Relevance of radon progeny measurements for the assessment of inhalation doses in groundwater utilities.

The high radon concentrations measured in the indoor air of groundwater facilities and the prevalence of the problem have been known for several years. Unlike in other workplaces, in groundwater plants, radon is released into the air from the water treatment processes. During the measurements of this study, the average radon concentrations varied from 500 to 8800 Bq m-3. In addition, the indoor air of the treatment plants is filtered and there are no significant internal aerosol sources. However, only a few published studies on groundwater plants have investigated the properties of the radon progeny aerosol, such as the equilibrium factor (F) or the size distribution of the aerosol, which are important for assessing the dose received by workers. Moreover, the International Commission on Radiological Protection has not provided generic aerosol parameter values for dose assessment in groundwater treatment facilities. In this study, radon and radon progeny measurements were carried out at three groundwater plants. The results indicate surprisingly high unattached fractions (fp= 0.27-0.58), suggesting a low aerosol concentration in indoor air. The correspondingFvalues were 0.09-0.42, well below those measured in previous studies. Based on a comparison of the effective dose rate calculations, either the determination of thefpor, with certain limitations, the measurement of radon is recommended. Dose rate calculation based on the potential alpha energy concentration alone proved unreliable.

Assessment of radon, thoron, and their progeny concentrations in the dwellings of Shivalik hills of Jammu and Kashmir, India.

The present work determines the contents of active and passive indoor 222Rn, 220Rn, and their daughter in the 32 houses of the Reasi district of J&K, India. The passive 222Rn and 220Rn concentration was measured by dosimeters, whereas the active content was measured by active radon monitor. Progeny sensors and integrated samplers were operated for the evaluation of passive and active daughter contents of 222Rn and 220Rn. The measured averaged values of indoor 220Rn and 222Rn were 73 ± 40 and 22 ± 8 Bqm-3, respectively. The radon and thoron equilibrium factor has varied from 0.3 to 1.7 and from 0.006 to 0.6. The fine fraction of the above-mentioned gases was also calculated. The results of Mann-Whitney test statistically demonstrated significant differences between the content of indoor 222Rn, 220Rn, and their daughter for different seasons. The values of 222Rn, 220Rn, and their daughter content were appeared to be elevated in set of mud houses among all sets of houses. The values of all daughter concentration and indoor 222Rn were appeared to lie within the limit proposed by various agencies. The total doses were detected less than range commended by ICRP that suggested the district is safe as a health hazard point of view.

Attached, unattached fraction of progeny concentrations and equilibrium factor for dose assessments from (222)Rn and (220)Rn.

In this study, measurements of indoor radon ((222)Rn), thoron ((220)Rn) and their equilibrium equivalent concentration (EEC) were carried out in 96 dwellings from 22 different villages situated in Hamirpur district, Himachal Pradesh, India, by using LR-115 type II-based pinhole twin cup dosimeters and deposition-based progeny sensors (DRPS/DTPS). The annual average indoor (222)Rn and (220)Rn concentrations observed in these dwellings were 63.82 and 89.59 Bq/m(3), respectively, while the average EEC (attached + unattached) for (222)Rn and (220)Rn was 29.28 and 2.74 Bq/m(3). For (222)Rn (f Rn) and (220)Rn (f Tn), the average values of unattached fraction were 0.11 and 0.09, respectively. The equilibrium factors for radon (F Rn) and thoron (F Tn) varied from 0.12 to 0.77 with an average of 0.50, and from 0.01 to 0.34 with an average of 0.05, respectively. The annual inhalation dose due to mouth and nasal breathing was calculated using dose conversion factors and unattached fractions. The indoor annual effective doses for (222)Rn (AEDR) and (220)Rn (AEDT) were found to be 1.92 and 0.83 mSv a(-1), respectively. The values of (222)Rn/(220)Rn concentrations and annual effective doses obtained in the present study are within the safe limits as recommended by the International Commission on Radiological Protection for indoor dwelling exposure conditions.

Influence of Dose Conversions, Equilibrium Factors, and Unattached Fractions on Radon Risk Assessment in Operating and Show Underground Mines.

This paper compares the results of measurements taken in the underground workings of active and tourist mines. In these facilities, the aerosol size distributions of ambient aerosols at key workplaces and the distributions of radioactive aerosols containing radon decay products were determined. Based on these studies, dose conversions used for dose assessment and unattached fractions were determined. In addition, radon activity concentrations and potential alpha energy concentrations of short-lived progeny were also measured in the mines to determine the equilibrium factor. The dose conversions varied between 2-7 mSv/(mJ × h × m-3). The unattached fraction measured in active coal mines ranged from 0.01-0.23, in tourist mines from 0.09-0.44, and in the tourist cave it was 0.43. The results showed significant discrepancies between the effective doses determined from current recommendations and legal regulations and those determined from direct measurements of parameters affecting exposure.

Regulation and control methods for the unattached fraction of 220Rn progeny in a 220Rn progeny chamber.

The unattached fraction of 220Rn progeny is one of the key parameters in lung dose evaluation models. To study the behavior of unattached 220Rn progeny and to prepare for calibration of the unattached 220Rn progeny monitors, a 220Rn progeny chamber that could stably regulate different unattached fractions of 220Rn progeny was established. A recirculation loop to eliminate the effects of the sampling and a loop connected to the dilution chamber to supplement the carrier aerosol were set up. Also, a theoretical model regarding the regulation of the unattached fraction of 220Rn progeny was established. Continuous measurements of the unattached fraction were conducted using the combination of a single-layer wire screen and a filter membrane. The experimental results showed that, under different aerosol levels, the relative standard deviation (RSD) of 212Pb concentration during the continuous samplings was within 10.7% and the RSD of the unattached fraction of 212Pb was within 9.9%. The relative deviation between the theoretical and the experimental values of 212Pb concentration was within 16.7% and the model calculation values of the unattached fraction of 212Pb were consistent with measured results.

Estimation of unattached and aerosol-attached activities of airborne short-lived radon progeny in indoor environments.

Inhalation of the airborne short-lived radon progeny is regarded as the most crucial way of internal exposure to the natural radiation dose delivered to the human lung. In this respect, this study aims to determine the unattached and aerosol-attached activities of radon progeny and to estimate some important physical parameters employed to assess the radiological impact of this radiation on humans. For this purpose, radioactive aerosol samples collected on polycarbonate membrane filters to measure total alpha activity by passive alpha dosimetric technique using CR-39 detectors in sixteen different locations including some houses and workplaces in El Jadida city, in Morocco. In addition, the room-specific parameters and aerosol physical processes that affect the unattached and attached activity concentrations were determined. The obtained experimental results by the three-count method and room model parameters were used as input data on a developed PC-based software that we have developed to solve mathematical equations and calculate required physical quantities. Accordingly, the individual activities of radon progeny namely 218Po, 214Pb, and 214Po as well as radon activity concentration were determined. Simultaneously, the unattached and aerosol-attached activity concentrations (Cju and Cja) of radon progeny were calculated based on the room model calculation. Consequently, some radiological quantities used in the calculation of the lung dose were estimated. The results showed that the indoor radon activity concentration in different targeted locations ranges between 38 and 143 Bq. m-3 with an average value of 84.8 ± 9.5 Bq. m-3. The average obtained values of the equilibrium-equivalent concentration (Ceq), unattached fraction (fp), and equilibrium factor (F) at low and good ventilation rates change respectively from (24 Bq. m-3, 0.08, and 0.25) to (34 Bq. m-3, 0.02, and 0.41). Under normal environmental conditions, the average obtained values of Ceq, fp, and F, in houses and at workplaces were (17 Bq. m-3, 0.07, and 0.25) and (32 Bq. m-3, 0.04, and 0.35) respectively. Depending on the different aerosol conditions and obtained values of unattached fraction fp, the calculated average values of dose conversion factors (DCFs) were 8.70 mSv.WLM-1 and 11 mSv.WLM-1 in houses and workplaces respectively. These values were in good agreement with the recommended values by ICRP, which are in the order of 9 mSv.WLM-1 and 12 mSv.WLM-1 for houses and workplaces respectively.

Anomalously high unattached fraction of 220Rn decay products in the atmosphere of monazite storage facility.

High levels of the unattached 212Pb fraction of the 220Rn decay products in the atmosphere of the monazite storage facility were found: f1 = 0.3-0.5 at the aerosol concentration of 20 000 cm-3 and 0.1-0.16 at aerosol concentration ∼140 000 cm-3. It is shown that the sampling of aerosols in an atmosphere with a high concentration of thoron result in the local change of the equilibrium between the attached and unattached fractions near the sampling point. As a result, the measured value of the unattached fraction of thoron decay products may differ by several orders of magnitude from the mean value of unattached fraction the in the indoor atmosphere. A local increase of the unattached fraction 212Pb can take place in the worker's breathing zone in the atmosphere with a high concentration of thoron and it should be taken into account in the assessment of the inhalation intake of the thoron decay products for workers.

Assessment of progeny concentrations of 222Rn/220Rn and their related doses using deposition-based direct progeny sensors.

Indoor radon and thoron concentrations in the domestic environment result in natural radiation exposure to the public due to the inhalation of their short-lived decay products. Keeping this in view, the annual effective dose and other radiation risks due to radon/thoron progenies have been calculated. In this study, newly developed time deposition-based progeny sensors (DTPS/DRPS) were used for long-term passive determination of progeny concentrations in the environment of Jammu and Kashmir, Himalayas, India. The total equilibrium equivalent radon (EECRA + U) and thoron (EECTA + U) concentrations ("A" and "U" referring to attached and unattached fractions) were found to vary from 5 to 38 Bq m-3 with an average value of 18 Bq m-3 and from 0.48 to 5.49 Bq m-3 with an average value of 1.69 Bq m-3, respectively. The aerosol concentration, equilibrium factors, and unattached fractions for radon and thoron progeny have been estimated in normal living conditions and their dependence on each others have also been studied. The annual equilibrium factor for radon and thoron progeny has been determined from the calculated data. The estimated annual effective dose due to radon progeny (0.34 to 2.42 mSv y-1) and thoron progeny (0.13 to 1.54 mSv y-1) is found to be below the world's recommended level. Based on measurements of mean values of the unattached fraction, dose conversion factors (DCFs) in units of mSv per working level month (WLM) has been calculated and the average calculated values of DCFs are 24, 10, and 13 mSv WLM-1. The variability of equilibrium factor and radon/thoron progeny with different seasons, ventilation conditions, and types of houses were also analyzed.

Seasonal variability of equilibrium factor and unattached fractions of radon and thoron in different regions of Punjab, India.

A survey was conducted to estimate equilibrium factor and unattached fractions of radon and thoron in different regions of Punjab state, India. Pin hole based twin cup dosimeters and direct progeny sensor techniques have been utilized for estimation of concentration level of radon, thoron and their progenies. Equilibrium factor calculated from radon, thoron and their progenies concentration has been found to vary from 0.15 to 0.80 and 0.008 to 0.101 with an average value of 0.44 and 0.036 for radon and thoron respectively. Equilibrium factor for radon has found to be highest in winter season and lowest in summer season whereas for thoron highest value is observed in winter and rainy season and lowest in summer. Unattached fractions of radon and thoron have been found to vary from 0.022 to 0.205 and 0.013 to 0.212 with an average value of 0.099 and 0.071 respectively. Unattached fractions have found to be highest in winter season and lowest in rainy and summer season.

Effect of indoor activity size distribution of (222)Rn progeny in-depth dose estimation.

In this work, the attached and unattached activity size distribution of (222)Rn progeny ((214)Bi and (218)Po) were measured indoor. The fraction of attached progeny was collected using a low-pressure Berner cascade-impactor technique. A constructed wire screen diffusion battery was used for collecting the fraction of unattached progeny. Most of the attached activities for (214)Bi progeny were associated with the aerosol particles of the accumulation mode. The active median aerodynamic diameter (AMAD) of this mode for (214)Bi was determined to be 350nm with a geometric standard division (GSD) of 3. The GSD of unattached size distributions for (218)Po was 1.3 with an active median aerodynamic diameter (AMTD) of 1.3nm. Given that dose estimation is sensitive to environmental conditions, an analytical method was introduced to compute the local energy deposition of (218)Po alpha particles in a target volume of 1µm spheres located at different depths in bronchial epithelium. While the depth-dose distributions for nuclides uniformly distributed within the epithelium were found to be practically constant with depth, they decreased in an almost linear fashion with increasing depth for nuclides on the airway surface.

Estimation of EEC, unattached fraction and equilibrium factor for the assessment of radiological dose using pin-hole cup dosimeters and deposition based progeny sensors.

High concentration of radon ((222)Rn), thoron ((220)Rn) and their decay products in environment may increase the risk of radiological exposure to the mankind. The (222)Rn, (220)Rn concentration and their separate attached and unattached progeny concentration in units of EEC have been measured in the dwellings of Muktsar and Mansa districts of Punjab (India), using Pin-hole cup dosimeters and deposition based progeny sensors (DTPS/DRPS). The indoor (222)Rn and (220)Rn concentration was found to vary from 21 Bqm(-3) to 94 Bqm(-3) and 17 Bqm(-3) to 125 Bqm(-3). The average EEC (attached + unattached) of (222)Rn and (220)Rn was 25 Bqm(-3) and 1.8 Bqm(-3). The equilibrium factor for (222)Rn and (220)Rn in studied area was 0.47 ± 0.13 and 0.05 ± 0.03. The equilibrium factor and unattached fraction of (222)Rn and (220)Rn has been calculated separately. Dose conversion factors (DCFs) of different models have been calculated from unattached fraction for the estimation of annual effective dose in the studied area. From the experimental data a correlation relationship has been observed between unattached fraction (f(p)(Rn)) and equilibrium factor (F(Rn)). The present work also aims to evaluate an accurate expression among available expression in literature for the estimation of f(p)(Rn).