Multi-parametric approach towards the assessment of radon and thoron progeny exposures

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.

The Analysis of 222Rn and 220Rn Natural Radioactivity for Local Hazard Estimation: The Case Study of Cerveteri (Central Italy)

Radon (²²²Rn) is the second most common cause of lung cancer after smoking. As radon poses a significant risk to human health, radon-affected areas should be identified to ensure people's awareness of risk and remediation. The primary goal of this research was to investigate the local natural radioactivity (in soils, groundwater, and indoors) because of the presence of tuff outcrops (from middle-lower Pleistocene volcanic activity) that naturally produce radioactive gas radon at Cerveteri (Rome, Central Italy). The results of the radon survey highlighted moderate (>16,000 Bq/m³) but localized anomalies in soils in correspondence with a funerary site pertaining to the Etruscan Necropolis of Cerveteri, which extends over a volcanic rock plateau. Indoor radon measurements were performed at several tuff-made dwellings, and the results showed medium-low (<200 Bq/m³) values of indoor radon except for some cases exceeding the reference level (>300 Bq/m³) recommended by the 2013/59 Euratom Directive. Although no clinical data exist regarding the health effects of thoron (²²⁰Rn) on humans, the study of ²²⁰Rn average activity concentration in the soil gas survey reveals new insights for the interpretation of radon sources that can affect dwellings, even taking into account the considerable difference in the half-lives of ²²²Rn and ²²⁰Rn.

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.

A novel method based on 220Rn (thoron) exhalation rate of indoor surfaces for robust estimates of 220Rn concentration and equilibrium factor to compute inhalation dose

The research into ²²⁰Rn (thoron) has generated an increasing interest in recent times due to the realisation of its radiological importance in many indoor environments. Though it is assumed that the contribution of ²²⁰Rn, per se, to the inhalation dose is negligible in comparison with that of its decay products, this may not be always true. Correct estimation of inhalation dose due to thoron requires a reliable method to measure the concentration of both ²²⁰Rn and its decay products in indoor air. However, due to its very short half-life (55.6 s) ²²⁰Rn shows large variation in its indoor activity concentration. This makes it difficult to have a robust value of ²²⁰Rn concentration which can be considered representative of a house, thus making the dose estimation unreliable. This issue has been addressed in the present study by developing a novel method that utilises the ²²⁰Rn exhalation rate from indoor surfaces as the basis for estimation of average ²²⁰Rn concentration in indoor air. The ²²⁰Rn concentration estimated in this manner can be converted to decay products concentration using a suitable equilibrium factor and finally the inhalation dose using appropriate dose conversion factors. A wall mounting accumulator setup has been developed for easy in-situ measurement of ²²⁰Rn exhalation from room surfaces. The method has been validated through comprehensive measurements in 25 dwellings in two different regions of India. The developed method is very good for large scale field surveys because of fast and easy applicability.

STUDY OF INDOOR RADON, THORON AND THEIR PROGENY IN SOUTH WEST KHASI HILLS DISTRICT OF MEGHALAYA, INDIA

A survey of indoor radon/thoron and their progeny concentrations was carried out in dwellings in the South West Khasi Hills district of Meghalaya, India. The survey was carried out using solid-state nuclear track detectors based on single-entry pinhole dosimeter and direct radon/thoron progeny sensors. The results are subjected to statistical analysis and discussed in the manuscript. The mean value of annual effective dose of the study region is estimated at 1.8 mSv.y -1. Seasonal variability and role of different indoor parameters are also discussed.

ASSESSMENT OF ANNUAL EFFECTIVE DOSE FROM EXPOSURE TO NATURAL RADIOACTIVITY SOURCES IN A CASE-CONTROL STUDY IN BIHOR COUNTY, ROMANIA

The purpose of the article is to evaluate the annual effective dose for 80 women divided into two samples; one sample located in the former uranium Băiţa-Ştei area, hereinafter referred to as case sample, respectively for a control sample, located in the same county, but exposed in most cases to indoor radon activity concentrations <300 Bq m-3. In this regard, the homemade 'RaThoGamma' kit was used, which contained two thermoluminescent dosimeters, a CR-39 track detector (RSKS) for indoor radon activity concentration, two CR-39 track detectors (Radtrak2®/ Radtrak2T®) for radon and thoron activity concentrations as well as Direct Radon Progeny Sensors/Direct Thoron Progeny Sensors for measuring time-averaged radon and thoron progenies concentrations. In addition, a total of 80 water samples were collected in order to evaluate the ingestion dose due to radon and radium activity concentrations in drinking water. The maximum total annual effective dose in the control sample was 14.1 mSv, while in the case sample the maximum annual effective dose was 60.5 mSv. This difference is mainly due to radon progenies inhalation. Other pathways did not show a statistically significant difference between the two samples, showing a minor contribution to the annual effective dose.

Quantification of an alpha flux based radiological dose from seasonal exposure to 222Rn, 220Rn and their different EEC species

This study summarizes the seasonal experimental data on the activity concentrations of indoor 222Rn (Radon), 220Rn (Thoron) and their progeny in Mansa and Muktsar districts of Punjab (India) using LR-115 solid state nuclear track detector based time integrated pin-hole cup dosimeters and deposition based progeny sensors for the assessment of radiological dose. The indoor 222Rn concentration was observed higher in the rainy and winter seasons while 220Rn concentration was observed higher in the winter season. However, Equilibrium Equivalent Concentrations (EECs) of 222Rn and 220Rn exhibited distinct seasonal behaviour unlike their parent nuclides. The average equilibrium factors for 222Rn (FRn) and 220Rn (FTn) were found 0.47 ± 0.1 and 0.05 ± 0.01, respectively. The annual arithmetic means of unattached fractions of 222Rn ([Formula: see text]) and 220Rn ([Formula: see text]) were found to be 0.09 ± 0.02 and 0.10 ± 0.02, respectively. The attachment rate (XRn) and attachment rate coefficients (β) of 222Rn progeny were also calculated to understand the proper behaviour of progeny species in the region. A new alpha flux based technique has been proposed and used for the assessment of absorbed dose rate and annual effective dose rate for radiation protection purpose.

CONTRIBUTION OF THORON AND PROGENY TOWARDS INHALATION DOSE IN A THORIUM ABUNDANT BEACH ENVIRONMENT

In an environment having thorium rich soil the activity concentration of thoron in soil gas and ground-level outside air is comparable to that to radon. Recent reports indicate that in terms of the energy of the alpha particle decays of thoron's progeny, its concentration in indoor air is significant, typically about half that due to radon progeny. We made a detailed radiometric profiling of inhalation dose to the population of the high background radiation area in the west southern coastal region of India. Here we report the results obtained from the long-term time integrated passive measurements of radon, thoron and their progeny concentrations in the high background radiation areas of Chavara and Neendakara hamlets of Kollam district. The equilibrium factors of radon and thoron with their progeny were determined for the region and was consistent with a previous study. The estimated value of total annual inhalation dose in the region ranged from 0.4 ± 0.06 to 3.7 ± 0.6 mSv y-1. The annual effective dose due to thoron and thoron progeny contributes ~35% to the total inhalation dose which means that thoron and its progeny is significant in assessing the radiation dose to the public.

Deposition and spatial variation of thoron decay products in a thoron experimental house using the Direct Thoron Progeny Sensors

Experiments have been carried out using the deposition-based Direct Thoron Progeny Sensors (DTPS) in a thoron experimental house. The objective was to study the thoron decay product characteristics such as the deposition velocities, spatial variability and dependence on aerosol particle concentrations. Since the deposition velocity is an important characteristic in the calibration of the DTPS, it is very important to study its dependence on aerosol concentration in a controlled environment. At low aerosol concentration (1500 particles/cm³) the mean effective deposition velocity was measured to be 0.159 ± 0.045 m h^-1; at high aerosol concentration (30 000 particles/cm³) it decreased to 0.079 ± 0.009 m h^-1. The deposition velocity for the attached fraction of the thoron decay products did not change with increasing aerosol concentration, showing measurement results of 0.048 ± 0.005 m h^-1 and 0.043 ± 0.014 m h^-1, respectively. At low particle concentration, the effective deposition velocity showed large scattering within the room at different distances from center. The attached fraction deposition velocity remained uniform at different distances from the wall. The measurements in the thoron experimental house can be used as a sensitivity test of the DTPS in an indoor environment with changing aerosol concentration. The uniform spatial distribution of thoron decay products was confirmed within the experimental house. This indicates that direct measurement of thoron decay product concentration should be carried out instead of inferring it from thoron gas concentration, which is very inhomogeneous within the experimental house.

Radon and thoron inhalation doses in dwellings with earthen architecture: Comparison of measurement methods

The radioactive noble gas radon (²²²Rn) and its decay products have been considered a health risk in the indoor environment for many years because of their contribution to the radiation dose of the lungs. The radioisotope thoron (²²⁰Rn) and its decay products came into focus of being a health risk only recently. The reason for this is its short half-life, so only building material can become a significant source for indoor thoron. In this study, dwellings with earthen architecture were investigated with different independent measurement techniques in order to determine appropriate methods for reliable dose assessment of the dwellers. While for radon dose assessment, radon gas measurement and the assumption of a common indoor equilibrium factor often are sufficient, thoron gas has proven to be an unreliable surrogate for a direct measurement of thoron decay products. Active/time-resolved but also passive/integrating measurements of the total concentration of thoron decay products demonstrated being precise and efficient methods for determining the exposure and inhalation dose from thoron and its decay products. Exhalation rate measurements are a useful method for a rough dose estimate only if the exhalation rate is homogeneous throughout the house. Before the construction of a building in-vitro exhalation rate measurements on the building material can yield information about the exposure that is to be expected. Determining the unattached fraction of radon decay products and even more of thoron decay products leads to only a slightly better precision; this confirms the relative unimportance of the unattached thoron decay products due to their low concentration. The results of this study thereby give advice on the proper measurement method in similar exposure situations.

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.

Estimation of attached and unattached progeny of 222Rn and 220Rn concentration using deposition based progeny sensors

The attached and unattached radon and thoron progeny concentrations have been calculated using deposition-based progeny sensors in Mansa, Muktsar, Bathinda and Faridkot districts of Punjab, India. The total (attached + unattached) equilibrium-equivalent (222)Rn concentration (EECRA + U) and total (attached + unattached) equilibrium-equivalent (220)Rn concentration (EECTA + U) were found to vary from 9 to 46 Bqm(-3) and 0.5 to 3.1 Bq m(-3), respectively. The concentrations of attached progeny nuclides for both (222)Rn and (220)Rn have been found to be greater than the unattached progeny nuclides in the dwellings of studied area. An attempt has also been made to assess the effective dose for (222)Rn and (220)Rn in the studied area. The radiation dose originated from (222)Rn and (220)Rn progeny is low and health risk is negligible.

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).

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.