal was amplified via the preamplifier, modulated via conditioning circuit signal conditioning, amplified via programmable amplifier and filtered via anti-aliasing filter, then sampled via the high-speed ADC. The XILINX Spartan 3E series FPGA was used as main control chip while SPI bus way was used for communication to complete the nuclear signal’s acquisition and transmission. Where in the internal circuitry of the FPGA was developed, signal acquisition circuit, digital pulse peak detection circuit, spectrum shaping circuit, SPI control circuit and communication control circuit were designed, and the nuclear signal processing was achieved.3) The γ radioactivity measurement hardware circuit and software were designed. STM32F103VCT6 whose core was ARM Cortex-M3 was chosen as the master chip. The core of ARM Cortex-M3 is designed for embedded application which required chip for high performance and low cost, low power consumption. Communication protocol between STM32 and FPGA was made and the communication between STM32 and FPGA and the real-time transmission of spectral data was realized. PC read spectrum data from the STM32 via a serial port, and then wrote energy calibration value and efficiency calibration value to the STM32. The spectrum data from FPGA was smoothed by smoothing module, was extracted peak and found frontier of peak. This paper could identify nuclide and measure net peak area and radioactivity, then displayed radioactivity on TFT240320 LCD panel.4) System test. To verify whether all levels of analog circuits worked normally, the signal, by all levels of signal disposal circuit, such as the preamplifier and main amplifier and programmable amplifier circuit, was tested. With real-time display nuclear pulse signal of ADC acquisition, the peak value of pulse peak discriminator module and spectroscopy data of spectrum shaping module by ChipScopePro logic analyzer, the pulse peak identify module output of the peak value of pulse signal, the energy spectrum shaping module spectrum data. The stability of the internal FPGA hardware circuit was ensured. Spectrum data read from the FPGA was displayed on LCD to ensure the normal work of the communication module. Based on these, the measure of Cs-137 radiation sources was carried out, implying that the system can be used for nuclear emergency rapid detection of food contamination.This paper focused on the development of hardware and software, which was used in the food radioactive contamination fast detection. With constantly innovation in the design and development, the development of nuclear emergency food radioactive contamination detection systems was completed. Performance testing and preliminary experiments showed that each index of this system has reached the expected design goal.