The research of this project belongs to the field of metrology science and technology. In response to the gap in thorium and radon measurement and magnitude traceability technology in my country, systematic research on thorium and radon measurement technology and measurement standards has been carried out, and a series of technical results including measurement methods and devices has been obtained. The first thorium and radon measurement instrument testing device has filled the domestic gap, and the overall research results have reached the international advanced level.    

The radioactive gases radon (Rn-222) and thorium radon (Rn-220) and their daughters released by the natural radiation system of uranium and thorium in the atmospheric environment are inhaled into the human body and cause internal radiation. They pose the greatest threat to human health. They are one of the 19 major environmental carcinogens announced by the World Health Organization and the second largest cause of lung cancer and respiratory diseases. A report released by the United Nations Commission on the Effects of Atomic Radiation shows that the effective dose conversion coefficient of thorium radon daughters is more than four times that of radon daughters. The Th-232 content in my country's surface soil is significantly higher than the world average, 1.6 times that of the United States. The radiation hazard risk of thorium radon and its daughters to the public cannot be ignored. Thorium radon measurement is an indispensable task for environmental radioactivity monitoring and protection.  

my country's nuclear power construction has entered a period of rapid development. The environmental radiation background survey before the construction of nuclear power plants, the resource exploration of nuclear fuel uranium, the decommissioning of uranium mining and smelting enterprises and nuclear facilities and the control of environmental radiation pollution all require accurate Rn-220 and Rn-222 measurement data. Support.  

Due to the decay characteristics of the Th-232 system, it is difficult to form a radioactive balance. The half-life of Rn-220 and its daughters is very short. The decay in the sampling pipe affects the measurement results. The monitoring of thorium and radon in the environment is a typical weak radioactive measurement and is affected by radon. Interference, comprehensive factors lead to high technical difficulty and large measurement uncertainty (usually more than 30%), which is one of the main technical difficulties in the field of natural environmental radioactivity monitoring. Compared with mature radon measurement standards, there has been little research on thorium radon measurement in China, and measurement standards have been missing for a long time.  

This project originally and independently developed a built-in thorium emanation (Rn-220) source and an endogenous thorium emanation chamber, designed and manufactured a scintillation chamber detector thorium radon measurement system. Through theoretical research combined with experimental verification, the derivation, calculation methods and results of key parameters such as the detection efficiency and lower detection limit of pure Rn-220 and Rn-222/Rn-220 in a mixed environment are established, and the technical method of measuring thorium radon in a scintillation chamber flowing gas type thorium radon measurement is systematically discussed. The calculation, correction methods and results of the influence of gas path parameters such as sampling flow rate, sampling pipe volume and scintillation chamber volume on the measurement results are obtained, which has guiding significance and application value. The research results improve thorium radon measurement technology, establish a thorium radon volume activity measurement standard, and unify thorium radon measurement values.  The research results of the project have independent intellectual property rights, and the thorium emanation source production technology is the first in China. The temperature and humidity of the endogenous thorium emanation chamber and the volume activity of thorium and radon are stable and controllable, and the spatial distribution is uniform; the value of the detection device is compared with the original standard of the German Federal Institute of Physics Technology (PTB) Rn-220 volume activity, the relative deviation is only (0.2~2.5) %.  

The research results have become an important part of the natural environment radioactivity measurement value guarantee system, further improving my country's radioactivity measurement and calibration service capabilities, providing reliable measurement technical support for related fields, helping to maintain public radiation safety, protect the environment, and promote The technological advancement of nuclear detection instruments and serving the development of nuclear energy have achieved remarkable benefits.