| As one of the main sources of natural radioactive exposures, radon is a kind of gas with strong migration capability and natural radioactivity. Besides, as the second factor which causes lung cancer(the first is smoking), International Commission on Radiological Protection(ICRP) approved the No. 126 publication Radiological Protection of Radon Exposure in April, 2014. The document points out: the commission strongly suggests that national regulatory authorities offer a national reference of radon concentration, which should be comprehensively based on the factors like current economic and social situations, and make it as low as 100 to 300Bq·m-3, which is reasonable. Radon precipitation refers to the movement that radon moves in the holes or cracks of media and the movement towards the external space through the surfaces of the media. The radon exhalation rate refers to the radioactive concentration of radon educed from the surfaces of soil or other materials in a given time and area. The measurement of radon exhalation is the key to finding source items in radon pollution control of the environment. The No.333 science books Measurement and Calculation of Radon Exhalation Rate of Uranium Tailing published by International Atomic Energy Agency(IAEA) have given some standards technically, but there are still many complex questions, and the calibration method has not been found yet.On the basis of the standard facilities of radon exhalation rate made by University of South China, the project focuses on the advanced radiometric techniques of the world, trying to figure out a new method and a standard facility for the measurement of radon exhalation rate. In addition, it is also helpful to offer technology base of the scale(or calibration) and measurement of radon exhalation rate measuring instruments, so as to ensure the quality of the field measurement of radon exhalation rate in scientific researches of China.Active carbon absorption and electrostatic collection are the common methods to measure the exhalation rate of radon. The former is often suitable for the measurements under the condition that humidity and temperature are relatively stable and radon exhalation rate changes slightly, while the latter is often used for a quick measurement. However, at present only after data modification, the method electrostatic collective radon measuring instruments(such as RAD7) can be used to obtain the result. In order to get a reliable and correct measuring result, it is needed to select the best method, which is to choose electrostatic collection to collect α spectroscopy as a reference to determine the value of radon exhalation rate. By doing so, not only can a fast and continuous measurement of radon exhalation rate be achieved, but also a standard value determining facility is made based on the method. Apart from this, studies on standardization, including the regulation on the operation of the standard method of radon exhalation rate and the technical standards about the scale(or calibration), are also made.In order to meet the various requirements of different measurements of rapid value determination facilities, to study and establish a method to determine the scale factors rapidly is needed. At first, the scale factors whose measurement period is 60 minutes by experiments are acquired. Then according to the inverse-proportional relationship between the scale factors of different measurement periods measured by the same instrument and α particle number decayed by 218 Po in the same measurement period, the rapid value determination of scale factors of the new device can be obtained.Besides, perfect the program of automatic correction on the humidity and temperature collected by electrostatic, and with the application of the rapid value determination device, the desiccant’s influence on radon exhalation of the surface of media in the radon chamber removes. And then study and apply α spectrum automatic regulation technology, making sure that the radon concentration measured by the rapid value determination device is correct and reliable under natural conditions. Also convert the method of least square to simulate the calculation of radon exhalation rate to algebraic operation. And the past phase in which computers are used to complete linear fit and process the data can be changed by the use of the built-in micro processor to give the result of the radon exhalation rate automatically, according to the radon concentration of the same measurement period.The facility offers a reference of radon exhalation rate for the calibration of radon exhalation rate measuring instruments. And in order to reasonably evaluate the uncertainty of the result of value determination of radon exhalation rate with standard facilities, the concept of uncertainty.e is brought in. And combining the theory of uncertainty, a model is made to analyze the theory to determine the values, analyzing the source of the uncertainty and evaluating the in accuracy of the combined standard. The results of determined values measured by the standard facility of radon exhalation rate in University of South China suggest: the inaccuracy rate between the determined values measured in 150 minutes by the standard facility whose radon exhalation rate is(0.39-2.62)Bq·m-2·s-1 and the relative combined standard is within 12%, which means a new method is available to evaluate the confidence level of the rapid value determination with standard facilities of radon exhalation rate.Develop applied researches using the standard method and facilities: absorb active carbon to collect γ spectrum to measure the radon exhalation rate of the soil and tailing and continuously collect α spectrum with electrostatic; figure out a reliable and standard measuring method to obtain the radon exhalation rate of the soil and tailing.The results show that the rapid value determination method of radon exhalation rate can realize a fast value determination of radon exhalation rate, and the continuous measurement makes field measurements of radon exhalation rate faster and more reliable, which is an important guarantee of radon evaluation and other areas like decommissioned uranium mine. |
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