Thoron Gas Concentration Research Articles

A study of radon, thoron and annual effective dose in some Egyptian dwellings by twin-cup dosimeter technique with LR-115 detectors

In the present study, Solid State Nuclear Track Detectors (LR-115–type II) based twin-cup dosimeters were used for estimating radon (222Rn) and thoron (220Rn) gas concentration levels in the environmental air of thirty dwellings in ten cities in Egypt. In the studied dwellings radon concentration levels were found to vary from 24.80 ± 3.98 to 39.71 ± 8.71 Bq m−3 with an average of 32.64 ± 4.34 Bq m−3 whereas thoron concentration is found to vary from 10.46 ± 2.87 to 15.41 ± 2.72 Bq m−3 with an average of 12.48 ± 1.58 Bq m−3. The total annual effective dose by the inhabitants of these dwellings due to radon and thoron was found below the recommended limit by the international agencies. The present study concluded that the dwellings are safe without posing significant radiological threats to human beings.

Pengukuran Konsentrasi Gas Radon (222Rn) dan Thoron (220Rn) Menggunakan Detektor CR-39 Pada Rumah Penduduk Di Nagari Alam Pauh Duo, Solok Selatan

Telah dilakukan pengukuran konsentrasi gas radon (222Rn) dan gas thoron (220Rn) menggunakan metode pasif CR-39 pada rumah penduduk di Nagari Alam Pauh Duo, Kabupaten Solok Selatan. Pengukuran bertujuan untuk mengetahui dosis efektif yang diterima oleh penduduk di daerah tersebut. Pengukuran gas radon dan gas thoron dilakukan menggunakan 50 buah detektor CR-39 yang dipasang pada 3 lokasi selama 3 bulan. Hasil pengukuran konsentrasi gas radon terkecil yaitu 7 ± 0,50 Bq/m3 sampai dengan yang terbesar yaitu 37 ± 2,65 Bq/m3 dengan rata-rata 14 ± 0,99 Bq/m3, sedangkan konsentrasi gas thoron yang terkecil yaitu 3 ± 0,18 Bq/m3 dan yang terbesar yaitu 25 ± 1,78 Bq/m3 dengan rata-rata 6,25 ± 0,45 Bq/m3. Hasil konsentrasi gas radon dan gas thoron yang didapatkan masih di bawah batas yang direkomendasikan oleh UNSCEAR tahun 2008 yaitu 300 Bq/m3. Estimasi dosis efektif yang diterima penduduk akibat paparan gas radon dan gas thoron yaitu 0,94 mSv/tahun dan 0,63 mSv/tahun. Nilai dosis efektif yang didapatkan tidak melebihi ambang batas yang telah direkomendasikan oleh PERKA BAPETEN No. 4 pasal 23 ayat 1 tahun 2013 yaitu 1 mSv/tahun.

Measurement of Indoor Thoron Gas Concentrations Using a Radon-Thoron Discriminative Passive Type Monitor: Nationwide Survey in Japan.

As part of a nationwide survey of thoron (220Rn) in Japan, the indoor 220Rn gas concentrations in 940 dwellings were measured throughout one year, from 1993 to 1996, using a passive type 222Rn-220Rn discriminative monitor. The monitor was placed in a bedroom or a living room in each house for four successive three-month periods. The mean annual indoor 220Rn concentration was estimated from the four measurements in each house. The arithmetic mean, the median and the geometric mean for indoor 220Rn concentrations in 899 dwellings were 20.1, 9.6 and 10.0 Bq m−3, respectively. The 220Rn concentrations exhibited a log-normal distribution. It was found that the 220Rn concentrations were dependent on the nature of the materials used for wall construction and also on the distance of measurement from the wall. Significant seasonal variations in the 220Rn concentration were not observed. It would seem that the nature of the wall material contributed to the increased indoor 220Rn concentrations.

Inspection and radiation dose evaluation results for NORM-containing products in Taiwan

In 2018, “negative ion powder” mattress produced by a South Korean manufacturer producing a dose rate of > 1 mSv/year, was found to have monazite powder in it. In order to verify if other products advertised as containing “negative ion powder” were also hazardous, an investigation had been carried out by the Atomic Energy Council and Institute of Nuclear Energy Research in Taiwan. By the end of April 2019, 11 kinds and a total of 59 samples were inspected for radon content. The radiation doses for the samples were evaluated using Atomic Energy Council approval evaluation setup which was established according to the characteristics of the products. The highest concentration of 220Rn among the inspected mattresses was over 10 kBq/m3 and the evaluated annual dose was about 78.5 mSv. The linearity of the surface dose rate and the measured thoron gas concentration for the mattress samples was also discussed in this study.

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.

Variation of ambient gamma dose rate and indoor radon/thoron concentration in different villages of Udhampur district, Jammu and Kashmir State, India

The exposure of natural background radiation imparts a major contribution to inhalation doses received by the public, and its amount depends on the lithology, altitude, and building construction materials. The preliminary results of indoor and outdoor gamma-ray dose rate of Udhampur district, Jammu and Kashmir, India are presented. Indoor radon and thoron gas concentration have also been measured by using the LR-115 based pin-hole detectors in the same villages and the estimated concentrations are within the recommended level of the International Commission of Radiological Protection. For the outdoor environment, the minimum and maximum gamma dose rate were 0.06 and 0.4 μSvh−1, whereas for indoor environment, the minimum and maximum gamma dose rates were 0.09 and 0.21 μSvh−1, respectively. Effects of lithology on indoor radon/thoron concentration and also on gamma dose rates have also been investigated. The average values of annual effective dose from background gamma radiations were well within the safe limit and does not cause health hazard to the inhabitants.

ASSESSMENT OF INDOOR RADIATION DOSE RECEIVED BY THE RESIDENTS OF NATURAL HIGH BACKGROUND RADIATION AREAS OF COASTAL VILLAGES OF KANYAKUMARI DISTRICT, TAMIL NADU, INDIA

Radiation exposure and effective dose received through two routes of exposure, viz. external and internal, via inhalation, by residents of coastal villages belonging to Natural High Background Radiation Areas (NHBRA) of Kanyakumari District and Tamil Nadu inIndiawere studied. While the indoor gamma radiation levels were monitored using Thermo Luminescent Dosimeters (TLDs), the indoor radon and thoron gas concentrations were measured using twin chamber dosimeters employing Solid State Nuclear Track Detectors (SSNTDs, LR-115-II). The average total annual effective dose was estimated and found to be varied from 2.37 to8.64 mSv.

Is thoron a problem in Swedish dwellings? Results of measurements of concentrations of thoron and its progeny.

Long-term measurements of thoron progeny concentrations (equilibrium-equivalent thoron concentration) have been carried out in Swedish dwellings with the aim of investigating if thoron and its progeny pose a health risk. Measurements were performed in 93 houses and 25 apartments. In addition to thoron progeny concentration, thoron gas concentration near the wall surface, ambient dose equivalent rate of gamma radiation and radon gas concentration were also measured. The results show that the mean value of thoron progeny was 2.2 Bq m(-3) in houses and 1.6 Bq m(-3) in apartments. Ten per cent of the dwellings (both houses and apartments) had thoron progeny concentrations exceeding 10 Bq m(-3). Thoron progeny concentration is not significantly different in dwellings built of alum shale-based aerated concrete ('blue concrete') than dwellings built of other construction materials. For the dwellings in this study (not representative of the Swedish population), the mean dose estimated due to exposure to thoron was found to be 0.4 mSv y(-1).

Annual Effective Dose Due to Radon, Thoron and their Progeny in Dwellings of Aligarh City and around a Thermal Power Station in Aligarh District, U.P., India

The present study was conducted to measure integrated radon and thoron concentration levels in dwellings of Aligarh city and around the thermal power station situated in Aligarh District. Solid State Nuclear Track Detectors (LR-115, TYPE-II) based twin cup dosimeters were used for this purpose. Radon and thoron progeny concentration levels in terms of Potential Alpha Energy Concentrations (PAECs) and annual effective dose received by the inhabitants in studied dwellings were estimated from observed values of radon and thoron gas concentrations. The evaluated mean values of radon and thoron gas concentration in Aligarh city were 30.3 Bqm-3 (SD =10.6) and 10.2 Bqm-3 (SD =6.1) respectively and around thermal power station 23.6Bqm-3(SD = 5.2) and 7.7 Bqm-3 (SD= 1.9) respectively. The evaluated mean value of radon and thoron progeny concentration were 3.3 mWL (SD=1.1) and 1.1 mWL (SD= 0.7) respectively, in Aligarh city and 2.6 mWL (SD=0.6) and 0.8 mWL (SD= 0.2) around thermal power station. The estimated average value of annual effective dose in studied dwellings was 0.9 mSv (SD= 0.3) in Aligarh city and 0.7 mSv (SD= 0.2) around thermal power station.

Measurement of Indoor Radon, Thoron in Dwelling of Delhi, India Using Double Dosimeter Cups with SSNTDS

In present study, Solid State Nuclear Track Detectors (SSNTDS) based twin chamber dosimeter cups were used for estimating Radon (222Rn) and Thoron (220Rn) gas concentration levels in the environmental air of normal background radiation area in thirty one dwellings of Dwarka city of New Delhi, India which were constructed by bricks, cement and concrete. This survey is the very first one carried out in this city and constitutes and preliminary survey to check the methodology and to have a first estimation of the indoor radon impact on Dwarka inhabitants. LR-115 type-II, films were used as detector. In the studied dwellings Radon concentration levels were found to vary from 4.4 ± 1.6 to 29.8 ± 3.8 Bqm-3 whereas thoron concentrations is found to vary from 2.8 ± 0.5 to 13.6 ± 1.7 Bqm-3. The annual effective dose from radon were found to vary from 0.12 to 0.86 mSv whereas from thoron found to vary from 0.01 to 0.07 mSv.

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.

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

Conventionally, the dosimetry is carried out using radon and thoron gas concentration measurements and doses have been assigned using assumed equilibrium factors for the progeny species, which is inadequate pertaining to the variations in equilibrium factors and possibly due to significant thoron. In fact, since the true exposures depend upon the intricate mechanisms of progeny deposition in the lung, therefore an integrated approach for the assessment of progeny is essential. In this context, the recently developed deposition based progeny concentration measurement techniques (DTPS: Direct Thoron progeny sensors and DRPS: Direct Radon progeny sensors) appear to be best suited for radiological risk assessments both among occupational workers and general study populations. DTPS and DRPS consist of aluminized mylar mounted LR115 type passive detectors, which essentially detects the alpha particles emitted from the deposited progeny atoms on the detector surface. It gives direct measure of progeny activity concentrations in air. DTPS has a lower limit of detection limit of 0.1 Bq/m(3) whereas that for DRPS is 1 Bq/m(3), hence are perfectly suitable for indoor environments. These DTPS and DRPS can be capped with 200-mesh type wire-screen to measure the coarse fraction of the progeny concentration and the corresponding coarse fraction deposition velocities as well as the time integrated fine fraction. DTPS and DRPS can also be lodged in an integrated sampler wherein the wire-mesh and filter-paper are arranged in an array in flow-mode, to measure the fine and coarse fraction concentration separately and simultaneously. The details are further discussed in the paper.

Radiation dose due to radon, thoron and their decay products in indoor environment of Khurja City, U.P., India

Inhalation of radon, thoron and their decay products can cause a significant health hazard when present in enhanced levels in the indoor environment like a human dwelling. In the present work a set of indoor radon and thoron measurements was carried out using time-integrated passive twin cup dosimeters containing LR-115 Type II solid state nuclear track detectors in different houses of Khurja City in Bulandshahar district of U.P. in India, built of the same type of building materials. The radon gas concentration was found to vary from 9.18 to 23.19 Bq m−3 with an average value of 16.02 Bq m−3 (SD = 3.68) and the thoron gas concentration varied from 2.78 to 9.03 Bq m−3 with an average value of 5.36 Bq m−3 (SD = 1.58). The radon progeny concentration ranged from 0.99 to 2.51 mWL with an average value of 1.77 mWL (SD = 0.40) and the concentration of thoron progeny was found to vary from 0.30 to 0.98 mWL with an average value of 0.58 mWL (SD = 0.17). The annual effective dose varied from 0.27 to 0.67 mSv year−1 with an average value of 0.47 mSv year−1(SD = 0.10).

National survey of indoor thoron concentration in FYR of Macedonia (continental Europe – Balkan region)

As a part of the national survey of natural radioactivity in The Former Yugoslav Republic of Macedonia, indoor thoron gas concentration was measured in 300 dwellings during one year, from December 2008 till December 2009 using passive discriminative radon–thoron detectors. Detectors were deployed at a distance of >50 cm from walls in order to be less sensitive to distance from walls. Altogether 532 measurements were performed: 53 in winter, 57 in spring, 122 in summer and 300 in autumn. The frequency distribution is well described by a log-normal function. The geometric means of indoor thoron concentration (with geometric standard deviations in brackets) in winter, spring, summer and autumn were obtained to be: 39 Bq m−3 (3.4), 32 Bq m−3 (2.8), 18 Bq m−3 (2.8), 31 Bq m−3 (2.9), respectively. Seasonal variations of thoron appear lower than those of radon. The seasonal corrected annual mean concentration ranges between 3 and 272 Bq m−3 with a geometric mean of 28 Bq m−3 (2.12). A detailed statistical analysis of the geogenic and building factors which influence the indoor thoron concentration is also reported. This survey represents the first national survey on indoor thoron in continental Europe.

Long-term measurements of thoron, its airborne progeny and radon in 205 dwellings in Ireland

Long-term (circa 3 months) simultaneous measurements of indoor concentrations of thoron gas, airborne thoron progeny and radon were made using passive alpha track detectors in 205 dwellings in Ireland during the period 2007-09. Thoron progeny concentrations were measured using passive deposition monitors designed at the National Institute of Radiological Sciences (NIRS), Japan, whereas thoron gas concentrations were measured using Raduet detectors (Radosys, Budapest). Radon concentrations were measured in these dwellings by means of NRPB/SSI type alpha track radon detectors as normally used by the Radiological Protection Institute of Ireland (RPII). The concentration of thoron gas ranged from <1 to 174 Bq m(-3) with an arithmetic mean (AM) of 22 Bq m(-3). The concentration of radon gas ranged from 4 to 767 Bq m(-3) with an AM of 75 Bq m(-3). For radon, the estimated annual doses were 0.1 (min), 19.2 (max) and 1.9 (AM) mSv y(-1). The concentration of thoron progeny ranged from <0.1 to 3.8 Bq m(-3) [equilibrium equivalent thoron concentration (EETC)] with an AM of 0.47 Bq m(-3) (EETC). The corresponding estimated annual doses were 2.9 (max) and 0.35 (mean) mSv y(-1). In 14 or 7% of the dwellings, the estimated doses from thoron progeny exceeded those from radon.

Assessment of indoor radiation dose received by the residents of natural high background radiation areas of coastal villages of Kanyakumari district, Tamil Nadu, India

Radiation exposure and effective dose received through two routes of exposure, viz. external and internal, via inhalation, by residents of 10 villages belonging to Natural High Background Radiation Areas (NHBRA) of coastal regions of Kanyakumari District and Tamil Nadu in India were studied. While the indoor gamma radiation levels were monitored using Thermo Luminescent Dosimeters (TLDs), the indoor radon and thoron gas concentrations were measured using twin chamber dosimeters employing Solid State Nuclear Track Detectors (SSNTDs, LR-115-II). The average total annual effective dose was estimated and found to be varying from 2.59 to 8.76 mSv.

Characteristics of thoron and thoron progeny in Canadian homes

Naturally occurring isotopes of radon in indoor air are identified as the second leading cause of lung cancer after tobacco smoking. Radon-222 (radon gas) and radon-220 (thoron gas) are the most common isotopes of radon. While the radon equilibrium factor is well established, the equilibrium factor between thoron progeny and thoron gas is still not well known. Thoron gas and progeny concentrations were determined in the lowest floors of 138 Canadian homes simultaneously. While thoron gas was only detectable in about 52% of the homes, thoron progeny concentrations were measured in every home surveyed. Thoron concentrations, thoron progeny concentrations, and the equilibrium factors varied widely and were log-normally distributed. With a 3 months simultaneous measurement of thoron and thoron progeny concentrations, the equilibrium factor was determined to be 0.024 with a geometric standard deviation of 2.7.

Field Experience with Soil Gas Mapping Using Japanese Passive Radon/Thoron Discriminative Detectors for Comparing High and Low Radiation Areas in Serbia (Balkan Region)

Based on results of fieldwork in the Balkan Region of Serbia from 2005 to 2007, soil gas radon and thoron concentrations as well as gamma dose rates were measured. Campaigns were conducted in two different geological regions: Niska Banja, considered a high natural radiation area, and Obrenovac around the TentB Thermal Power Plant (TPP), a low natural radiation area. Radon and thoron gas measurements were made by using two types of Japanese passive radon/thoron detectors, which included GPS data and gamma dose rates. The concentrations of soil radon gas in Niska Banja ranged from 1.8 to 161.1 kBq m(-3), whereas the concentrations for soil thoron gas ranged from 0.9 to 23.5 kBq m(-3). The gamma dose rates varied from 70 to 320 nGy h(-1). In the TentB area, radon concentration was found to range from 0.8 to 24.9 kBq m(-3) and thoron from 0.6 to 1.9 kBq m(-3). The gamma dose rate ranged from 90 to 130 nGy h(-1). In addition, the natural radioactivity of the soil was investigated at the low background area. The radium and thorium contents in collected soil samples ranged from 23 to 58 and 33 to 67 Bq kg(-1), respectively. As a result of correlation analyses between the measured values, the highest correlation coefficient (R > 0.95) was found for thorium in the soil and the thoron gas concentration.

Equilibrium factor determination using SSNTDs

The proxy equilibrium factor F p was recently proposed by Nikezic et al. [2004. Theoretical basis for long-term measurements of equilibrium factor using LR 115 detector. Appl. Radiat. Isot. 61, 1431–1435] and Yu et al. [2005. Long-term measurements of radon progeny concentrations with solid state nuclear track detectors. Radiat. Meas. 40, 560–568] for long-term passive monitoring of the equilibrium factor F for short-lived 222Rn progeny. In the present paper, we further look into the details for the F p method and study the potential factors affecting the measurements of F using this technique. These factors include (1) the removed active layer of the LR 115 detector, (2) the presence of 220Rn in the ambient environment, and (3) the deposition of dust particles on the LR 115 detector. The corresponding results are: (1) the removed active layer thickness of the LR 115 detector is a very critical parameter in determining F p and hence F ; (2) the presence of thoron in the ambient environment will affect the track densities on the bare LR 115 detector but can be corrected for using the partial sensitivities to thoron; and (3) deposition of dust particles on the bare LR 115 detectors normally will not have significant effects. In addition, a mini-survey of radon and thoron gas concentration and the radon equilibrium factor in different indoor environments has been carried out in different seasons. The conclusion is that the use of an assumed constant F value can result in inaccurate determinations of the effective dose; therefore, actual (long-term) measurements of the F values should be made.

Sensitivity of LR 115 SSNTD in a diffusion chamber

Solid-state nuclear track detectors (SSNTDs), such as LR 115, have been commonly used in diffusion chambers for long-term measurements of radon gas concentrations. For the LR 115 SSNTD, it has been found that the active layer removed during chemical etching is significantly affected by the presence and amount of stirring, and thus cannot be controlled easily. However, the sensitivity of the LR 115 detector inside a diffusion chamber to the radon and/or thoron gas concentration is dependent on the actual removed active layer thickness. This relationship is dependant on the geometry of the diffusion chamber and the deposition fraction of 218Po in the diffusion chamber, as well as the V function for the LR 115 detector (V is the ratio between the track etch velocity Vt to the bulk etch velocity Vb). This paper presents the experimentally determined relationships between the sensitivity of the LR 115 detector inside a Karlsruhe diffusion chamber and the removed active layer thickness, for both radon and thoron. A V function was adjusted to simulate the relationships. In particular, for the case of 222Rn, we have found f∼0.5, where f is the fraction of 218Po which decays inside the diffusion chamber before deposition onto available inner surfaces of the chamber. In conclusion, we have found that the sensitivities critically depend on the actual removed active layer thickness, so this should be monitored and used in determining the sensitivities.