[en] Diffusion coefficients of unattached radon progeny were measured with a graded screen array at the EML radon/aerosol chamber. The measurements were made under different environmental conditions. The particle concentration in the radon chamber was around <1 cm^-3 throughout the whole experiment. The temperature and the relative humidity were set at 20 deg. C, and 20, 40 and 75%, respectively. The influence of relative humidity on the diffusion coefficient was investigated, however only minor differences were found. Consequently, the average diffusion coefficient of unattached ²¹⁸Po was estimated to be 0.065 ± 0.010 cm².s^-1. (author)

[en] A preliminary survey was conducted to determine atmospheric radon and thoron concentrations, and soil gas radon concentrations in South Korea. The atmospheric radon and thoron measurements were made with a radon-thoron discriminative monitor and soil gas radon measurements with a hand-made radon monitor over a year. Six cities were chosen as the measurement site in South Korea. A polycarbonate film and a CR-39 detector were used as detectors for the radon-thoron discriminative monitor and the soil gas radon monitor, respectively. The detectors were replaced every 2-3 months during the survey period so as to observe seasonal variations of the concentration. From the limited data, the outdoor radon concentration has appeared to be somewhat higher than the typical value in the UNSCEAR report. The mean outdoor to indoor concentration ratio was estimated to be 0.6. Since high thoron concentrations were found in some areas, attention must be paid to thoron for accurate dose assessment. The soil gas radon concentration was observed in the range of 3.9-23.1 kBq.m^-3. (author)

[en] In vivo counting of ²¹⁴Pb was conducted to estimate the deposition and retention of radon progeny in the human respiratory tract. Two volunteer subjects were exposed to high radon concentrations. After the exposures, activity deposited in the extrathoracic (ET) region for each subject was measured using a NaI(Tl) detector. According to the International Commission on Radiological Protection (ICRP) model, a reference value for particle transport rate from ET₂ to the GI tract is 100 d^-1 (half-time, 10 min). The effective half-time of ²¹⁴Pb deposited in the ET region was calculated for pure nose and mouth breathers, using the ICRP reference transport rate. While the measured half-times for nose breathers were generally consistent with the calculated values, those for mouth breathers were significantly larger than the calculated values. The results indicated that the particle transport rate from ET₂ to the GI tract was much smaller than the reference value in the ICRP model. (author)

[en] The following problems on radon face us: establishment of the dose assessment, exposure due to thoron and technologically-enhanced exposure due to radon/thoron based on human activities. The radon problem has not yet been solved. When estimating dose, two different approaches are used for assessment. One is an epidemiological approach. In the epidemiological approach, the dose is derived from the relationship between the alpha exposure, i.e., the potential alpha energy concentration and the estimated excess relative risk for lung cancer among miners. The other is a dosimetric approach. The dose is derived from laboratory investigation in this case. There is a three-time difference between the two. It is obvious that information on the particle size of radon progeny is indispensable for accurate dose assessment. In order to combine the two estimates from the two approaches, both mine and home aerosols should be sufficiently characterized. As the second problem, recent studies have shown that attention must be paid to thoron because high thoron concentrations were occasionally observed in some areas. Although most of passive radon detectors are generally designed to minimize the entry of thoron, some of them were affected by the presence of thoron. It is important to understand the performance of the detector with an adequate thoron exposure facility before practical use. As the third problem, radon/thoron concentrations might be enhanced in a closed environment. In this circumstance, their concentrations should be mitigated with proper countermeasures. Building materials can be recognized as the their sources. Exhalation rates of radon and thoron from walls were measured in a traditional Japanese wooden house where a high thoron concentration was observed. No radon exhalation was detected but thoron exhalation rate was as high as that from soil. The dose due to thoron progeny cannot be ignored in such indoor environment. (author)

No abstract available

[en] An instrument performance test has been carried out for a radon measuring system made in Hungary. The system measures radon using the alpha-track detection technique. It consists of three parts: the passive detector, the etching unit and the evaluation unit. A CR-39 detector is used as the radiation detector. Alpha-track reading and data analysis are carried out after chemical etching. The following subjects were examined in the present study: (1) radon sensitivity, (2) performance of etching and evaluation processes and (3) thoron sensitivity. The radon sensitivity of 6.9x1^-4 mm^-2 (Bq m^-3 d)^-1 was acceptable for practical application. The thoron sensitivity was estimated to be as low as 3.3x10^-5 mm^-2 (Bq m^-3 d)^-1 from the experimental study. (author)

No abstract available

[en] A continuous ²²⁰Rn concentration monitor for an estimation of time variation has been developed. The monitor differentiates ²²⁰Rn from ²²²Rn using the spectroscopy method. In addition, it introduces the electrostatic collection method to elevate the collection efficiency of ²¹⁶Po. In order to maintain perfectly dry conditions with a water vapour concentration of 0.1 g.m^-3 in the collection and decay chamber, both a dehumidifying device and agents (Model DH-209, CaC1₂ and CaS0₄) are included. The preferred electrostatic collection voltage on the detector, S-3204-06, has been determined to be -6 kV using a chamber of 0.00152 m^-3 and the stability of the relative collection ratio of ²¹⁶Po has been experimentally verified under this condition. The sensitivity of the monitor is estimated as 1.60 counts per Bq.m^-3 hour. The corresponding lower detection limit of ²²⁰Rn with a relative statistical error of 50% is 2.5 Bq.m^-3 for a one hour measurement. Therefore the apparatus has sufficient sensitivity to estimate the time-varying ²²⁰Rn concentration at natural outdoor levels. (author)

[en] A series of measurements were carried out to understand the characteristics of radon and its progeny in air-conditioned office buildings. Long-term measurements of radon were made with etched track detectors. Continuous measurements of radon and its progeny concentrations were also conducted in some buildings to study their temporal variations. The results show that radon and its progeny concentrations routinely varied along with working activities. They are generally low while people are working, due to air conditioning, whereas they rise steadily after the air conditioning stops. When considering action levels not only in homes but also workplaces, attention should be paid to annual doses from the viewpoint of radiation protection. The annual dose is generally estimated with a long-term measurement of radon concentration using a passive device such as an etched track detector. Since its reading corresponds to a long-term average concentration regardless of working hours, the annual dose will be overestimated. When comparing a real dose after considering the working hours, they differ by a factor of more than 2. (author)

[en] The present paper summarizes the findings of studies carried out since 2014 in the uranium- and thorium bearing regions of Poli and Lolodorf, respectively, located in northern and southern Cameroon. It also underlines future prospects for strengthening the radiological protection of members of the public exposed to environmental natural radiation in Cameroon. In situ gamma spectrometry and car-borne surveys were performed in the above regions to determine activity concentrations of natural radionuclides in soil and air kerma rates to assess the effective external dose received by members of the public. High natural radiation areas were located and selected for indoor radon, thoron and thoron progeny measurements. Raduet detectors and thoron progeny monitors were deployed in 300 dwellings to measure radon, thoron and thoron progeny indoors in order to assess the inhalation dose received by members of the public. External effective dose ranges of 0.15-0.63 mSv/year with the average value of 0.4 mSv/year in the uranium bearing region of Poli and 0.1-2.2 mSv/year with the average value of 0.33 mSv/year in the uranium- and thorium bearing region of Lolodorf. The inhalation dose due to radon and thoron ranges, respectively, between 0.87-2.7 mSv/year and 0.08-1.0 mSv/year with average values of 1.55 mSv/year and 0.4 mSv/year for Poli, and between 0.6-3.7 mSv/year and 0.03-3.0 mSv/year with the average values of 1.84 mSv/year and 0.67 mSv/year for Lolodorf. Contribution of thoron to the total inhalation dose ranges around 3-34%, with an average value of 20.3% in the uranium region of Poli and 1-79% with the average value of 27% in the uranium- and thorium-bearing region of Lolodorf. Thus, thoron cannot be neglected in dose assessment in order to avoid biased results in radio-epidemiological studies. (author)