Thoron Progeny Concentrations Research Articles

Assessment of Radiological Risks due to Indoor Radon, Thoron and Progeny, and Soil Gas Radon in Thorium-Bearing Areas of the Centre and South Regions of Cameroon

Indoor radon, thoron and thoron progeny concentrations, along with the equilibrium factor for thoron progeny and soil gas radon concentrations, have been measured to assess radiological risks in the centre and south regions of Cameroon. Indoor radon and thoron concentrations were estimated using radon–thoron discriminative detectors (RADUET), while thoron progeny monitors measured the equilibrium equivalent thoron concentration (EETC). Radon concentrations in the soil were determined using a MARKUS 10 detector. It was found that radon, thoron and thoron progeny concentrations range between 19 and 62 Bq m−3, 10 and 394 Bq m−3 and 0.05 and 21.8 Bq m−3, with geometric means of 32 Bq m−3, 98 Bq m−3 and 4.9 Bq m−3, respectively. The thoron equilibrium factor ranges between 0.007 and 0.24, with an arithmetic mean of 0.06 ± 0.03; this is higher than the world average value of 0.02 provided by the United Nations Scientific Commission on the Effects of Atomic Radiation(UNSCEAR, New York, USA). The level of the soil radon concentration ranges from 4.8 to 57.3 kBq m−3, with a geometric mean of 12.1 kBq m−3 at a depth of 0.7 m. Of the sampling points, 66% fall within normal radon risk areas, and 3% of the sampling areas are high radon risk areas exceeding 50 kBq m−3. The annual effective dose was found to be 0.03 ± 0.01 mSv for radon, 0.08 ± 0.05 mSv for thoron, 0.63 ± 0.12 mSv for radon progeny and 1.40 ± 0.84 mSv for thoron progeny. The total dose is estimated to be 2.14 mSv y−1. The mean estimated indoor excess lifetime cancer risk values due to radon, thoron, radon progeny and thoron progeny are 0.12 × 10−3, 0.31 × 10−3, 2.51 × 10−3 and 5.58 × 10−3, respectively. Thoron progeny contributed 60% to the effective dose. Thus, thoron progeny cannot be neglected in dose assessments, in order to avoid biased results in radio-epidemiological studies.

Radiological dose estimation due to exposure to attached and unattached fractions of radon and thoron progeny concentrations

Radiological dose estimation due to exposure to attached and unattached fractions of radon and thoron progeny concentrations

Exposures from radon, thoron, and thoron progeny in high background radiation area in Takandeang, Mamuju, Indonesia

Abstract The exposure from radon, thoron, and thoron progeny was measured for 45 dwellings in high background radiation area in Takandeang, Indonesia with ambient dose equivalent rate ranging from 0.34 μSv h−1 to 1.90 μSv h−1. The measurement was taken using passive radon and thoron discriminative detector and thoron progeny detector. This measurement was taken from November 2018 to October 2019, and within one month the detector would be replaced with a new detector. The concentrations of radon, thoron, and thoron progeny were calculated as 42–490 Bq m−3, 20–618 Bq m−3, and 4–40 Bq m−3, respectively. The concentrations for outdoor were 49–435 Bq m−3, 23–457 Bq m−3, and 4–37 Bq m−3, respectively, and the annual effective dose was 9.8–28.6 mSv y−1. Based on the result of Spearman’s correlations analysis between the indoor radon and thoron concentrations and between the indoor thoron progeny and thoron concentrations, we suggest that exposure to thoron cannot be predicted from exposure to radon, and the equilibrium equivalent thoron concentration has a large uncertainty when it is estimated from thoron concentration assuming a single thoron equilibrium factor.

The Importance of Direct Progeny Measurements for Correct Estimation of Effective Dose Due to Radon and Thoron.

Radon (Rn), thoron (Tn), and thoron progeny (TnP) were measured in seven inhabited areas of the uranium and thorium bearing region of Lolodorf, located in southwestern Cameroon. Then the equilibrium factor (FTn) between thoron and its progeny was determined in order to show the importance of direct progeny measurements for correct estimation of effective dose due to radon, thoron and their progenies. A total of 220 RADUET detectors were used to measure indoor radon and thoron and 130 TnP monitors for thoron progeny indoors. The arithmetic and geometric mean concentrations of Rn, Tn, and TnP were 103 and 89 Bq m−3, 173, and 118 Bq m−3, 10.7, and 7.4 Bq m−3, respectively. Total effective dose determined from radon, thoron, and their progenies was estimated at 4.2 ± 0.5 mSv y−1. Thoron equilibrium factor varied according to seasons, the type of dwelling, building materials and localities. Thoron (Tn and TnP) contribution to effective dose ranged between 3 and 80% with the average value of 53%. Total effective dose estimated from the world average equilibrium factor of 0.02 given by UNSCEAR was 2.7 ± 0.2 mSv y−1. The effective dose due to thoron varied greatly according to the different values taken by FTn and was different from that determined directly using TnP concentrations. Thus, effective dose due to thoron determined from the equilibrium factor is unreliable. Therefore, the risk of public exposure due to thoron (Tn and TnP) may therefore be higher than that of radon (Rn and RnP) in many parts of the world if FTn is no longer used in estimating total effective dose. This is not in contradiction with the UNSCEAR conclusions. It is therefore important to directly measure the radon and thoron progeny for a correct estimate of effective dose.

Simultaneous measurements of indoor radon and thoron and inhalation dose assessment in Douala City, Cameroon

ABSTRACTRadon, thoron and associated progeny measurements have been carried out in 71 dwellings of Douala city, Cameroon. The radon–thoron discriminative detectors (RADUET) were used to estimate the radon and thoron concentration, while thoron progeny monitors measured equilibrium equivalent thoron concentration (EETC). Radon, thoron and thoron progeny concentrations vary from 31 ± 1 to 436 ± 12 Bq m–3, 4 ± 7 to 246 ± 5 Bq m–3, and 1.5 ± 0.9 to 13.1 ± 9.4 Bq m–3. The mean value of the equilibrium factor for thoron is estimated at 0.11 ± 0.16. The annual effective dose due to exposure to indoor radon and progeny ranges from 0.6 to 9 mSv a–1 with an average value of 2.6 ± 0.1 mSv a–1. The effective dose due to the exposure to thoron and progeny vary from 0.3 to 2.9 mSv a–1 with an average value of 1.0 ± 0.4 mSv a–1. The contribution of thoron and its progeny to the total inhalation dose ranges from 7 to 60 % with an average value of 26 %; thus their contributions should not be neglected in the inhalation dose assessment.

A study of seasonal variations of radon, thoron and their progeny levels in different types of dwellings in Faridabad district, Southern Haryana, India

Radon, thoron and their progeny are responsible for more than 50% of the total ionizing radiation dose received by human population. In the present work, radon, thoron and their progeny concentration measurements have been carried out in 150 dwellings in different villages of Faridabad district of Haryana, India. Pin-holes based twin cup dosimeter containing LR-115 type-II film (solid state nuclear track detectors) has been used for the time-integrated passive measurement of radon and thoron concentrations. The dosimeters were deployed for three seasons each having 4 months of exposure period. For measurement of radon and thoron progeny concentration (EERC/EETC), deposition based direct radon/thoron progeny sensors (DRPS/DTPS) were deployed with dosimeters. Based on the gamma exposure rate in different villages during preliminary survey and type of houses available in the regions, numbers of dwellings of different categories have been selected. Radon, thoron and their progeny concentration and total annual effective inhalation dose were calculated and compared with the recommended limits by UNSCEAR, ICRP and WHO.

ANNUAL EFFECTIVE DOSE ASSESSMENT DUE TO RADON AND THORON PROGENIES IN DWELLINGS OF KILIMAMBOGO, KENYA.

Human beings are continuously exposed to ionising radiation originating from natural or artificial sources. Uranium-238 and Thorium-232 found in building materials are important sources of radon and thoron in the indoor environment. The concentration levels of radon, thoron and thoron progeny were measured in mud-walled, metallic or iron sheet-walled and stone-walled modern houses in Kilimambogo region, Kenya for 3 months. Radon and thoron concentration levels were measured using passive radon-thoron discriminative monitors (RADUET), while thoron progeny concentrations as the equilibrium equivalent thoron concentration (EETC) were measured using thoron progeny monitors. The mean radon concentration levels in mud, metallic and stone-walled dwellings were 67 ± 11, 60 ± 10 and 75 ± 10 Bq m-3, respectively. The mean thoron concentration levels in the corresponding dwellings were 195 ± 36, 71 ± 24 and 161 ± 31 Bq m-3, respectively, while EETCs were 12 ± 2, 3 ± 1 and 7 ± 1 Bq m-3, respectively. The annual effective doses for radon were 1.3 ± 0.2, 1.1 ± 0.1 and 1.4 ± 0.2 mSv y-1 in mud, metallic and stone-walled houses while those from thoron estimated from EETC were 2.4 ± 0.4, 0.5 ± 0.1 and 1.5 ± 0.2 mSv y-1 in the corresponding houses, respectively.

Proposal and optimization of method for direct determination of the thoron progeny concentrations and thoron equilibrium

Most studies focused on thoron have shown that indoor thoron originates mainly from building materials and that thoron concentrations exponentially decrease with a distance from a wall surface. On the contrary, due to longer half-lives of thoron progenies, 212Pb and 212Bi, which are mainly responsible for the bronchial dose, it is expected that their spatial distribution is homogeneous. Therefore, direct measurements of thoron progeny concentrations or direct thoron measurement and determination of thoron equilibrium factor are necessary for accurate dose assessment. In this paper, we have optimized and validated a reliable and inexpensive method for direct measurement of thoron progenies concentrations based on an air filtration followed by gamma spectrometry measurements. With simultaneous measurements of indoor thoron by the RAD7 active device, the equilibrium factor for thoron in 15 different investigated dwellings was estimated. Obtained results for the equilibrium equivalent thoron concentrations in the range from 0.277 Bq/m3 to 11.34 Bq/m3 and thoron equilibrium factor in the range from 0.0047 to 0.098 with arithmetic mean value of 0.034 are in good agreement with already published results.

Measurements of radon (222Rn) and thoron (220Rn) exhalations and their decay product concentrations at Indian Stations in Antarctica

During the 33rd summer expedition to the two Indian Stations at Antarctica, Bharati and Maitri, radon and thoron progeny concentrations in indoors and outdoors were measured along with radon (222Rn)/thoron (220Rn) exhalation rate measurements of soil samples, radionuclide content and 222Rn emanation coefficient. This investigation was based on the reports of the higher gamma radiation levels reported around these stations. The results will give an estimate of the radioactivity level as well as the total dose received by personnel carrying out long-term measurements at these stations. Radon and thoron progeny concentrations were measured using direct radon and thoron progeny sensors (DRPS and DTPS). The soil radionuclide content was measured using HPGe gamma spectrometry while radon/thoron exhalation rates were measured using the accumulation method by scintillation radon/thoron monitor. In contrast to a higher radiation field and radioactivity content, studies showed the radon/thoron exhalation rates and progeny concentration to be similar to that measured in normal background areas of other parts of the world. This could be attributed to the ice deposits and the larger atmospheric dispersion, and also to the soil nature which is mainly loamy sands with low clay content contributing to a lower emanation. The results are discussed.

RADON AND THORON PROGENY IN DUTCH DWELLINGS.

Radon and thoron progenies in Dutch dwellings cause ~400 cases of lung cancer per year. Some 30% of the risk is due to thoron progeny, which demonstrates that the influence of thoron progeny is much larger than previously anticipated. This was concluded from a national survey in 2500 Dutch dwellings, built since 1930. Radon concentrations (15.6 ± 0.3 Bq m-3 on average) are correlated to type of dwelling, year of construction, ventilation system, location (soil type) and smoking behaviour of inhabitants. The survey data support the establishment of a comparatively low national reference level for radon in dwellings in the Netherlands of 100 Bq m-3, in line with recommendations by WHO and ICRP. Some 24 thousand of the 6.2 million dwellings in the Netherlands (built since 1930) are expected to exceed this level. Around 80% of these are located in the relatively small group of naturally ventilated single-family houses in two designated geographical areas. Radon concentrations above 200 Bq m-3 are rare in the Netherlands and simple and inexpensive measures will be sufficient to reduce enhanced radon concentrations to values below the national reference level. Thoron progeny concentrations (0.64 Bq m-3, on average) show correlations with year of construction and smoking behaviour. In 75 additional dwellings, a pilot study was conducted to determine the relationship between the exhalation of thoron from walls and the concentration of thoron progeny in the room. Thoron exhalation values exceeding the median value of 2.2 × 10-2 Bq m-2 s-1 by a factor 10 or more were found frequently, but enhanced concentrations of thoron progeny were measured only occasionally. Under very unfavourable conditions, however, for instance if phosphogypsum is applied as finishing material on all walls and ceilings in the house, strongly elevated thoron progeny concentrations may occur. This survey yielded a maximum recording of 13.3 Bq m-3. There is no reason to expect that such levels are specific to the Netherlands, indicating that in other regions with low radon levels, thoron may be a more important contributor to the population dose as well.

Continuous measurement of equilibrium equivalent radon/thoron concentration using time-integrated flow-mode grab sampler

The continuous measurement of any physical entity is the finest approach to see the real-time variation of any concentration. In the present study, an effort has been made to see the continuous variation of radon and thoron progeny concentration (EERC and EETC) using time-integrated flow-mode sampler in which the deposition of progeny particles has been done in the filter paper in which an absorber has been mounted which specifically absorbs the alpha energies emitted by the progenies of radon or thoron. Also, the variation of thoron progeny concentration (EETC) using two different types of SSNTDs, LR-115 and CR-39, has been seen and it has been found that the measurement of EETC using both of the detectors is very much comparable with positive relationship (R = 0.89) between the results obtained.

Thoron exposure in Dutch dwellings – An overview

In the Netherlands considerable attention has been given to the exposure from thoron progeny in dwellings. For this purpose a nationwide survey on the thoron exhalation and thoron progeny concentration has been completed in 2015. Furthermore, extensive laboratory studies have been performed to measure activity concentrations and thoron exhalation rates from regular Dutch building materials. The purpose of this study is to demonstrate if the findings from both field experiments and laboratory results are consistent. For this reason measured properties of building materials and surface barriers, in-situ measurements on air ventilation and thoron(progeny) in dwellings as well as advanced computational modelling on indoor air and aerosol behaviour have been used. The results demonstrate that median and mean thoron progeny concentrations of 0.53 and 0.64 Bq·m−3 found in the survey are comparable with the mean concentration of 0.57 Bq·m−3 obtained from laboratory testing and calculation. Furthermore, upper thoron progeny concentrations from the survey and the calculations are with respectively 13 and 14 Bq·m−3 also in good agreement. Such elevated concentrations lead to an effective doses of around 4 mSv per year. The study also includes worst-case scenarios on the application of surface materials high on 232Th, and the expected reduction in thoron progeny when using mainstream mitigation measures.

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.

Stable control of thoron progeny concentration in a thoron chamber for calibration of active sampling monitors

Long-term stability and homogeneity of activity concentration in a calibration facility are vital to quality assurance and quality control for measuring thoron and its progeny. The long half-life of 212Pb leads to difficulty for attaining highly stable activity; thus, the development of a compensation system based on air recirculation between the ageing chamber and thoron chamber is presented to make up for thoron progeny losses incurred due to plate-out, decay and sampling in the thoron chamber. Stable concentration of thoron progeny in the ageing chamber is dependent on a constant solid 220Rn source and certain aerosol concentration. A recirculation loop with various flow-rates below 1.6 m3 h−1 simulates air sampling of instruments being calibrated in the thoron chamber to eliminate concentration fluctuations. A theoretical model is derived for estimating the effect of main variables on the stable concentrations of 212Pb. Variable but stable activity concentrations of 212Pb are produced under different compensation and simulation flow-rates by this method with the coefficient of variation below 10% for the activity concentrations of thoron progeny. Concentration ratios of C(212Bi)/C(212Pb), ranging between 0.33 and 1, are achieved under different ventilation rates for the system.

Radiation dose due to radon and thoron progeny inhalation in high-level natural radiation areas of Kerala, India

In order to evaluate internal exposure to radon and thoron, concentrations for radon, thoron, and thoron progeny were measured for 259 dwellings located in high background radiation areas (HBRAs, outdoor external dose: 3–5 mGy y−1) and low background radiation areas (control areas, outdoor external dose: 1 mGy y−1) in Karunagappally Taluk, Kerala, India. The measurements were conducted using passive-type radon-thoron detectors and thoron progeny detectors over two six-month measurement periods from June 2010 to June 2011. The results showed no major differences in radon and thoron progeny concentrations between the HBRAs and the control areas. The geometric mean of the annual effective dose due to radon and thoron was calculated as 0.10 and 0.44 mSv, respectively. The doses were small, but not negligible compared with the external dose in the two areas.

Long-term measurements of residential radon, thoron, and thoron progeny concentrations around the Chhatrapur placer deposit, a high background radiation area in Odisha, India

The Chhatrapur placer deposit is found in a high background radiation area which has been recently identified on the southeastern coast of India. Previously, some geochemical studies of this area were carried out to assess external dose from radionuclides-bearing heavy mineral sands. In this study, radon, thoron and thoron progeny concentrations were measured in about 100 dwellings during three seasons (autumn-winter, summer, and rainy) in a 10- to 12-month period and annual doses due to inhalation of them were evaluated. The measurements were made by passive-type radon-thoron discriminative detectors and thoron progeny detectors in which solid state nuclear track detectors were deployed. The results show that radon and thoron concentrations differ by one order of magnitude depending on exposure periods, while thoron progeny concentration is nearly constant throughout the year. Since thorium-rich sand is distributed in the studied area, exposure to thoron is equal to, or exceeds, exposure to radon and is not negligible for dose evaluation. Based on the measurements, doses due to inhalation of radon and thoron are evaluated as 0.1–1.6 mSv y−1 and 0.2–3.8 mSv y−1, respectively. The total dose is 0.8–4.6 mSv y−1, which is the same order of magnitude as the worldwide value.

ASSESMENT OF INDOR RADON, THORON AND THEIR PROGENY LEVELS IN RESIDENTIAL HOUSES OF HARDOI, UTTAR PRADESH, (INDIA)

Radon, thoron and their progeny levels are significant natural sources of radiation exposure for the general population in both living and working places. The concentration of radon varied from 15 Bq/m3 to 78 Bq/m3 with an average of 46 Bq/m3, while thoron concentration varied from 11 Bq/m3 to 26 Bq/m3 with an average of 18 Bq/m3.
 The concentration of radon progeny (EERC) varied from 10 Bq/m3 to 26 Bq/m3 with an average of 18 Bq/m3, while the concentration of thoron progeny (EETC) varied from 0.56 Bq/m3 to 1.91 Bq/m3 with an average of 1.11 Bq/m3. The value of the equilibrium factor for radon varied from 0.19 to 0.76 with an average of 0.37 while for thoron it varied from 0.02 to 0.12 with an average of 0.06.
 Our experimental finding confirmed that the indoor radon, thoron and their progeny concentration were within internationally accepted norms.

Radon and thoron progeny integrated measurement based on high-voltage sampling

ABSTRACTFor the purpose of directly measuring radon and thoron progeny concentrations simultaneously, an unattended battery-operated progeny measurement (UBPM) device, which samples aerosol particles in an electric field, was improved by adopting two different thickness aluminum foils for alpha particles discriminating. The equations for the calculation of the results were derived, and a series of calibration experiments and comparison tests were carried out in the potential alpha energy concentration calibration chamber in BfS Berlin and the HMGU experimental thoron house, respectively. Results show that the calibration coefficients are stable in different levels of radon and thoron progeny. The lower level detection limits of the device for radon and thoron progeny concentration are 1.22 and 0.14 Bq m−3, respectively, for three months exposure. The instrument proved to be independent from environmental conditions in ordinary living room conditions (humidity <65% RH, aerosol particle concentration >1500 cm−1). Comparison results show that the measurement results of the UBPM device are comparable with the reference instrument and suitable for long-term radon and thoron survey in dwellings.

Impact from indoor air mixing on the thoron progeny concentration and attachment fraction

Despite the considerable amount of work in the field of indoor thoron exposure, little studies have focussed on mitigation strategies to reduce exposure to thoron and its progeny. For this reason an advanced computer model has been developed that describes the dispersion and aerosol modelling from first principal using Computational Fluid Dynamics. The purpose of this study is to investigate the mitigation effects from air mixing on the progeny concentration and attachment with aerosols. The findings clearly demonstrate a reduction in thoron progeny concentration due to air mixing. The reduction in thoron progeny is up to 60% when maximum air mixing is applied. In addition there is a reduction in the unattached fraction from 1.2% under regular conditions to 0.3% in case of maximum mixing.

MEASUREMENT OF RADON, THORON AND THEIR PROGENY CONCENTRATIONS IN THE DWELLINGS OF PAURI GARHWAL, UTTARAKHAND, INDIA.

It is well known that inhalation of radon, thoron and their progeny contributes more than 50 % of natural background radiation dose to human being. The time-integrated passive measurements of radon, thoron and their progeny concentrations were carried out in the dwellings of Pauri Garhwal, Uttarakhand, India. The measurements of radon and thoron concentrations were performed by LR-115 detector-based single-entry pin-hole dosemeter, while for the measurement of progeny concentrations, LR-115 deposition-based direct radon and thoron progeny sensors technique was used. The experimental techniques and results obtained are discussed in detail.