Unattached Progeny Research Articles

Measurement of Indoor Radon, Thoron and Their Attached and Unattached Progeny Concentrations in Dwellings of Gurugram, India

Estimation of indoor radon levels in the indoor air of a dwelling is an important aspect for the good health of human population spending a substantial portion of their lifetime indoor. Indoor radon combining with thoron and their progenies can accumulate in the houses to a value not suitable for the health of the people living there. The present paper is an attempt in this direction, to find the levels of the above-mentioned radioactive gases with their progenies in the dwellings of the Gurugram district of Haryana. The study was conducted in the summer season in 50 dwellings of the Gurugram district. International Commission on Radiological Protection (ICRP) guidelines were followed to evaluate the results obtained in the study and the district was found to be in the less hazardous zone due to presence of natural radioactive gases in indoor environment of dwellings.

Exposure to Radon and Progeny in a Tourist Cavern.

The primary objective of this work was to characterize employee exposure to radon and progeny while performing guide/interpretation and concessions duties in a tourist cavern. Radon gas and progeny concentrations, fraction of unattached progeny, and other environmental parameters were evaluated in a popular tourist cavern in Southeastern New Mexico. Alpha-track detectors were used to measure radon gas in several cavern locations during a 9-mo period. Additionally, radon gas and attached and unattached fractions of radon progeny were measured at three primary cavern work locations during a 1-d period using a SARAD EQF 3220. Radon gas concentrations in the cavern were elevated due to extremely low air exchange rates with substantial seasonal variation. Mean measured radon concentrations ranged from 970 to 2,600 Bq m-3 in the main cavern and from 5,400 to 6,000 Bq m-3 in a smaller cave associated with the regional cave system. Measurements of unattached fractions (0.40-0.60) were higher than those commonly found in mines and other workplaces, leading to the potential for relatively high worker dose. Although radon gas concentrations were below the Occupational Safety and Health Administration Permissible Exposure Limit, employees working in the cavern have the potential to accrue ionizing radiation dose in excess of the annual effective dose limit recommended by the National Council on Radiation Protection and Measurements due to a high unattached fraction of radon progeny. There was a strong negative correlation between unattached fractions and equilibrium factors, but these parameters should be further evaluated for seasonal variation. Introduction of engineering controls such as ventilation could damage the cavern environment, so administrative controls, such as time management, are preferred to reduce employee dose.

AN EXPERIMENTAL CHAMBER FOR TESTING ABATEMENT EFFECTS OF RADON EXPOSURE WITH DIFFERENT MEASURES.

For more effective testing the abatement effects of radon exposure with different counter measures, an air-conditioned laboratory room was reformed as an experimental chamber. Based on the well control and real time monitoring of concentrations of 222Rn, its attached and unattached progeny and their size distributions, the chamber could provide three modules corresponding to ventilation, source reduction and filtration for abating radon exposure. Preliminary results showed that the chamber was useful for testing the abatement effect of indoor radon exposure.

Dose assessment from the exposure to attached and unattached progeny of radon and thoron in indoor environment

The radiation dose from the exposure to radon (222Rn) and thoron (220Rn) is mainly contributed by their progeny, not by the gases themselves. This study aims to investigate the health risk associated with the internal exposure to attached and unattached progeny of 222Rn and 220Rn in the indoor environment of Garhwal Himalaya, India. For this purpose, the passive measurements of attached and unattached progeny levels of 222Rn and 220Rn were performed in Garhwal Himalaya, India using nuclear track detector based recently developed progeny sensors. The measured values of unattached and total progeny concentrations were used to estimate the unattached fractions and annual effective doses. The annual mean unattached fractions of 222Rn and 220Rn progeny were found to be 0.15 ± 0.04 and 0.17 ± 0.05, respectively. The estimated values of the annual effective doses were found to be 3.4 ± 1.9 mSv/y and 0.7 ± 0.4 mSv/y due to the progeny of 222Rn and 220Rn, respectively. The methodology and results obtained are discussed in details.

Comparative study of 222Rn/220Rn progeny concentration and estimation of age-dependent dose due to inhalation of radon progeny for different body organs

ABSTRACTIn the present study, the age-dependent doses due to inhalation of short lived decay progeny of radon, i.e., 214Po to different body organs have been calculated for the inhabitants of the Jammu district, Jammu & Kashmir, India. The estimated age-dependent doses for different body organs due to inhalation of radon progeny through air for all age groups varied between 0.002E-06 and 0.10 n Svy−1 which were found to be well within the recommended limit of 1000 µ Svy−1 (ICRP). The progeny concentration of radon and thoron was calculated and compared by two different techniques. The attached and un-attached progeny concentration of radon and thoron was calculated by using a passive time integrating, deposition-based technique. The measured attached and un-attached radon and thoron progeny concentrations have been cross-checked by on-line active technique, i.e., Flow-mode Integrated Sampler. A weak positive correlation has been observed between the two devices. The median value of un-attached fraction was found to be 0.15 and 0.12 for thoron and radon progeny, respectively and found to have a log-normal distribution. A good positive correlation has been observed between radon and thoron progeny concentrations.

Assessment of attached and unattached progeny concentrations of 222Rn/220Rn and their contribution to dose using deposition-based progeny sensors

The exposure of radiation from natural sources to population has become an important issue in terms of radiological protection. Mostly natural radiation comes from radon (222Rn), thoron (220Rn) and their solid short-lived daughter products that are the main threat to public health risk. The results presented in this paper are from a survey carried out in 40 villages of Jammu district, Sub-Mountainous region of Jammu and Kashmir, India, to quantify progeny concentration of radon and thoron using a passive time integrating, deposition-based technique. For estimating the total (attached + unattached) progeny concentration of radon/thoron, direct radon/thoron progeny sensors (DRPS/DTPS) have been used and only attached progeny concentration of radon/thoron has been measured by using wire-mesh capped direct radon/thoron progeny sensors (WM-DRPS/WM-DTPS). The study has been conducted for a period of 1 year during winter, rainy and summer seasons in all 112 dwellings. The exposure time of the sensors was 4 months. In this survey, the variability of progeny concentration of radon and thoron based upon variation in building construction materials and seasons-wise has also been discussed and efforts have been made to provide the reason for these variations. The highest level of progeny concentration of radon/thoron was found in the mud-type dwellings compared with dwellings made of concrete, cement and marble. Indoor and outdoor gamma dose rate (µSvh−1) has also been measured and correlated indoor gamma annual effective dose (µSvy−1) with progeny annual effective dose (µSvy−1).

Outdoor thoron and progeny in a thorium rich area with old decommissioned mines and waste rock

Radon (222Rn), thoron (220Rn) and their decay products may reach high levels in areas of high natural background radiation, with increased risk associated with mining areas. Historically, the focus has mostly been placed upon radon and progeny (RnP), but recently there have been reports of significant contributions to dose from thoron progeny (TnP). However, few direct measurements of TnP exist under outdoor conditions. Therefore, we assessed the outdoor activity concentrations of radon, thoron and TnP in an area of igneous bedrock with extreme levels of radionuclides in the thorium decay series. The area is characterized by decommissioned mines and waste rock deposits, which provide a large surface area for radon and thoron emanation and high porosity enhancing exhalation. Extreme levels of thorium and thoron have previously been reported from this area and to improve dose rate estimates we also measured TnP using filter sampling and time-integrating alpha track detectors. We found high to extreme levels of thoron and TnP and the associated dose rates relevant for inhalation were up to 8 μSvh−1 at 100 cm height. Taking gamma irradiation and RnP into account, significant combined doses may result from occupancies in this area. This applies to recreational use of the area and especially previous and planned road-works, which in the worst case could involve doses as large as 23.4 mSv y−1. However, radon and thoron levels were much more intense on a hot September day than during time-integrated measurements made the subsequent colder and wetter month, especially along the ground. This may be explained by cold air observed flowing out from inside the mines through a drainage pipe adjacent to the measurement stations. During warm periods, activity concentrations may therefore be due to both local exhalation from the ground and air ventilating from the mines. However, a substantially lower level of TnP was measured on the September day using filter sampling, as compared to what was measured with time-integrative alpha track detectors. A possible explanation could be reduced filter efficiency related to the attached progeny of some aerosol sizes, but a more likely cause is an upwards bias on TnP detectors associated with assumed deposition velocity, which may be different in outdoor conditions with wind or a larger fraction of unattached progeny. There is thus a need for better instrumentation when dealing with outdoor TnP.

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 (222Rn), thoron (220Rn) and their decay products in environment may increase the risk of radiological exposure to the mankind. The 222Rn, 220Rn 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 222Rn and 220Rn 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 222Rn and 220Rn was 25 Bqm−3 and 1.8 Bqm−3. The equilibrium factor for 222Rn and 220Rn in studied area was 0.47 ± 0.13 and 0.05 ± 0.03. The equilibrium factor and unattached fraction of 222Rn and 220Rn 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 (fpRn) and equilibrium factor (FRn). The present work also aims to evaluate an accurate expression among available expression in literature for the estimation of fpRn.

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.

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

In this work, the attached and unattached activity size distribution of 222Rn progeny (214Bi and 218Po) 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 214Bi progeny were associated with the aerosol particles of the accumulation mode. The active median aerodynamic diameter (AMAD) of this mode for 214Bi was determined to be 350nm with a geometric standard division (GSD) of 3. The GSD of unattached size distributions for 218Po 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 218Po 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.

Deposition pattern of inhaled radon progeny size distribution in human lung

One of the important factors controlling the distribution of radiation dose to the different portions of the human respiratory tract is the deposition pattern of radon progeny containing aerosol. Based on the activity size distribution parameters of radon progeny, which were measured in Minia University, the deposition behavior of radon progeny (attached and unattached) has been studied by using a stochastic deposition model. The attached fraction was collected using a low pressure Berner cascade impactor technique. A screen diffusion battery was used for collecting the unattached fraction. Most of the attached activities for 222Rn progeny were associated with aerosol particles of the accumulation mode. The bronchial deposition fraction of particles in the size range of attached radon progeny was found to be lower than those of unattached progeny. The effect of radon progeny deposition by adult male has been also studied for various levels of physical exertion. An increase in the breathing rate was found to decrease the fraction with which inhaled progeny were deposited in the bronchi. As the ventilation rate increases from 0.54 to 1.5 m3 h−1, the average deposition fraction of airway generation 1 through 8 are expected to decrease by 22% for 1.4 nm particles and by 38% for 150 nm particles.

Dosimetry modelling of transient radon and progeny concentration peaks: results from in situ measurements in Ikaria spas, Greece

Radon and progeny ((218)Po, (214)Pb, (214)Bi and (214)Po) are radioactive indoor pollutants recognised for the human radiation burden that they induce. Bathing in thermal spas causes transient concentration peaks of radon and progeny and additional short-term impact in patients and personnel. This paper reports a semi-empirical non-linear first order model for describing radon and progeny variations in treatment rooms of the Ikaria spas. Non-measured physical parameters were estimated from in situ measurements in Ikaria through non-linear numerical solving. Exposure and dose variations were additionally modelled. Attachment rate constants were found to be between 0.44 and 55 h(-1). Deposition rate constants were between 0.28 and 7.3 h(-1) for attached nuclei and 0.42 and 64 h(-1) for unattached nuclei. Unattached progeny peaks were right-shifted compared to those of radon. Modelled effective doses ranged between 0.001 mSv per year and 0.589 mSv per year for patients and between 0.001 mSv per year and 18.9 mSv per year for workers. Apollon spas presented quite high doses. These were the highest reported in Greece and are significant worldwide.

Unattached fractions and aerosol attached of radon progeny in indoor air

The present study summarizes the experimental data on the activity concentrations of222Rn gas , unattached and attached short-lived222Rn progeny 218Po, 214Pb and 214Po in indoor air of Jeddah City, K.S.A. Jeddah city lies on the eastern bank of the red sea, South West the Kingdom of Saudi Arabia. The city is located between latitudes 21° 27\ and 21° 30\ N, longitudes 39° 9\ and 31° 12\ E. By means of theoretical model calculation, the unattached fraction (fP) of 218Po, 214Pb of potential alpha energy of 222Rn progeny, the equilibrium factor (F), the attachment rate (X) to aerosol particles in the room air, the attachment coefficient (B) and the deposition rates of unattached (qf) and attached (qa) of 222Rn progeny on walls and other surfaces were calculated. The measurements were performed at different days in three different rooms of same size at low and moderate ventilation rates. An electrostatic precipitation method and a single wire-screen diffusion battery technique were both employed for the determination of 222Rn gas concentration and its unattached progeny, respectively. At low ventilation rate (υ ≤ 0.4 h–1) a mean unattached fraction (fP) of 0.096±0.01 was obtained at a mean aerosol particle concentration (Z) of 2.6×103 cm–3 and at a mean equilibrium factor (F) of 0.34 ± 0.02. The mean deposition rates of unattached (qf) and attached (qa) 222Rn progeny were found to be 94±13 h–1 and 0.12±0.05 h–1, respectively. The values of the recoil factor were neglected. At moderate ventilation rate of υ = 0.5 h–1 a mean value of fP = 0.059±0.006 was obtained at a mean aerosol concentration Z = 29×103 cm–3 and at a mean F = 0.24±0.014. In this case the mean value of the recoil factor was found to be 0.54±0.18. Key words: Unattached fraction, aerosol attached, theoretical model calculation, radon progeny.

Long-term determination of airborne radon progeny concentrations using LR 115 solid-state nuclear track detectors

This paper described the establishment of lognormal distributions for the Jacobi room model parameters with a view to improve an existing method for long-term passive measurements of the equilibrium factor using LR 115 solid-state nuclear track detectors, namely, through the proxy equilibrium factor ( F p ) method. F p is defined as ( C 1 + C 3 )/ C 0 where C 0 , C 1 and C 3 are the concentrations of 222 Rn, and the airborne concentrations of 218 Po and 218 Po (or 214 Bi), respectively. The studied Jacobi room model parameters included the ventilation rate λ v , the aerosol attachment rate λ a , the deposition rate λ d u of unattached progeny and the deposition rate λ d a of attached progeny. The lognormal distributions generated more realistic distributions for the equilibrium factor F and the unattached fraction f p of the potential alpha energy concentration, and a much tighter relationship between F and F p , when compared with the traditionally used uniform distributions. With the new relationship between F and F p , the accuracy of the F p method to determine F from F p is significantly improved.

Inhalation dose assessment of indoor radon progeny using biokinetic and dosimetric modeling and its application to Jordanian population

High indoor radon concentrations in Jordan result in internal exposures of the residents due to the inhalation of radon and its short-lived progeny. It is therefore important to quantify the annual effective dose and further the radiation risk to the radon exposure. This study describes the methodology and the biokinetic and dosimetric models used for calculation of the inhalation doses exposed to radon progeny. The regional depositions of aerosol particles in the human respiratory tract were firstly calculated. For the attached progeny, the activity median aerodynamic diameters of 50 nm, 230 nm and 2500 nm were chosen to represent the nucleation, accumulation and coarse modes of the aerosol particles, respectively. For the unattached progeny, the activity median thermodynamic diameter of 1 nm was chosen to represent the free progeny nuclide in the room air. The biokinetic models developed by the International Commission on Radiological Protection (ICRP) were used to calculate the nuclear transformations of radon progeny in the human body, and then the dosimetric model was applied to estimate the organ equivalent doses and the effective doses with the specific effective energies derived from the mathematical anthropomorphic phantoms. The dose conversion coefficient estimated in this study was 15 mSv WLM−1 which was in the range of the values of 6–20 mSv WLM−1 reported by other investigators. Implementing the average indoor radon concentration in Jordan, the annual effective doses were calculated to be 4.1 mSv y−1 and 0.08 mSv y−1 due to the inhalation of radon progeny and radon gas, respectively. The total annual effective dose estimated for Jordanian population was 4.2 mSv y−1. This high annual effective dose calculated by the dosimetric approach using ICRP biokinetic and dosimetric models resulted in an increase of a factor of two in comparison to the value by epidemiological study. This phenomenon was presented by the ICRP in its new published statement on radon.

The HMGU thoron experimental house: a new tool for exposure assessment

A thoron experimental house was constructed in a laboratory room of Helmholtz Zentrum München to perform exposure studies of thoron and its decay products under controlled conditions. The single room house (7.1 m(3)) was built from unfired clay stones and clay plaster. For the plaster of the inner side, the clay was mixed with granite powder enriched with (232)Th. The thoron inventory increased by this means to about 1700 Bq and the progeny potential alpha energy to 130 µJ inside the room. The instrumentation of the experimental house includes active and passive devices for thoron and thoron decay product measurement including attached and unattached progeny, for aerosol particle number and size measurement and characterisation of the climatic conditions. Various parameters as ventilation rate and aerosol concentration can be adjusted. Experiments performed in the experimental house demonstrate the experimental power of this new tool for indoor thoron exposure assessment.

Long-term determination of airborne concentrations of unattached and attached radon progeny using stacked LR 115 detector with multi-step etching

We developed the theoretical basis for long-term determination of airborne concentrations of unattached and attached radon progeny. The work was separated into two parts. First, we showed that (stacked and multiply etched) LR 115 detectors could be used to determine airborne concentrations of the short-lived radon progeny, 218Po and 214Bi. The equilibrium factor F between radon and its progeny could then be determined through the use of the reduced equilibrium factor F red . The airborne concentrations of 214Pb could then be determined. Second, we developed a method based on the airborne concentrations of 218Po, 214Pb and 214Bi to determine the parameters of the Jacobi room model, viz., the ventilation rate λ v , aerosol attachment rate λ a , deposition rate of unattached progeny λ d u and the deposition rate of attached progeny λ d u . With these parameters, the unattached fraction f p of the potential alpha energy concentration could also be determined. Knowledge of f p , together with F, would enable more accurate determination of the effective dose in the human lung.

Development of an integrated sampler based on direct 222Rn/ 220Rn progeny sensors in flow-mode for estimating unattached/attached progeny concentration

A flow-mode integrated sampler consisting of a wire-mesh and filter-paper array along with passive solid state nuclear track detectors has been developed for estimating unattached and attached fraction of 222Rn/ 220Rn progeny concentration. The essential element of this sampler is the direct 222Rn/ 220Rn progeny sensor (DRPS/DTPS), which is an absorber-mounted-LR115 type nuclear track detector that selectively registers the alpha particles emitted from the progeny deposited on its surface. During sampling at a specified flow-rate, the unattached progeny is captured on the wire-mesh; while the attached progeny gets transmitted and is captured on the filter-paper. The alpha particles emitted by the deposited progeny atoms are registered on the sensors placed at a specified distance facing the wire-mesh and the filter-paper, respectively. The various steps involved in the development of this flow-mode direct progeny sampler such as the optimization of the sampling rate and the distance between the sensor and the deposition substrate are discussed. The sensitivity factor of the DTPS-loaded sampler for 220Rn progeny deposited on the wire-mesh and filter-paper is found to be 23.77 ± 0.64 (track cm −2 h −1) (Bq m −3) −1 and 22.30 ± 0.18 (track cm −2 h −1) (Bq m −3) −1, respectively; while that of DRPS-loaded sampler for 222Rn progeny deposition, is 3.03 ± 0.14 (track cm −2 h −1) (Bq m −3) −1 and 2.08 ± 0.07 (track cm −2 h −1) (Bq m −3) −1, respectively. The highlight of this flow-mode sampler is its high sensitivity and that it utilizes the passive technique for estimating the unattached and attached progeny concentration, thus doing away with the alpha counting procedures.

DETERMINATION OF PARAMETERS OF THE JACOBI ROOM MODEL USING THE BROWNIAN MOTION MODEL

Parameters of the Jacobi room model were estimated with simulation of Brownian motion. Deposition on internal room surfaces and attachment of progeny atoms to three modally distributed aerosols were taken into account. The values of parameters were presented as functions of aerosol concentrations. The deposition rate of an unattached progeny was estimated in the range 30-47 h-1; the deposition rate of an attached progeny was very small and its range is 0.0007-0.004 h-1; the attachment rate of a progeny is in range 40-170 h-1. The statistical uncertainty was lower than 1%. The ranges of parameters were similar to those reported in literature.

Exposures to 222Rn and its progeny derived from implanted 210Po activity

The Jacobi room model was applied to study the relative contributions from the unattached and attached fractions to the implanted activity of 210Po. It was found that under normal conditions, about 85% of the implantation was due to the unattached fraction. Sensitivity analysis was performed to identify the most important factors that influence the deposition and implantation of radon progeny. The main factors affecting the incorporation of 210Po are the attachment rate, deposition rate of unattached progeny and the surface to volume ratio of the room. The calibration curves, which related the 210Po activity per unit surface area to the concentrations of 222Rn and of the radon progeny, were determined as functions of exposure times. The implanted activity is found to distribute close to a lognormal distribution. For an exposure of 20 years, the distribution has a geometric standard deviation of 2.2 and a geometric mean of 0.023 Bq / m 2 / ( Bq / m 3 ). The last value is considered as the calibration coefficient of the glass response in terms of the implanted 210Po activity per unit surface area per unit concentration of 222Rn for an exposure period of 20 years.