Radon Thoron Research Articles

Radon concentration in spring water as an indicator of seismic activity: a case study of the Muzaffarabad Fault in Pakistan.

Radon and its progenies found in water indicate the existence of seismically active faults in the region. However, exposure to high levels of radon can also result in radiation-related health risks. This study focuses on radon-based active tectonic studies along the Muzaffarabad Fault in the core of the Hazara-Kashmir Syntaxis (HKS), NW Himalayas, Pakistan. In this study, spring water samples were collected along roadside of Jhelum Valley and in close proximity to the Muzaffarabad Fault in Pakistan using Radon Thoron Monitor (RTM1688-2). The results of the study showed that the radon concentrations in the water samples ranged from 1.895 to 17.097 Bq/l. The study found that the highest radon concentration was observed in the samples collected closest to the fault, while the lowest concentration was observed in the samples collected further away. The statistical analysis between the radon concentration and the distance from the fault showed a strong inverse relationship (R2=0.73). The study also found that 68% of the sampling sites had radon concentrations that exceeded the maximum contamination level (MCL) set by the US Environmental Protection Agency (EPA). The higher radon concentrations in the springs water suggest the probability of earthquake, which in turn poses potential health risks for the local population. The findings suggest that the measurement of radon concentration in water can be used as a tool for identifying seismically active faults in the region.

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.

INTERNAL EXPOSURE FROM INDOOR RADON, THORON AND THEIR PROGENY IN RESIDENCE AROUND HIGH BACKGROUND RADIATION AREA, PHANG NGA PROVINCE, THAILAND.

A passive integrating discriminative radon-thoron monitor (Raduet) and a radon-thoron progeny monitor with a solid-state nuclear tracking detector were used for estimating indoor radon, thoron and their progeny concentrations in residential areas around the old mines of southern Thailand. Exposure to high background radiation levels from natural 238U and 232Th in the tin mine areas or active fault areas may increase the risk of lung cancer in the respiratory system when considering the health effects of the surrounding inhabitants. In this study, radon thoron and their progeny concentrations from inhalation in the study site have been assessed in dose at volunteer houses to confirm radiation effects. The annual effective doses due to inhalation of radon-thoron, radon progeny and thoron progeny using the ICRP latest dose conversion factors were estimated to be 3.0-4.6, 2.5-3.7 and 0.4-1.0mSv, respectively, and as 5.9-9.0mSv in total.

Estimation of Radon Thoron Levels in Jind Area of Haryana

Health risk estimations due to the indoor exposure to natural radionuclides present in natural radioactive gases like radon and thoron the is a cause of concern. The main radiation exposure of the inhabitants of dwellings is due to the two radioactive gases viz. radon and thoron. These gases can accumulate inside the rooms/indoor places of dwellings depending on various parameters like emanation from soil, ventilation, type of dwelling and construction materials, etc. However, the knowledge of concentration of these gases is required to safeguard the dwellers from its health hazardous, if these increases beyond a certain level. In this paper, a study has been conducted in some of the dwellings of the Jind area of Haryana state for the estimation of indoor radon thoron levels. Some 25 dwellings were selected in a uniform manner to cover the whole area of Jind. The found results were assessed on the basis of International Commission on Radiological Protection (ICRP) guidelines.

Monitoring of natural radionuclides by alpha scintillometry and gamma spectrometry techniques in soil of district Palwal, Southern Haryana, India

ABSTRACT Forty soil samples from district Palwal of Southern Haryana, India were collected to estimates the radon/thoron exhalation rate using scintillation detector-based SMART RnDuo out of which twenty samples were tested to estimate the activity of 226Ra, 232Th and 40K using high purity germanium (HPGe) gamma-ray spectrometry. The radon mass exhalation rate (mBqkg−1h−1) was observed as {range (mean)} {16 ± 1–48 ± 3 (28 ± 8)} and thoron surface exhalation rate (Bqm−2h−1) was observed as {1800 ± 198–6331 ± 205 (3850 ± 850)}. Activities of radium (226Ra), thorium (232Th) and potassium (40K) were {range (mean)} observed as {28.4–48.4 (40.0 ± 1.4)}, {49.7–75.0 (62.7 ± 1.6)} and {432–698 (522.9 ± 17.6)}, respectively. It is observed that the radium in 75% samples while thorium and potassium in all samples were found to higher than the world’s average values of 35, 30 and 400 Bqkg−1, respectively, as reported by UNSCEAR. Average of radon mass exhalation and thoron surface exhalation rates exceeded the world’s mean value 57 mBq kg−1 h−1 and 3600 Bq m−2 h−1, respectively. Health hazard index is well below the unity (< 1), which indicates that there are no gamma radiation hazards associated with samples collected from the study region.

Characterization of Commercially Available Active-Type Radon–Thoron Monitors at Different Sampling Flow Rates

Recently, some commercially available active-type radon–thoron monitors were developed; however, their performance has not been characterized. This article presents the characteristics of three commercially available active-type radon–thoron monitors (RAD7, Radon Mapper, and AlphaGUARD) at different sampling flow rates. The thoron concentration measured by the monitors was compared with the reference value measured by a grab sampling method. As a result, the ratio of the measured concentration to the reference increased with flow rate for the RAD7 and the Radon Mapper although that of the AlphaGUARD decreased. The difference may be attributed to the coefficients used in the calculation and the measurement time scheme. The results indicate the importance of the sampling flow rate in thoron measurement. Monitoring of flow rate at the measurement and periodic calibration at multiple sampling flow rates should be conducted for quality assurance and quality control of the measurand.

ASSESSMENT OF RADON AND THORON EXHALATION FROM SOILS AND DISSOLVED RADON IN GROUND WATER IN THE VICINITY OF ELEVATED GRANITIC HILL, CHIKKABALLAPUR DISTRICT, KARNATAKA, INDIA

In this paper, we intend to evaluate the rate of radon and thoron exhalation from soil with reference to the underlying bedrock and gamma dose rate in the environment of elevated granitic hill-Nandi hills of Karnataka. The measurement of exhalation rates for all the soil samples collected from study area was carried out using a continuous radon-thoron monitor (Smart RnDuo monitor). The surface exhalation rate of thoron from soil samples were found to vary from 4160±326 to 21822±634 mBq m-2s-1. The mass exhalation rate of radon from soil samples were found to vary from 76±6 to 269±19 mBq kg-1h-1. Concentrations of radon activity measurements were carried out for all the groundwater samples from study area. A detailed analysis along with physicochemical parameters of water has been made and discussed in this research paper.

Importance of Discriminative Measurement for Radon Isotopes and Its Utilization in the Environment and Lessons Learned from Using the RADUET Monitor.

Radon (222Rn) and thoron (220Rn), sources of natural background radiation, have been the subjects of long-standing studies, including research into radon and thoron as major causes of lung cancer at domestic and international levels. In this regard, radon and thoron measurement studies have been widely conducted all over the world. Generally, the techniques used relate to passive nuclear track detectors. Some surveys have shown that passive monitors for radon are sensitive to thoron, and hence some measured results have probably overestimated radon concentrations. This study investigated radon and thoron measurements in domestic and international surveys using the passive radon–thoron discriminative monitor, commercially named RADUET. This paper attempts to provide an understanding of discriminative measurements of radon isotopes and to present an evidence-based roadmap.

Variable Strength in Thoron Interference for a Diffusion-Type Radon Monitor Depending on Ventilation of the Outer Air

Thoron interference in radon measurements using passive diffusion radon detectors/monitors is a crucial problem when it comes to assessing the internal exposure to radon precisely. The present study reported, as one of the potential factors, the effects of air flow conditions on changes in thoron interference. Rates of thoron infiltration (as thoron interference) into the diffusion chamber of the monitor were evaluated. The temporal variation was obtained based on measurements of the underfloor space of a Japanese wooden dwelling using a diffusion-type radon monitor, a reference radon monitor which was not affected by thoron interference, and a thoron monitor. The thoron infiltration rate for the diffusion-type monitor varied from 0% to 20%. In particular, it appeared to increase when ventilation of the underfloor space air was forced. The variable thoron infiltration rate, with respect to ventilation strength, implied that not only a diffusive process, but also an advective process, played a major role in air exchange between the diffusion chamber of the monitor and the outer air. When an exposure room is characterized by the frequent variation in air ventilation, a variable thoron response is considered to occur in radon–thoron discriminative detectors, in which only diffusive entry is employed as a mechanism for the discrimination of radon and thoron.

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.

Natural radiation exposure to the public in the uranium bearing region of Poli, Cameroon: From radioactivity measurements to external and inhalation dose assessment

The present work reports measurements of activity concentrations of 238U, 232Th, and 40K in soil, 222Rn and 220Rn in dwellings, and air kerma rates followed by external and inhalation dose assessment to the public in the uranium bearing region of Poli. These measurements were carried out using a 3-in × 3-in NaI(Tl) scintillation spectrometer for radioactivity in soil, car-borne survey method for air kerma rates, and Passive integrated radon–thoron discriminative detectors (RADUET) and thoron progeny monitors for radon, thoron, and thoron progeny indoors respectively. In-situ activity concentrations of 238U, 232Th, and 40K range between 13–52 Bq kg−1, 10–67 Bq kg−1, and 242–777 Bq kg−1 respectively with respective average values of 32 Bq kg−1, 31 Bq kg−1, and 510 Bq kg−1. Air kerma rates range between 25 and 102 nGy h−1 with the mean value of 57 nGy h−1. The annual effective doses due to public external exposure range between 0.20 and 0.83 mSv y−1 with the mean value of 0.46 mSv y−1. Taking into account of the number of inhabitants and the level of external dose, some inhabited areas were selected for radon, thoron and thoron progeny measurements in 100 houses. Radon and thoron concentrations range between 46–137 Bq.m−3 and 24–238 Bq.m−3 with the arithmetic mean values of 82 Bq m−3 and 94 Bq m−3 respectively. The equilibrium equivalent thoron concentrations (EETC) and the equilibrium factor for thoron range respectively between 4–29.6 Bq m−3 and 0.008–0.3 with the average values of 8.3 Bq m−3 and 0.08. The equilibrium factor found to be higher than the world average value of 0.02 given by the United Nations Scientific Committee on Effects of Atomic Radiation (UNSCEAR). The inhalation doses due to radon progeny and thoron progeny range between 0.87–2.6 mSv y−1 and 0.34–6.2 mSv y−1 respectively. The contribution of thoron to the total inhalation dose ranges between 12–67% with the average value of 49%, showing that thoron cannot be neglected in dose assessment as done in the past.

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.

Estimating excess of lung risk factor of radon gas for some houses in Al-Fallujah city

Instruments for the measurements of radon, thoron and its decayproducts in air are based mostly on the detection of alpha particles.The health hazards of radon on general public are well known. Inorder to understand the level and distribution of 222Rn concentrationsindoor in Al-Fallujah City; new technique was used, this techniquewas three radon–thoron mixed field dosimeters is made up of a twinchamber cylindrical system and three LR-115 type II detectors wereemployed. The aim of this work was to measurement radon gas usingSSNTD technique door in in Al-Fallujah City, and estimation ofexcess in cancer due to increment in radon gas. Results for sampleswhich are collected from January to April 2013 show that the 222Rnconcentration varies from 52.33 to 108.70 Bq.m-3 with an average of84.64 Bq.m-3, according to EPA and ICRP, the average indoor radonlevel should be 148 Bq/m3 and 300 Bq/m3, respectively, whereasapproximately 15 Bq/m3 (ranging from 1 Bq/m3 to 100 Bq/m3 ofradon concentration is normally found in outside air. Also the valuesof annual effective dose and excess lung cancer per million peopleper year (ELC) have also been calculated and found to vary from0.941 to 2.350 mSv.y-1 with an overall average of 1.581 mSv.y-1 and,565 to 1410 with an overall average 948, respectively.

Seasonal variation of indoor radon–thoron levels in dwellings of four districts of Haryana, India

In the present work, seasonal (winter, rainy, summer) variation of indoor radon and thoron was measured for 120 days from 91 dwellings in different villages and towns in four districts (Rohtak, Sonipat, Panipat, and Jind) of Haryana using single-entry pinhole-based radon–thoron-discriminating dosimeters. The present study is imperative because a thermal power plant is present in Panipat district, and the Yamuna River passes through the Sonipat and Rohtak districts, and a high-heat-producing granite (HHPG) region is in the vicinity of the study area. Annual effective dose due to radon and thoron has been calculated by using an equilibrium factor as determined by other studies in the neighboring region. Concentrations for one year were estimated (March 2015–February 2016) from data collected for 4 months. The result shows that the annual indoor radon levels vary from 9.12 ± 1.14 to 94.23 ± 9.94 Bq/m3 with an average value of 21.66 ± 3.08 Bq/m3. The annual indoor thoron levels vary from 15.18 ± 2.85 to 105.35 ± 15.17 Bq/m3 with an average value of 52.82 ± 7.15 Bq/m3. The annual effective dose varies from 0.85 to 4.73 mSv with an average value of 2.41 mSv. The average value of annual indoor radon and thoron is lower than the limits of 100 Bq/m3 as recommended by the World Health Organization and the thoron value is higher than the worldwide average value of 40 Bq/m3. Indoor radon and thoron concentrations are highest in the winter and lowest in the summer. Concentrations of these gases in the rainy season are higher compared to the summer season. When we compare the rainy and winter seasons, concentrations of these gases are higher in the winter season. The differences in average concentrations of radon and thoron values are presented by the ratio of average radon and thoron concentrations in three seasons. Hence, the winter–summer ratio, winter–rainy season ratio, and rainy season–summer ratio of average radon concentrations in the study region are 1.72, 1.41, and 1.50, respectively. For the thoron concentration, winter–summer ratio, winter–rainy season ratio, and rainy season–summer ratio are 1.38, 1.05, and 1.38, respectively. This study area is safe from radiological effects of radon and thoron gases in confined spaces because the annual effective dose is lower than established safe limits.

Study of radon/thoron exhalation rate, soil-gas radon concentration, and assessment of indoor radon/thoron concentration in Siwalik Himalayas of Jammu & Kashmir

ABSTRACTIn the present study, the soil-gas radon concentration was assessed at different depth intervals, i.e., 15 cm, 30 cm, 60 cm, and 100 cm from the 30 villages of Jammu & Kashmir, India using RAD7, an electrostatic solid state alpha detector. The radon mass exhalation and thoron surface exhalation rate has also been measured in the selected 18 soil samples out of 30 of different grain sizes (i.e., 1 mm, 300 µm, 150 µm). The active radon and thoron concentrations were also assessed in the 20 villages. Both the exhalation rates and active radon/thoron concentration were measured using SMART Rn Duo, a portable radon monitor. The average values of soil-gas radon concentration were 210 ± 84 Bq m−3, 1261 ± 963 Bq m−3, 4210 ± 1994 Bq m−3, and 671 ± 305 Bq m−3 at the depth intervals of 15 cm, 30 cm, 60 cm, and 100 cm, respectively. The exhalation rate of radon and thoron from soil was found to decrease with the increase of grain size, as smaller soil particles make relatively more contribution to radon and thoron exhalations from the ground surface than larger soil particles. The measured Pearson's correlation coefficient was obtained as statistically significant between different quantities under two-tailed test.

Study on Radon and Thoron Levels in and Around Different Industries of Tumkur and Bangalore Districts

Radon, Thoron and their progenies were estimated in and around the industrial area of Tumkur and Bangalore rural district by using Solid State Nuclear Track Detector (SSNTD) method. In this study the rice mills, paint industries, bio fuels, tyre recycling industries, granite industries, stone crushing industries, brick industries, oil seed industries, and garments are selected for indoor radon thoron measurements. The study shows that the concentration of radon and thoron are widely varies and also depends on the industrial activity and type of construction of industry. The study shows that the concentration of radon varies from 35.51 ± 1.31 to 245.36 ± 1.21 Bqm-3 with an average value of 115.31 Bqm-3 and thoron varies from 25.95 ± 2.36to 312.72 ± 1.58 Bqm-3 with an average value of 110.44 Bqm-3. The average radon concentrations are less than the lower limit of the action levels (200-300 Bqm-3) as recommended by ICRP. The corresponding progeny level of radon varies from 0.24 to 13 mWL and thoron progeny varies from 0.11 to 11 mWL. The annual effective doses received by the industrial workers are slightly lower than the recommended action level (3-10 mSvy-1).

TESTING OF INDIVIDUAL SENSITIVITY TO RADON AND THORON EXPOSURE BY IN VITRO IRRADIATION OF LYMPHOCYTES CULTURE

Identify the factors that affect individual sensitivity is a very important step in cancer risk assessment at low doses or low doses rates, according with study of dose-response relationship. DNA damage response processes are likely to play an important role in radiation by cancer risk association. This paper tries to quantify the individual sensitivity to alpha particles exposure using an in vitro exposure model. Quantify of DNA lesions by comet assay, in lymphocytes cultures exposed to the same doses of radiation was made. The irradiation was performed using the pitchblende ore during a 72 hours period, intermittent exposure with dose rates of 89.15 kBq/m3. The lowest and highest Radon Thoron concentrations computed in this study were 89.15 kBq/m3 and 212.9 kBq/m3, respectively. The study was done for healthy donors, comparatively with chronic obstructive pulmonary diseases donors. Ageing in vitro of lymphocytes cultures exposed to low doses of ionizing radiation is the biological model used, which are presented here. Based on these results, a standard test should be develop and applied for study of sensitivities in average population groups.

Radionuclide measurements along with exhalation study in subsoil of southeast Haryana, India

A comprehensive gamma-ray spectrometry study was conducted to determine thorium, uranium and potassium elemental concentrations in soil samples in the southeast region of Haryana. The collected soil samples were air-dried, sieved through a fine mesh, sealed in 300-ml plastic container and analyzed in the laboratory for their gamma radioactivity using NaI(Tl) gamma spectrometer. From measured gamma-ray spectra, activity concentration was observed for 238U (1.6 ± 0.32–23.3 ± 7.7 Bq kg−1), 232Th (21.9 ± 5.4–157.2 ± 6.5 Bq kg−1) and 40K (228 ± 14–389 ± 16 Bq kg−1). The annual effective dose and absorbed dose rates have been calculated with different fractional utilization of building material in dwellings. Same samples have been analyzed for radon mass and thoron surface exhalation study using scintillation radon and scintillation thoron monitor to find out the correlation between the various radionuclides present in the vicinity, and the results found in good agreement with the observed elemental activity in the exhalation study.

MEASUREMENT OF RADON CONCENTRATION IN DWELLINGS IN THE REGION OF HIGHEST LUNG CANCER INCIDENCE IN INDIA

Indoor radon/thoron concentration has been measured in Aizawl district, Mizoram, India, which has the highest lung cancer incidence rates among males and females in India. Simultaneously, radon flux emanated from the surrounding soil of the dwellings was observed in selected places. The annual average value of concentration of radon(thoron) of Aizawl district is 48.8(22.65) Bq m-3 with a geometric standard deviation of 1.25(1.58). Measured radon flux from the soil has an average value of 22.6 mBq m-2 s-1 These results were found to be much below the harmful effect or action level as indicated by the World Health Organisation. On the other hand, food habit and high-level consumption of tobacco and its products in the district have been found to increase the risk of lung cancer incidence in the district.

Monitoring of radon, thoron, their progeny concentrations in dwellings, and radon exhalation rates of soil/sand of Rupnagar district, Punjab, India

Radon and its progeny are major contributors in the radiation dose received by general population of the world. Keeping this in mind, the environmental monitoring of radon–thoron and their progeny in dwellings of district Rupnagar, Punjab, India has been carried out. Both radon–thoron twin dosimeter cups and the newly developed pin-hole dosimeters cups by BARC, India were used for the study. The study reveals good agreement between the values measured by the two types of dosimeters. Radon exhalation rate from soil samples of these dwellings/areas have been carried out using “Canister Technique.” The radon exhalation rates of some soil samples of these dwellings/areas were also measured by an active technique using a continuous radon monitor. Both the active and passive techniques show the exhalation rate values to be lower than the worldwide average. The study of the exhalation rate of the soil samples of Nangal and Anandpur Sahib of the district Rupnagar and the sand samples available from the study area has also been carried out for the possible use as construction material. The in situ gamma dose varied from 0.13 to 0.33 µSv/h.