Survey of 222Rn concentrations in the air of a tunnel located in Nagano City using the solid-state nuclear track detector method.

The survey of 222Rn concentration in the air of tunnels constructed during World War II has been performed using a solid-state nuclear track detector technique. For the practical application of this technique to the determination of 222Rn concentrations in air, some basic properties were experimentally examined on the cellulose nitrate film, Kodak LR 115 type II. The calibration coefficient of the cellulose nitrate film used is determined from a correlation between the 222Rn concentration in air and the observed number of perforated etched tracks for widespread radon concentrations. The slope of the linear relationship observed yields a calibration coefficient of (0.00209 +/- 0.00018) tracks cm(-2) (Bq m(-3) h)(-1). From the survey of 222Rn concentration in the air of tunnels, the concentration of several thousand Bq m(-3) was observed at the inner most area of the tunnel, and the seasonal variation was clearly observed. The exponential distribution of radon concentration as a function of distance from the openings of the tunnel suggests that the radon concentration in the tunnel is basically governed by diffusion and mixing of radon gas with air.     

222Rn detection efficiency and sensitivity coefficient of the LR 115-II nuclear track detector.

Radon activity concentrations in air were measured by the Kodak-Pathé LR 115-II nuclear track detector. Using the calibrated sensitivity coefficient of the detector (k = 0.0285 Bq-1 m3 tr cm-2 d-1 = 0.33 cm), the critical detection angle was calculated. In the alpha-particle energy region of 1-3.7 MeV, the detector efficiency for 241Am was near 32% but the 222Rn detector efficiency was 23%. The permeability constant of the detector paper filter was measured in a standard radon atmosphere and a value of 9.08 x 10(-6) cm2 s-1 was obtained.     

Indoor 222Rn measurements in the region of Beijing, People's Republic of China

Passive integrating activated C detectors were used to study the regional distribution and temporal variation of 222Rn in indoor air in dwellings in the Beijing region. Measurements were made in 537 dwellings, which were either detached houses or multi-family apartments. The city-wide study was completed in 1985. The distributions are approximately log-normal with 90% of the dwellings having 222Rn levels less than 60 Bq m-3. The weighted average 222Rn concentration has been found to be 22.4 Bq m-3. Averages for detached houses and multi-family dwellings are 25.9 and 15.2 Bq m-3, respectively. Assuming an equilibrium factor of 0.5 and an occupancy factor of 0.8, the average equilibrium equivalent concentration of 222Rn progeny is 11.2 Bq m-3 and the annual average effective dose equivalent is 1.1 mSv.     

室内氡的水平与控制措施

目的 验证北京市室内氡水平的分布,提出控制室内氡浓度若干途径。方法 以清华大学工程物理系室内环境质量评价中心测量的室内氡浓度数据与中国疾病预防与控制中心辐射防护核安全医学所、北京东城区卫生防疫站环卫科等单位在北京的测量数据相互印证,分析了北京市室内氡浓度的大致范围。结果 上述三家单位的氡浓度测量数据一致性比较好。结论 我国制定的"室内氡浓度行动水平"与发达国家制定的标准基本相同。在国家综合实力许可的情况下,应降低干预室内氡的行动水平,把氡致肺癌危险度降到最优化水平。加强通风、降低氡的析出率和建材控制等是室内氡的水平的有效控制措施。     

名古屋市室内空气222Rn、220Rn的测量及EECTn估算

目的 研究室内空气中^222Rn、^220Rn浓度以及室内平衡当量^220Rn浓度EECTn。方法 利用名古屋大学研制的新型被动累积式^222Rn、^220Rn测量杯在日本名古屋市进行了小规模的室内^222Rn、^220Rn的浓度调查，利用Deposition Rate Monitor估算了住宅室内EECTn。结果 在随机抽查的20个住宅室内^222Rn平均浓度为16．94Bqm^-3；其中5个住宅室内^220Rn平均浓度为58．09Bqm^-3，EEGTn平均值为2．75Bqm^-3。结论 本研究结果与日本全国性调查结果^222Rn浓度平均值15．5Bqm^-3相当。^220Rn的浓度在某些泥土墙壁的住房内可能达到比较高的浓度，进行进一步的研究是很有必要的。     

An instrument for measuring equilibrium-equivalent 222Rn and 220Rn concentrations with etched track detectors.

To simultaneously measure both 222Rn and 220Rn progeny concentrations, a new type of portable integrating monitor with allyl diglycol carbonate (CR-39) plastic detectors was developed. The monitor gives the average equilibrium-equivalent 222Rn and 220Rn concentrations (EEC(RN) and EEC(Tn)) during sampling intervals. The detection efficiencies of the alpha particles were calculated by Monte Carlo method. The lower limits of detection for EEC(Rn) and EEC(Tn) are estimated to be 0.57 Bq m(-3) and 0.07 Bq m(-3) for 24 h continuously sampling at a flow rate of 0.8 L min(-1). The measuring results with the new type monitors were confirmed through intercomparison experiments. In a small survey, a rather high 220Rn progeny concentration with an average of 1.73 Bq m(-3) was observed in traditional Japanese dwellings with soil/mud plastered walls. On the other hand, a very high 232Th concentration in soil was reported in China. They suggested that there is a possibility of high 220Rn progeny concentration in both Japan and China.     

Gamma distribution and house 222Rn measurements.

The statistical distribution of 222Rn measurements from basements and first floors of homes in northeastern Pennsylvania was investigated. The gamma distribution was statistically significantly superior to the normal distribution (p less than 0.005) in describing the frequency distribution of the logarithm of observed 222Rn levels. The fit to the data was closer both in the central portion and in the upper tail. The gamma distribution has certain characteristics that make it generally useful in the study of environmental toxic agents where several different exposures over a lifetime occur and must be combined, as for risk assessment or for statistical power calculations for epidemiologic studies.     

Monte Carlo calculations of LR115 detector response to 222Rn in the presence of 220Rn

The sensitivities (in m) of bare LR115 detectors and detectors in diffusion chambers to 222Rn and 220Rn chains are calculated by the Monte Carlo method. The partial sensitivities of bare detectors to the 222Rn chain are larger than those to the 220Rn chain, which is due to the higher energies of alpha particles in the 220Rn chain and the upper energy limit for detection for the LR115 detector. However, the total sensitivities are approximately equal because 220Rn is always in equilibrium with its first progeny, which is not the case for the 222Rn chain. The total sensitivity of bare LR115 detectors to 222Rn chain depends linearly on the equilibrium factor. The overestimation in 222Rn measurements with bare detectors caused by 220Rn in air can reach 10% in normal environmental conditions. An analytical relationship between the equilibrium factor and the ratio between track densities on the bare detector and the detector enclosed in chamber is given in the last part of the paper. This ratio is also affected by 220Rn, which can disturb the determination of the equilibrium factor.     

天津市部分新建楼房室内氡(222Rn)浓度水平调查

目的了解不同楼层对氡浓度的影响。方法在2002年以来对天津市部分新建楼房室内进行了验收性监测,一楼室内监测数据为130个,二楼及以上楼层室内监测数据128个。结果一楼室内平均氡浓度60.5Bq/m3,二楼及以上楼层室内平均氡浓度19.9Bq/m3,前者为后者3倍。结论楼层对氡浓度影响比较大,在今后的室内氡验收监测时,重点对一楼进行监测。