Wire mesh capped DRPS based bronchial dosimeter for personal inhalation dosimetry due to radon progeny

A study has been carried out to experimentally determine the calibration factor (CF) of the passive bronchial dosimeter, which consists of a direct radon progeny sensor capped with a 100-wire mesh. First, the CF was determined in controlled environmental conditions simulated in a calibration chamber. With aerosol concentrations varying from 10⁴p cm^-3to 10⁵p cm^-3and relative humidity varying from 60% to 80% in the chamber, CF was observed to be nearly constant with an average value of (3.8 ± 0.5) × 10^-3mSv tracks^-1cm². Then, the CF was determined in real indoor environments in which it was again observed to be almost constant and the mean value was found to be (5.6 ± 0.1) × 10^-3mSv tracks^-1cm². Pooling all the data on CFs obtained under controlled conditions and in real indoor environments, a lognormal distribution of the CF was observed with a geometric mean and geometric standard deviation of 0.0052 mSv tracks^-1cm²and 1.28 respectively. The experimentally determined value of CF was found to be in close agreement with the theoretically estimated value, taking into consideration the unattached fraction of radon progeny. This dosimeter is passive, cheap, lightweight and, moreover, the CF being stable against environmental variations, will be useful in monitoring inhalation doses due to radon progeny for occupational workers.

Investigation of 220Rn emanation and exhalation from soil samples of Larsemann Hills region, Antarctica

In the present study, thoron exhalation flux density were measured in the soil samples collected around the Indian station namely Bharati (69° 24.41' S, 76° 11.72' E) and its nearby islands in the Larsemann hills region of Antarctica. Further, dependency of thoron mass emanation rate and emanation coefficient on the soil grain size was studied by segregating the soil samples into four different grain size groups: 50-100 μm, 100-200 μm, 200-500 μm and 500-1000 μm which showed that both of them follow a decreasing trend with increase in grain size. A comparison of measured mass emanation rate between different soil samples showed that it had a larger variation for the smaller grain size which eventually decreased as grain size increased while emanation coefficient was observed to be nearly constant for all the grain size groups. The variation in emanation coefficient with respect to mean grain size has been investigated and an empirical exponential model has been proposed for predicting emanation coefficient for different grain sizes.

Inhalation exposures due to radon and thoron ((222)Rn and (220)Rn): Do they differ in high and normal background radiation areas in India?

In India, High Background Radiation Areas (HBRAs) due to enhanced levels of naturally occurring radionuclides in soil (thorium and, to a lesser extent, uranium), are located along some parts of the coastal tracts viz. the coastal belt of Kerala, Tamilnadu and Odisha. It is conjectured that these deposits will result in higher emissions of radon isotopes ((222)Rn and (220)Rn) and their daughter products as compared to Normal Background Radiation Areas (NBRAs). While the annual external dose rates contributed by gamma radiations in these areas are about 5-10 times higher, the extent of increase in the inhalation dose rates attributable to (222)Rn and (220)Rn and their decay products is not well quantified. Towards this, systematic indoor surveys were conducted wherein simultaneous measurements of time integrated (222)Rn and (220)Rn gas and their decay product concentrations was carried out in around 800 houses in the HBRAs of Kerala and Odisha to estimate the inhalation doses. All gas measurements were carried out using pin-hole cup dosimeters while the progeny measurements were with samplers and systems based on the Direct radon/thoron Progeny sensors (DRPS/DTPS). To corroborate these passive measurements of decay products concentrations, active sampling was also carried out in a few houses. The results of the surveys provide a strong evidence to conclude that the inhalation doses due to (222)Rn and (220)Rn gas and their decay products in these HBRAs are in the same range as observed in the NBRAs in India.

"Deposition-flux to lung dose"--a new approach in radon inhalation dosimetry using wire-mesh capped direct radon progeny sensor

Assigning indoor radon doses to populations based on the widely used, cumulative radon concentration monitoring techniques is beset with errors arising due to uncertain equilibrium factors and unattached fractions. Moreover, the dose conversion factor (DCF) of radon decay products may vary by a factor of ∼40 within the particle size range from ∼0.5 nm to tens of micrometers. An ideal detector should have a response, which closely mimics the strong dependence of the DCF on the particle size. In this context, we propose a new approach in which the doses are computed directly from the time integrated progeny deposition fluxes on a suitably tailored surrogate surface. The deposition on this wire-mesh capped detector system closely mimics the deposition rate in human respiratory tract. The detection unit consists of an optimally designed wire-mesh capped Direct Radon Progeny Sensor (DRPS) system. Of the different wire-mesh types, 100 mesh types were found to be suitable considering the fine and coarse fraction penetration efficiencies. The calibration factor was theoretically derived as 0.0077 {mSv (Tracks cm(-2))(-1)}, for converting the measured atom flux in the 100-mesh capped DRPS system to inhalation dose attributed to radon progeny.

Results from time integrated measurements of indoor radon, thoron and their decay product concentrations in schools in the Republic of Macedonia

As part of a survey on concentrations of radon, thoron and their decay products in different indoor environments of the Balkan region involving international collaboration, measurements were performed in 43 schools from 5 municipalities of the Republic of Macedonia. The time-integrated radon and thoron gas concentrations (CRn and CTn) were measured by CR-39 (placed in chambers with different diffusion barriers), whereas the equilibrium equivalent radon and thoron concentrations (EERC and EETC) were measured using direct radon-thoron progeny sensors consisting of LR-115 nuclear track detectors. The detectors were deployed at a distance of at least 0.5 m from the walls as well as far away from the windows and doors in order to obtain more representative samples of air from the breathing zone; detectors were exposed over a 3-month period (March-May 2012). The geometric mean (GM) values [and geometric standard deviations (GSDs)] of CRn, CTn, EERC and EETC were 76 (1.7), 12 (2.3), 27 (1.4) and 0.75 Bq m(-3) (2.5), respectively. The equilibrium factors between radon and its decay products (FRn) and thoron and its decay products (FTn (>0.5 m)) were evaluated: FRn ranged between 0.10 and 0.84 and FTn (>0.5 m) ranged between 0.003 and 0.998 with GMs (and GSDs) equal to 0.36 (1.7) and 0.07 (3.4), respectively.