Development Of Low Background Tritium Concentration Measurement Instrument

There are many places related to occupational radiation of tritium in the nuclear industry system, in which the most typical is nuclear power station, whether the heavy water reactor or the light water reactor will produce a certain amount of tritium. Besides fission reactor, radioisotope production reactor, nuclear submarine power reactor, ongoing research nuclear fusion reactor and other nuclear facilities will also release the tritium to the environment. According to the "national nuclear power development project planning (2005-2020)", China's nuclear power will enter a period of rapid development in the coming years, and China participated in the International Thermonuclear Experimental Reactor (ITER) program in 2006 provides a good opportunities for the development of China's tritium related technology. Tritium monitoring and control, and tritium safety and environmental impact is becoming a special study areas.Tritium technology research and development carried out earlier abroad, Faltings and Harteck et al measured the concentration of tritium in heavy water samples using high sensitivity radioactive methods in 1952.Now foreign multinational companies such as Germany's BERTHOLD, AMETEK U.S. companies, France's Canberra developed environmental tritium contamination monitors with low background, wide range of automatic switching, automatic data recording, storage and other functions. But their instruments are generally more expensive. China began to develop monitoring of tritium since the late 70s of last century. Recent years, with the development of nuclear technology, domestic research institutions keep track of the progress monitoring of tritium abroad, improve the domestic tritium pollution monitoring instruments, and has achieved some results, such as: TAM series of air tritium monitor researched by the China Institute for Radiation Protection. However, compared with foreign instruments, these instruments are still lagging behind in the detection limit, accuracy and detection efficiency.Thus, this paper is joint sponsored by technology fundamental work in the Ministry of Science and Technology"RBF-based algorithm for low background radiation monitoring technology and equipment research (Gant No. 2008IM040500)"and "HB-01 gaseous tritium contamination concentration meter "project which cooperate with the China Academy of Engineering Physics. The development of the low background tritium concentration measurement instrument has been completed as follows:(1) Select the proportional counter and design vacuum deviceIn order to measure the concentration of tritium in the gas sample more accurately and reduce background interference, this paper selected a proportional counter and processed the inner of the proportional counter into sealed chamber. Furthermore we designed and processed vacuum equipment matching. The sealed chamber will be Vacuumed and filled with the sample gas and the P10 gas (90% argon +10% methane),and then we begin measuring. At the same time we can clean of the proportional counter to reduce the tritium memory effect in the high temperature.(2)To achieve the function of signal acquisition and processingThe preamplifier is following the detector, whose function is to amplify and convert the weak signals collected by the detector into pulse signals. In the design of preamplifier, low noise signal processing and filtering are the major concern issue.Signal acquisition and processing is mainly amplification the small signal which is from the preamplifier and then filtering, screening of the upper and lower threshold, over the peak detection, in between the upper and lower threshold signal AD conversion. Signal reasonable amplification, filtering and screening are the key to this part of the design. Data component is mainly transmitted the processed data to the PDA via Bluetooth.(3) Complete the software of spectrum data processing and display based on PDA This paper carry out spectral analysis method research and develop a real-time and efficient set of transmission, processing, display, storage as one of the control software, which realize data display and spectrum data processing and display. Spectrum data processing and display includes smoothing the original spectrum data and spectral display, energy calibration, peak drift correction, automatic peak search, peak area calculation, radionuclide identification and other functions. In this way we can locate and distributeβspectrum of the unknown radionuclide, and provide the basis for the channel width setting.The innovations are as followings:(1) This paper develops of a low background tritium concentration measuring instrument, which mainly measure the tritium decay product of low energyβ. It can meet measurement the low-gas samples collected, the detection limit is 1Bq/L, and the highest measured concentration is 4×10~4Bq/L.(2) This paper carries out tritium contamination measurement under high vacuum from the research and innovation radionuclide measurement.This paper selected a proportional counter and processed the inner of the proportional counter into sealed chamber. The sealed chamber will be Vacuumed and filled with the sample gas and the P10 gas (90% argon +10% methane),and then we begin measuring. In this way, it can significantly reducing the background interference and making detection background smaller than 6cpm.(3) The paper carries out spectrum analysis method research, and uses C++ language software in Visual Studio 2008 integrated development environment to develop a set of measuring software based on Windows Mobile 6.5 OS of PDA ,which has the ability of transmission, processing, real-time display and storage, can realize the data and spectrum displaying and processing. Spectrum processing and display mainly has functions of primitive spectrum smoothing processing, spectrum display, energy calibration, automatic peak-seeking, peak area calculating, and radionuclide identification.In summary, this paper spreads out tritium contamination measurement under high vacuum from the research radionuclide measurement, and the paper carries out spectral analysis method researching and developing a real-time and efficient set of transmission, processing, display, storage as one of the control software. The paper has developed a low background tritium concentration measurement instrument. After the system performance test, the charge sensitive preamplifier can get good Gaussian waveform, and the plateau of the proportional counter is about to 400V, extends from 2000V to 2400V, the plateau slope is about 0.6184%/100V. The system has good stability and low detection limit.