The Research And Development Of Directly Measured Radon In Balloon Method And Its Preliminary Application

This thesis topic is derived from the863plan resources environmental technology subject "high-precision spectrum instruments development"(project number:2012AA061803).Radon is a special kind of gas with inertia and radioactivity. Research on radon detection and migration of radon progeny has important significance on environmental protection, radiation protection, geological prospecting and earthquake prediction. Recently, radon and its daughters’harm and protection have caused widespread concern in the international radiation protection community. ICPR and some other international organizations have developed a serial of protection principles and provisions. Scholars of studies have shown that high concentrations of radon can cause lung cancer, and long-term living in the environment of low concentrations of radon will increase the risk of lung cancer. Epidemiological survey also shows a certain relationship between radon and lung cancer. Radon has become the second largest reason of causing lung cancer. Because of the cascade decay characteristic of radon, its measurement has been a difficult subject in the field of nuclear physics experimental methods.《Standard methods for radon measurement in environmental air)) have recommended a total of four methods:traces etching method, Activated charcoal method, Double-filter method and Balloon method. According to the measurement time, scholars put them into fast radon and slow radon measurement method. The first two are slow radon measurement method; the latter two are fast radon measurement method. According to the manner of collecting radon, scholars divided them into active and passive radon method, the first two of which are passive radon method, the latter two is active radon method; These four methods can accurately measure the concentration of radon, however, only balloon method is able to measure the radon concentration of environment and measure the concentration of radon progeny. This thesis develops directly measuring radon with balloon method based on Thomas absolute radon formula, which can measure the concentration without reaching radioactive equilibrium. The device integrates balloon sampling system and measuring system and designs extraction and exhaust circuit which implements the suction and exhaust half automation of radon measurement device and improves sampling system, basically overcoming the air leaking shortcoming of early balloon radon measurement device and improve radon measurement device overall stability and measurement results accuracy. The results achieved in this article are as follows:1) Because early balloon Radon meter sampling system and measuring system are independent of each other, when operating, it is to cause air leaking. Balloon method integrates balloon sampling system and measuring system and designs semi-automatic/exhaust sampling system:realize the transition of the two gas path and basically eliminate the air leaking through the control of two three-way valves.2) Based on the measuring mechanism of directly measuring radon with balloon method, establish mathematical models of sampling stage, waiting stage, exhausting stage and measuring stage; deduce calibration factor theoretical expression for directly measuring radon with balloon method. The theoretical calibration factor of directly measuring radon with balloon method is1.70; the calibration factor got in South China university radon room is1.92; the relative deviation is11.46%.3) U value test results of balloon radon measurement device eight hours long term stability show:The calculated value of U is0.62, which is less than the limit value Ua=1.96and show that the tested date during this period is in affirmative domain with good device stability. Under the same measuring condition, the contrast experiment between directly measuring radon with balloon method and Rad7emanometer shows:the radon distribution range tested through directly measuring radon with balloon method is10.20～86.7Bq/m3; while the result Rad7emanometer tested is10.40～88.7Bq/m3. Through directly measuring radon with balloon method the maximum value tested is86.7Bq/m3on16:55and the minimum value tested is44.2Bq/m3on1:59; while Through Rad7emanometer, the maximum value tested is88.7Bq/m3onl7:00and the minimum value tested is33.8Bq/m3on02:00. The concentration of radon tested through the two kinds of radon measuring devices under the same condition are coincided. The precision and accuracy of directly measuring radon with balloon method is very good and can be applied to practical measurement.4) By means of directly measuring radon with balloon method survey the level of radon consistence of the lab building and Underground source repository in geonomy nuclear technology laboratory. The measured results show that the average radon concentration in the experimental building is21.00±13.81Bq/m3,which is below the national housing radon concentration limits; the radon concentration of the different size of the rooms are not the same, the average of radon concentration the large room is11.36±4.54Bq/m3while the smaller room’average radon concentration27.43±14.28Bq/m3;The average radon concentration in the underground source repository is562.02±68.59Bq/m3,when working or experiment in the underground source repository, the measurement of protection and reducing radon must be adopted.