| Radon is a radioactive gas arising from the decay of radium, which is a daughter of uranium and thoron.Inhalation of radon and its daughter products can cause lung cancer when they are present in enhanced levels. Radon is one of the most reasons of the four causes to lung cancer. It is widely believed that the greater the exposure to radon, the greater the risk of developing lung cancer. If a person who is receiving radon radiation has the smoking habit, it has more chance for him to suffer lung cancer.The air radon comes mainly from the underground soil and construction materials, and the underground soil and rock are the most source of radon. Radon is distributed over the earth's crust for over ten kilometers and moves up by diffusing and permeating. The underground building is the nearest way for radon to move up because it is in contact with the soil from all around or is built in mountain, and if the underground building has poor ventilation, it is easy for radon to accumulate to higher radon level.In our country, as the economy is developing and the population is expending, more and more under ground buildings are used to every places of producing and living. So more and more people are entering underground building working or living and they are receiving higher radiation.Using solid state nuclear detectors (SSNTD'S) , a survey of the air radon concentrations in 234 underground buildings was carried out during spring, summer and winter, respectively. The survey covered 23 cities include Beijing, Shanghai,Fuzhou, Quanzhou, Xiamen, Guangzhou, Shantou, Yangjiang, Wenzhou, Ningbo, Changsha, Guiynag, Guilin, Huhhot, Baotou, Jining, Erduos, Jinan, Qingdao, Nanchang, Shangrao, Zhengzhou,Wuhan.Totally 674 detectors were exposed in the survey and 601 of them were sent back to lab for obtaining radon concentration. Among these, there are 87 underground working places. The detectors were exposed in underground buildings for about three months before they were sent back. Measurements were carried out employing CR-39 detectors made in China, and the detector was calibrated and a density of 4.218 tracks *cm~2/ (KBq *m"3 *h ) was obtained for 222Rn. 74 sites were made duplicate measurements, account for 12% of total, and 90%of the variation coefficients were less than 20%. 43 detectors were measured for background, account for 7% of total. The measured limit was 8.654 Bq ? m"3 if the detectors were exposed for three month. For predicting the radon level of a certain city and studying the radon daily variation, Model 1027 continuous monitor from Sun Nuclear Corporation, U.S.A was chosen to measure the radon concentrations at some sites for over 24 hours.In the survey, the geological formation, coating level, decorating materials and ventilation condition of underground buildings were collected and analyzed according to their radon concentrations. Studied underground buildings were classified to four types in building style: saps, tunnels, basements and parking garages. After obtaining data, the radon concentration in different cities, underground building with different types and saps with different rock. The annual effective dose by, exposure to radon for people in underground working places was estimated. The seasonal radon variation in underground buildings with different construction type, as well as cities and sites with different use situation were analyzed. The main factors affecting the radon concentration in underground builds were pointed out. Some radon mitigation measures were suggested and a research for nearly a month on the reducing of radon level by ventilation in an underground space was carried out. In this paper, some conclusions were drawn below:(1) The survey covered 234 underground buildings, which included 109 in spring, 227 in summer and 193 in winter. The highest annual radon concentration(2482 Bq to"3) was detected at a site in Fuzhou, and the lowest one (14.9 Bq in"3) was found in a underground office in Yangjiang. The average annual radon concentration of all 234 underground buildings was 247 Bq ? m"3. Among the examined underground buildings, 171 underground buildings have annual radon concentrations below 200 Bq ? m"3, counting for 73% of the total sites;200 buildings have annual radon concentrations below 400 Bq ? m3, counting for 85% of the total sites;220 buildings have annual radon concentrations below 800 Bq ? m"3, counting for 94% of the total sites. With the equilibrium factor at 0.5, 15% of these buildings would have radon concentrations beyond the safe range for type I underground buildings, and 6% would be beyond that for type II underground buildings.(2) The radon concentrations are averaged according to city. In 11 cities in which radon concentrations were measured in spring, Fuzhou has the highest radon level and Yangjiang has the lowest radon level;In 22 cities in which radon concentrations were measured in summer, Fuzhou has the highest radon level and Shanghai has the lowest radon level;In 21 cities in which radon concentrations were measured in spring, Baotou has the highest radon level and Shanghai has the lowest radon level. For annual radon concentration, Fuzhou and Baotou have higher radon level while Shanghai and Guangzhou have lower radon level (ignoring Yangjiang because of its insufficient sites). Among 23 cities, there are 74% of total cities have radon concentrations below 200 Bq ? m"3, moreover, five cities including Guangzhou, Yangjiang, Quanzhou, Shanghai, Shangrao, which radon concentrations in underground buildings are below 100 Bq ? m\(3 ) That underground buildings in which there are people stay for over 8h in workday are called underground working places. 96.6% of underground working places have radon concentration within the limit of safe level set for controlling radon in dwellings in China.(4)Studied underground buildings were classified to four types in building style: saps, tunnels, basements and parking garages. Saps have the highest radon concentration. Parking garages have the lowest radon level.(5) saps built in mountain with different geological formation rock have different radon level. The sequence of rock in which radon concentration in saps from high to low is granite > tuff > quartz sandstone > limestone > andesitic porphyry o(6) There is some relation between radon concentration in underground buildings and that above ground in a city.(7 ) The radon concentrations in the underground buildings change through two cycle one day. The first cycle is from 12:00 to 0:00, and radon concentration in saps and tunnels start to rise and then to descend, and the highest value appears at about 19:00, while the radon variation in basements has opposite trend. The second cycle is from 0:00 to 12:00 and has a little change.(8) For different types of buildings, there is not a clear radon variation in garages, which is because of its characteristic and the way to use, while in saps, tunnels and basements, their radon concentrations in summer are higher than those in winter, and radon in spring are similar to annual radon level. Saps and tunnels have higher summer/winter ratio and it is larger in closed underground buildings than in unclosed underground buildings.(9) Comparing the radon seasonal variation in cities, it is found that there is little different of radon concentration in summer and winter in Zhengzhou. In Shangrao and Batou, radon in summer is lower than in winter. Except that, other 18 cities have higher radon in summer than in winter. In winter, the ratios of cities of radon concentration and annual radon are similar to each other, while in summer,the higher the average radon concentration of a city is, the higher its standard deviation is.(10) People working in underground working places in Fujian province receive the highest annual effective dose of 3.35 mSv by exposure to radon, and the lowest of 0.75 mSv in Shanghai. For all studied cities, people working in underground working places receive more annual dose than people working above ground. Fujian has the largest difference of annual dose received by people between working underground and above ground, while Guizhou has the little of that.It was estimated that there would be 2-3 person among 10000 persons die of lung cancer due to the lifetime fatality risk of 2.59 X 10~4 for people working in Fujian province.( 11 ) The geological formation, coating level, decorating materials and ventilation situation of underground buildings all affect its radon concentration.(12) A research on the reducing of radon level by ventilation in an underground space was carried, and theconclusions is that ventilation by air pump and air intake blower simultaneously is the most efficient method for radon reduction and ventilation for 8 hours will reduce radon by 91.4%.
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