Uranium, radium and radon exhalation studies in some soil samples using plastic track detectors

Radium concentration and radon exhalation rate have been measured in soil samples collected from some areas belonging to upper Siwaliks of Kala Amb, Nahan and Morni Hills of Haryana and Himachal Pradesh states, India using LR-115 type II plastic track detectors. Uranium concentration has also been determined in these soil samples using fission track registration technique. Radium concentration has been found to vary from 5.30 to 31.71 Bq.kg⁻¹, whereas uranium concentration varies from 33.21 to 76.26 Bq.kg⁻¹. The radon exhalation rate in these samples varies from 216.87 to 1298.00 mBq.m⁻²hr⁻¹ (6.15 to 36.80 mBq.kg⁻¹.hr⁻¹). Most of the samples have uranium concentration above the worldwide average concentration of 35 Bq.kg⁻¹. A good correlation (R ² = 0.76) has been observed between uranium concentration and radon exhalation rate in soil. The values of uranium, radium and radon exhalation rate in soil are compared with that from the adjoining areas of Punjab.     

Radon exhalation rate in Chhatrapur beach sand samples of high background radiation area and estimation of its radiological implications

Chhatrapur beach placer deposit, situated in a part of the eastern coast of Orissa, is a newly discovered high natural background radiation area (HBRA) in India. The sand samples containing heavy minerals, were collected from Chhatrapur region by the grab sampling method at an interval of ∼1 Km. Radon exhalation rates were measured by “Sealed Can Technique” using LR-115 type type II in the sand samples containing heavy minerals collected from the beach. Radon activity is found to vary from 1177.1 to 4551.4 Bq m-3 whereas the radon exhalation rate varies from 423.2 to 1636.3 mBq m⁻²h⁻¹ with an average value of 763.9 mBq m⁻²h⁻¹. Effective dose equivalent in sand samples estimated from exhalation rate varies from 49.9 to 193.0 μSv y⁻¹ with an average value of 90.1 μSv y⁻¹. From the activity concentration of ²³⁸U, ²³²Th and ⁴⁰K computed radium equivalent is found to vary from 864.0 to 11471.5 Bq kg⁻¹ with an average value of 3729.0 Bq kg⁻¹. External hazard index, H_ex range from 2.3 to 31.0 with a mean value of 10.1, which is quite high. This value supports the conclusion based on high mean absorbed gamma dose rate in air due to the naturally occurring radionuclides as 1627.5 nGy h⁻¹. A positive correlation has been found between U concentration and radon exhalation rate in the sand samples. The use of sand as construction material may pose a radiation risk to ambient environment.      

Radon in soil and its concentration in the atmosphere around Mysore city, India

Radon concentration in soil-gas and in the atmospheric air has been studied around Mysore city (12°N and 76°E) using Solid State Nuclear Track Detectors. The radon in soil-gas is found to be higher at a depth of 1 m than at a depth of 0.5 m from the ground surface. The higher radon concentration in soil was observed near Chamundi Hills and Karigatta village with average values of 5.94 kBq.m⁻³ and 5.32 kBq.m⁻³ at 1 m depth from the ground surface. Seasonal variations in radon in soil gas shows that, the concentration is lower in summer with an average value of 0.60 kBq.m⁻³ and higher in monsoon season with an average value of 4.70 kBq.m⁻³. Estimation of ²²⁶Ra in soil at these locations is also made using HPGe detector. The activity of ²²⁶Ra, varies from 4.82 to 74.23 Bq.kg⁻¹ with an average value of 32.11 Bq.kg⁻¹. Radon concentrations in soil-gas shows good correlation with the activity of ²²⁶Ra in soil with a correlation coefficient of 0.76     

Radon exhalation studies in building materials using solid-state nuclear track detectors

Indoor radon has been recognized as one of the health hazards for mankind. Building materials constitute the second most important source of radon in dwellings. The common building materials used in the construction of dwellings are studied for radon exhalation rate. The ‘Can’ technique using LR-115 type-II solid-state nuclear track detector has been used for these measurements. The radon exhalation rate in these samples varies from 4.75 m Bq m⁻² h⁻¹ (0.14 m Bq kg⁻¹ h⁻¹) for limestone to 506.76 m Bq m⁻² h⁻¹ (15.24 m Bq kg⁻¹ h⁻¹) for soil.     

Seasonal variation of radon level and radon effective doses in the Catacomb of Kom EI-Shuqafa,Alexandria, Egypt

Inhalation of radon has been recognized as a health hazard. In the present work radon concentration was measured, in the atmosphere of the archaeological place, namely Catacomb of Kom El-Shuqafa, in Alexandria, Egypt, which is open to the public, using time-integrated passive radon dosimeters containing LR-115 solid-state nuclear track detector. The measurements were performed throughout winter and summer. Seasonal variation of radon concentration, with the maximum in summer ranging from 243 to 574 Bq m^− 3 and minimum in winter ranging from 64 to 255 Bq m^− 3 was observed. Because of the variations of the catacomb ventilation system, the equilibrium factor between radon and its progeny ranges from 0.14 to 0.48. The tour guides are exposed to an average estimated annual effective dose ranging from 0.21 to 0.52 mSv y^− 1 and the visitors from 0.88 to 2.28 μSv y^− 1. The effective doses the catacomb workers are exposed to ranged from 0.20 mSv y^− 1 in winter to 4.65 mSv y^− 1 in summer which exceeds the lower bound of the recommended level (3–10 mSv y^− 1) (ICRP, 1993).     

Analysis of 226Ra, 232Th and 40K in soil samples for the assessment of the average effective dose

The activity concentrations of the natural radionuclides namely ²³⁸Ra, ²³²Th and ⁴⁰K are measured for soil samples collected from different locations of Faridkot and Mansa districts of Punjab. HPGe detector, based on high-resolution gamma spectrometry system is used for the measurement of activity concentration. The range of activity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K in the soil from the studied areas varies from 21.42 Bq kg⁻¹ to 40.23 Bq kg⁻¹, 61.01 Bq kg⁻¹ to 142.34 Bq kg⁻¹ and 227.11 Bq kg⁻¹ to 357.13 Bq kg⁻¹ with overall mean values of 27.17 Bq kg⁻¹, 95.22 Bq kg⁻¹ and 312.76 Bq kg⁻¹, respectively. Radium equivalent activities are calculated for the analyzed samples to assess the radiation hazards arising due to the use of these soil samples in the construction of dwellings. The absorbed dose rate calculated from activity concentration of ²²⁶Ra, ²³²Th and ⁴⁰K ranges between 9.87 and 18.55, 38.01 and 88.68 and 9.40 and 14.79 nGy h⁻¹, respectively. The total absorbed dose in the study area ranges from 61.10 nGy h⁻¹ to 112.86 nGy h⁻¹ with an average value of 84.80 nGy h⁻¹. The calculated values of external hazard index (H _ex) for the soil samples of the study area range from 0.36 to 0.68. Since these values are lower than unity, according to the Radiation Protection 112 (European Commission, 1999) report, soil from these regions is safe and can be used as construction material without posing any significant radiological threat to population. The corresponding average annual effective dose for indoor and outdoor measured in the study area are 0.42 mSv and 0.10 mSv respectively.      

In situ measurements of radon levels in water and soil and exhalation rate in areas of Malwa belt of Punjab (India)

Radon concentration levels in water and soil gas from 36 locations pertaining to some areas of Malwa region of Punjab have been measured on an in situ basis using a continuous active radon detector (AlphaGuard, Model – PQ 2000 PRO, Genitron instruments, Germany). Exhalation rate measurements have also been carried out at these places, using a closed-circuit technique. The radon concentrations in soil and water varied from 1.9 to 16.4 kBq m^?3 and 5.01 to 11.6 kBq m^?3, respectively. The exhalation rate (E _Rn) ranged between 7.48 and 35.88 mBq m^?2 s^?1 with an average value of 18.17 mBq m^?2 s^?1. Annual dose rates have been calculated for water radon concentrations. The minimum to maximum values of dose rates were found to be 13.42–31.08 μSv y^?1. The recorded values of radon concentration in water are within the safe limit of 11 Bq l^?1 recommended by the US Environment Protection Agency [National Research Council, Risk Assessment of Radon in Drinking Water (Academy Press, Washington, DC, USA, 1999)]. All measurements were made in similar climatic and environmental conditions to ensure minimal variations in meteorological parameters. An intermediate correlation coefficient (0.5) was observed between radon exhalation rates and soil gas values.     

Measuring radon exhalation rate by tracing the radon concentration of ventilation-type accumulation chamber

Radon exhalation rate is crucial in the estimation of radiation risk from various materials. RAD7 only focus on the count of the ²¹⁸Po in sniff mode, and is well suited to measure radon exhalation rates. This paper presents a fast method for measuring radon exhalation from medium surface with a ventilation-type accumulation chamber by the RAD7 while making the effects of leakage and back diffusion negligible. The radon exhalation rate can be obtained from the measured values before radioactive equilibrium between Radon and progeny occurs. This method is based on the principle for tracing radon concentration changes by deriving ²²²Rn concentrations through ²¹⁸Po measurements. Several radon exhalation rate measurements of medium surface have been performed in the Radon Laboratory of the University of South China. The radon exhalation rates obtained by verification experiments are within the accepted values for the reference value.     

Indoor radon monitoring in some buildings surrounding the national Hydroelectric Power Corporation (NHPC) project at upper Siang in Arunachal Pradesh, India

In the present study measurement of radon and its progeny concentration has been undertaken in the buildings constructed in the surroundings of National Hydroelectric Power Corporation (NHPC). LR-115 Type-II solid state nuclear track detectors fixed on a thick flat card were exposed in bare mode. Track etch technique has been used to estimate the radon concentration in the rooms of some buildings. Annual effective dose has been calculated from the radon concentration to carry out the assessment of the variability of expected radon exposure of the population due to radon and its progeny. The radon levels in these dwellings vary from 9±4 to 472±28 Bq m⁻³ with an average value of 158±14.9 Bq m⁻³ whereas annual effective dose varies from 0.1±0.04 to 7±0.4 mSv y⁻¹ with an average value of 2.3±0.2 mSv y⁻¹. These values are below the recommended action levels.     

Field Measurements of Radon Exhalation and Ra-226 Content in Soil using the Can-Technique

CR-39 and LR-115 plastic nuclear track detectors in the can-technique have been employed in the field measurements of radon exhalation, Ra-226 and U-238 content in dry-soil air at numerous regions in Sudan (the Blue and White Nile and Mogran regions). Measurements gave an average radon exhalation from the soil to the atmosphere and Ra-226 content of (23.4 ± 2.60) kBq · m^?2 and (123 ± 13.65) Bq · kg^?1 respectively. A polyethylene permeable membrane cover was used to eliminate the contribution of thoron activity inside the can. Assuming a radioactive equilibrium between the U-series, the average U-238 content in the soil was found to be (9.92 ± 1.01) ppm. This survey may be used for uranium prospection in soil.     

Radon exhalation and gamma radioactivity levels in soil and radiation hazard assessment in the surrounding area of National Thermal Power Corporation,Dadri (U.P.), India

In the present study soil samples were collected from the region around a National Thermal Power Corporation (NTPC) at Dadri (U.P.), India. Radon activity and radon exhalation rates were measured by using “sealed can technique” using LR 115-type II nuclear track detectors. Radon activities are found to vary from 177.5 ± 23.1 to 583.4 ± 4.9 Bq m⁻³ with an average value of 330.5 ± 30.4 Bq m⁻³. Surface exhalation rates in these samples vary from 63.9 ± 8.3 to 210.2 ± 15.1 mBq m⁻² h⁻¹ with an average value of 119.1 ± 11.1 mBq m⁻² h⁻¹, whereas mass exhalation rates vary from 2.5 ± 0.3 to 8.1 ± 0.6 mBq kg⁻¹ h⁻¹ with an average of 4.6 ± 0.4 mBq kg⁻¹ h⁻¹.Activity concentrations of naturally occurring radionuclides (²²⁶Ra, ²³²Th and ⁴⁰K) were also measured in these soil samples using high resolution γ–ray spectroscopic system. Activity concentrations of ²²⁶Ra, ²³²Th, and ⁴⁰K vary from 32.2 ± 6.0 to120.9 ± 4.5 Bq kg⁻¹, 19.3 ± 0.9 to 44.6 ± 1.5 Bq kg⁻¹ and 195.4 ± 2.8 to 505.4 ± 6.3 Bq kg⁻¹ with overall mean values of 70.0 ± 8.9 Bq kg⁻¹, 34.8 ± 1.2 Bq kg⁻¹ and 436.1 ± 5.6 Bq kg⁻¹ respectively. From the activity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K, radium equivalent activity (Ra_eq) and the external hazard index (H_ex) were calculated and found to vary from 73.4 to 214.7 Bq kg⁻¹ and from 0.2 to 0.6 respectively.     

In situ measurements of radon levels in water and soil and exhalation rate in areas of Malwa belt of Punjab (India)

Radon concentration levels in water and soil gas from 36 locations pertaining to some areas of Malwa region of Punjab have been measured on an in situ basis using a continuous active radon detector (AlphaGuard, Model - PQ 2000 PRO, Genitron instruments, Germany). Exhalation rate measurements have also been carried out at these places, using a closed-circuit technique. The radon concentrations in soil and water varied from 1.9 to 16.4?kBq?m(-3) and 5.01 to 11.6?kBq?m(-3), respectively. The exhalation rate (E (Rn)) ranged between 7.48 and 35.88?mBq?m(-2)?s(-1) with an average value of 18.17?mBq?m(-2)?s(-1). Annual dose rates have been calculated for water radon concentrations. The minimum to maximum values of dose rates were found to be 13.42-31.08?μSv?y(-1). The recorded values of radon concentration in water are within the safe limit of 11?Bq?l(-1) recommended by the US Environment Protection Agency [National Research Council, Risk Assessment of Radon in Drinking Water (Academy Press, Washington, DC, USA, 1999)]. All measurements were made in similar climatic and environmental conditions to ensure minimal variations in meteorological parameters. An intermediate correlation coefficient (0.5) was observed between radon exhalation rates and soil gas values.     

Correlations between radon in soil gas and the activity of seismogenic faults in the Tangshan area,North China

The spatial variation of soil gas radon values were correlated with the seismogenic faults and earthquakes in the Tangshan area (north China). Radon concentrations were measured at 756 sites in an area about 2500 km² from April to May 2010. The background and anomaly threshold values calculated were 4730.4 Bq/m³ and 8294.1 Bq/m³, respectively. Radon concentrations highlight a decreasing gradient from NE to SW in the area. Higher values mostly distributed in the NE sector of the Tangshan fault and the Luanxian fault where the Tangshan (Ms 7.8), and Luanxian (MS 7.1) earthquakes occurred in 1976 and 17 earthquakes with MS = 3.0 occurred in this area since 2005. Radon values illustrated a close relation with the shallow fault trace and earthquake activity in the area. The active fault zones and the associated fractures formed by the larger earthquakes, act as paths for radon migration.     

Study of radon transport through concrete modified with silica fume

The concentration of radon in soil usually varies between a few kBq/m³ and tens or hundreds of kBq/m³ depending upon the geographical region. This causes the transport of radon from the soil to indoor environments by diffusion and advection through the pore space of concrete. To reduce indoor radon levels, the use of concrete with low porosity and a low radon diffusion coefficient is recommended. A method of reducing the radon diffusion coefficient through concrete and hence the indoor radon concentration by using silica fume to replace an optimum level of cement was studied. The diffusion coefficient of the concrete was reduced from (1.63 ± 0.3) × 10⁻⁷ to (0.65 ± 0.01) × 10⁻⁸ m²/s using 30% substitution of cement with silica fume. The compressive strength of the concrete increased as the silica-fume content increased, while radon exhalation rate and porosity of the concrete decreased. This study suggests a cost-effective method of reducing indoor radon levels.     

The use of soil gas as radon source in radon chambers

A procedure is described in which soil gas is utilized as an alternative to the ²²⁶Ra source for the supply of the radon gas required to fill a radon chamber where radon-measuring devices are calibrated. The procedure offers opportunities to vary the radon concentration within the chamber around an average value of about 500 Bq/m³, which is considered to be sufficient for calibrating indoor radon detectors. The procedure is simple and the radon source does not require radiation protection certification (for import and/or use), unlike the commercially produced standard radioactive (²²⁶Ra) sources.     

Fast determination of uranium and radium in waters of variable composition

The effects of uranium and its progeny radium are known to be harmful and their measurements in drinking water are necessary for careful monitoring. Fast and accurate methods for determination of uranium and radium in water samples with various salinity and activities concentrations have been developed. High Resolution Inductively Coupled Plasma Mass Spectrometry is used for direct measurement of uranium. Calibration is performed with ²³⁸U standards and ²⁰⁹Bi is used as internal standard to correct the matrix effects and plasma instability. The radium is determined by photon electron rejected alpha liquid spectrometry after a chemical separation procedure that includes co-precipitation of radium with barium sulphate, transformation of the sulphate to carbonate and extraction of radium in the scintillation cocktail. The minimal detectable activities of 3.5×10⁻⁸ Bq kg⁻¹ for uranium and 2.3×10⁻⁴ Bq kg⁻¹ for radium are obtained.     

Indoor radon survey in Eastern Sicily

Inhalation of radon (Rn-222) and its progeny is one of the most significant sources of natural radiation exposure of the population. Nowadays, high radon exposures have been shown to cause lung cancer and many governments all over the world have therefore recommended that radon exposures in dwellings and indoor workplaces should be limited. Radon levels in buildings vary widely from area to area depending on local geology. This paper presents the results of a long-term survey of radon concentrations carried out from 2005 till 2010 in schools and dwellings of Eastern Sicily, using the solid-state nuclear track detector (SSNTD) technique. The investigated area shows medium-high indoor radon concentrations, higher than the Italian average of about 70 Bq/m³, with peaks of 500 Bq/m³ or more in buildings near active faults. Fortunately, only a small fraction of the measurements, about 1.5% of total, was found greater than EU and Italian action limits for indoor and workplaces.     

A comparative study of indoor radon levels and inhalation dose in some areas of Punjab and Haryana, India

Indoor radon concentrations have been measured for two consecutive half-year periods in a wide range of dwellings of some regions of Punjab and Haryana states. The objective was to find correlation between the variations of indoor radon levels with the sub-soil, local geology, type of building materials, etc. of the two regions. So keeping this in view the indoor radon measurements have been carried out in the dwellings of different villages around the Tusham ring complex, Bhiwani District, Haryana, known to be composed of acidic volcanics and the associated granites along with some villages of Amritsar District, Punjab. The indoor radon concentration in the dwellings around Tusham (Haryana) have been found to be varying from 120.5±95 to 915.2±233 Bq m⁻³, whereas it ranges from 60.0±37 to 235.6±96 Bq m⁻³ for the dwellings of Punjab. The ²²²Rn concentration observed at most of locations particularly around Tusham ring complex region is higher than that of all the villages studied in Punjab region. Local geology including embedded granitic rocks, sub-soil, etc. as well as building materials having higher radioactive content are the major contributors for the higher indoor radon levels observed in the dwelling around Tusham, where few dwellings have higher radon concentrations than the ICRP, 1993 recommendations. The annual effective dose equivalent has also been estimated for each location of the both regions, which has been found to be varying from 1.0 to 17.2 mSv/y.     

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

ABSTRACT

Radon, 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.