The Design Of Activity Detector With Method Of Nuclear Energy Spectrum Measurement For Food

People pay more and more attention on food safety problem, radioactive detection of food is a important item. Radioactive contamination has a great deal of harm on hunman body and last for a long time.Through the food intake of radioactive material cause internal radiation to human body, the harm is more serious.Based on this point, the purpose of this paper is to design a activity detector for food in response to food testing requirements. Now in the market, the radiation detector, mostly be done with the method of nuclear pulse signal counting, and they have some soft spots.This article with the method of nuclear energy spectrum measurement to design the activity detector and good results are obtained.This article includes the following several parts: the design of the detector, the design of of signal amplifying unit, the design of module to get the data and process the data and the algorithm design of activity, etc, In the design of probe, by comparing the detection efficiency of various sensors, and this article select Nal (T1)(Φ50x50mm) as a probe of radionuclides. After that,this article analyzs the bias circuit of photomultiplier tube and the signal output circuit (preamplifier).Eventually completed the design of detector. The design of signal amplifying unit, mainly concentrated in the design of the amplifying circuit and the selection of amplifier,etc. Data acquisition module and high-speed, high-precision AD converter to realize the collection of signals, this paper selects the AD9237chip (12,20multisided platforms), and finally to meet the system requirements.After collecting signal, the signal has been developed from analog signals into digital signals, the signal processing is essentially for digital signal processing. Based on FPGA hardware platform,to complete the following parts:baseline deduction, pulse shape, pulse amplitude discriminator algorithm deducted from the proceeds.The baseline estimate of link based on the adaptive Kalman filtering algorithm, the algorithm is the classical Kalman filter algorithm thay has been improved and optimized,and good filtering effect was obtained. This article uses the method of the trapezoidal shape, through transform the input signals and output trapezoid signal to Z state, obtain the transfer function.Then convert the transfer function into the form of a specific formula, so that in the subsequent hardware programming work become simple intuitive.The method of trapezoidal shaping is beneficial to the improvement of the energy resolution of the system. Computer simulation is carried out for each algorithm in this paper. The concrete operation is realized by using MATLAB software.After digital processing, signal must be sended to the PC for operations, such as smooth, peak. Interface unit are introduced in detail in this paper, the unit is based on the hardware of MCU STC89C58RD+, use CP2102(USB to UART) communication hardware implementation. Main work were done by a single-chip microcomputer in the interface unit. And it it control some periphery auxiliary equipment system (dc motors, lights, etc.).This article introduces the instrument’s debugging work in detail, mainly including the photomultiplier tube high voltage,set the amplifier amplification, the setting of the main energy, calibration algorithm for the activity coefficient, etc.After testing, various performance of this instruments can meet the requirements (Japan standard), the energy resolution and measuring accuracy has better performance.It was able to adapt to the demand of the market, the instrument has been marketed in Japan as an fininshed product. Japan’s fukushima nuclear plant resulted in local radioactive pollution, this device adapted to the market demand, can serve for local residents very well.