Research On The Key Technology Of Environmental Radiation Monitoring Instrument Calibration

At present,ionizing radiation has been widely used in medical,environmental,diagnostic,national defense,security,irradiation processing and other fields,creating great economic benefits for the country and has great application development prospects.The ensuing safety hazards caused by nuclear radiation are the top priority in the application of ionizing radiation.An important part of protecting the nuclear safety of the public and practitioners is how to effectively assess the exposure.The Institute of Ionizing Radiation of the Chinese Academy of Metrological Sciences,as a national-level measurement agency,has established 3 of the 4 recommended radiation qualities in the latest version of ISO 4037-1,and established it based on the environmental level X-ray standard laboratory?60?250?KV narrow spectrum series standard radiation quality.However,the existing conditions can no longer meet the requirements of extremely low natural radiation environment and extremely accurate verification.At present,the Chinese Academy of Metrological Sciences has not established a low-energy?10?40?k V narrow-spectrum series of radiation quality.In order to solve the problem of traceability of extremely accurate quantities of environmental monitoring instruments,the application of "X,?-ray measurement in extremely low background environment"The topic of "Key Technology Research" completed the design and processing of the low background box used in the Jinping underground laboratory in China,and the Monte Carlo method to simulate the shielding efficiency of the low background box.Work and environmental monitoring instrument verification work has been paved.This thesis firstly investigates the background source of natural radiation environment in Jinping underground laboratory,and designs it as lead?thickness 5cm?-copper?thickness 3cm?-stainless steel-plexiglass?thickness?based on theoretical calculation and Monte Carlo simulation method 3mm) as the main shielding structure,and a low-level box with a mechanical and physical structure designed according to the actual situation,such as universal wheels,sliding doors,and screws.Using the Monte Carlo simulation method,the shielding efficiency of the low floor box is higher than 90%,and the results are in line with expectations.Investigate the types and manufacturers of commonly used nuclear radiation detectors on the market,analyze the advantages and disadvantages of each product?ionization chamber,semiconductor detector and high-purity germanium detector?,and select the high-purity germanium detector as the most suitable for low background Environmental measurement instruments,the specific process is:On the low-energy X-ray reference optical machine of the Chinese Academy of Metrology,establish?10?40?kV narrow-spectrum series radiation quality,compared with the latest version of ISO 4037-1,additional filters,first half-value layer and second half-value The layer deviation is within±5%,the energy spectrum resolution deviation simulated by EGSnrc software is within 15%,the average energy is within 10%,the radiation field diameter is 55cm and the uniformity is greater than 95%.These measurement results are in line with international standards Claim.Relying on the above established?10?40?kV narrow-spectrum series radiation quality,the energy response of the GE high-pressure ionization chamber in the low energy section was measured.The results show that the lower the energy within the?10?40?kV range,the smaller the response factor The maximum value is 0.3 at 40kV,the detector is not suitable for low background environment measurement;The response function and angular response of the high-purity germanium detector BE2020 under the standard sources 241Am,60Co,and 137Cs of the Chinese Academy of Metrological Sciences were measured.The deviation of the incident angle to the count rate except ²⁴¹Am was less than 10%?E? From the calculation process,it can be concluded that the nuclear radiation detector that is more suitable for the Jinping underground laboratory is a high-purity germanium detector than the ionization chamber and the scintillator detector.On this basis,the MCNP software was used to establish the BE2020 model of the high-purity germanium detector,and the model was verified by experiments to analyze the characteristics of the internal radiation field of the low background box(taking ¹³⁷Co with an activity of 1Bq as an example),including particle fluence rate And the trend of change,the dose rate of standard points and the ratio of the number of scattered particles to the total number of particles.Finally,this paper also completed the design and experimental work of the FLUKE ionization chamber 50300A calibration device,and evaluated the uncertainty in the entire calibration,and the extended uncertainty calculation result was 5.764%.