Seasonal and diurnal variations of radon/thoron exhalation rate in Kanto-loam area in Japan

Radon and thoron concentration in the outdoor environment are affected by the magnitude of the exhalation rate that can vary diurnally and seasonally. This paper presents measurement results of radon and thoron exhalation rates and gamma-ray dose rate in different season at same location points in Gunma Prefecture Japan. Exhalation rates were measured by the MSZ instrument which is based on the accumulation method. Three measurement points Katashina Village, Midori City and Takasaki City were selected for measurement. Soil water saturation and soil temperature were measured to investigate their relationship with exhalation rate. The diurnal variation of exhalation rate may be correlated with soil temperature but no clear relationship was found between them. The gamma-ray dose rate do not vary significantly at the same places even in different season. The average radon exhalation rates were 11 ± 2, 2 ± 1, 5 ± 3 and 11 ± 4 mBq m⁻² s⁻¹ for spring, summer, autumn and winter, respectively. Those for thoron were 1,100 ± 100, 120 ± 30, 250 ± 80 and 860 ± 140 mBq m⁻² s⁻¹. Thus there was a variation of radon and thoron exhalation rate with different seasons. The radon and thoron exhalation rates in the summer and autumn surveys are higher than those in the spring and winter surveys which were affected by rainfall. It indicates that water saturation is an influential factor for radon and thoron exhalation rates.     

Radioactivity contents in building materials used in Hong Kong

The radioactivity contents in building materials used in Hong Kong were measured to determine the sources of the high indoor radon concentrations observed in local buildings. The radium contents and the radon emanation coefficients of different building materials were measured by high resolution γ-ray spectroscopy using germanium detectors. The radon exhalation rates were measured using scintillation cells by circulating the exhaled radon from building materials and obtaining the initial growth rates. The radium content and the radon exhalation rates of concrete and bricks used in Hong Kong were found to be higher than those in some other countries, resulting in high indoor radon concentrations probably due to the high radioactivity contents in the aggregates, granitic in nature, used in building materials.     

Natural radioactivity of building materials

Experiments were designed to measure trace uranium concentration and the rate of radon exhalation from masonry structural materials, both bare and surface finished and coated. LR115 cellulose nitrate track detectors were used to record the alpha emission from structural material surface. Fission track, neutron activation and fluorometric analysis methods were used to determine the uranium content. Most types of paints studied will reduce alpha contribution and radon emanation from building materials.     

Radon emanation coefficient and its exhalation rate of wasted petroleum samples associated with petroleum industry in Egypt

Wasted petroleum, scale and sludge, samples associated with petroleum industries have elevated level of radionuclides concentrations which increase the radiation dose received to the workers. Radon concentration, emanation coefficient and exhalation rate give good information about the radioactivity levels. Twelve samples of scale, sludge and sand, collected from different oil fields in the Red Sea Refineries company for petroleum services in the eastern desert of Egypt, were selected for this study. Radon concentration released from selected samples was measured using AlphaGUARD radon monitor. Radon emanation coefficient and its exhalation rate were calculated based on the measured value of radon concentration. Correlation among radon exhalation rate with radium content and “emanated radon concentration” (radium concentration × emanation coefficient) as well were found to be of 0.94 and 0.99, respectively. Therefore, radon exhalation rate could be useful index for both radium concentration and emanated radon. Radon emanation coefficient was increased more than twice due to water content within material of less than of 10 %.     

Radiological characterization of commercially available “radon spa sources”

Nowadays, artificial “radon spa sources” for home baths are commercially available. Although these sources could give a potential radiation exposure to the users, few studies have been reported on their radiological measurements. In the present study, five types of radon spa sources were collected and their radiological characterization was investigated. The followings were estimated for these samples: (1) radon emanation coefficients (dry and water-saturated conditions), (2) surface γ-ray dose rate, (3) surface count rates for α- and β-rays, (4) activity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K, and (5) concentrations of radon and thoron generated from the sources located in an air flow system. The activity concentrations were very high (except for one sample (named “sample B”), although radon emanation coefficient was low compared with soil. This leads to high concentrations of radon/thoron generated from the sample. The maximum surface γ-ray dose rate was observed for sample A (2.7 μGy h⁻¹). If people stay very close to the sample for a long time, the exposure might be significant.     

A new method for determining the radon emanation coefficients and radon production rates in different building materials using solid state nuclear track detectors

Radon α-activity concentrations have been measured inside and outside various building materials by combining a calculational method with the solid state nuclear track detector (SSNTD) technique. Radon emanation coefficients of the studied materials have been evaluated. A new calibration method for determining the radium (²²⁶Ra) and thorium (²³²Th) specific activities of the considered building materials has been developed. The radon production rates per unit volume of the studied materials have been evaluated. The influence of the material porosity on the radon emanation coefficient and radon production rate have been investigated.     

Concentration of radionuclides in building and ceramic materials of Bangladesh and evaluation of radiation hazard

The concentration of radioactive²²⁶Ra,²³²Th and⁴⁰K in building and ceramic materials of Bangladesh was investigated by γ-spectrometry with two HPGe detectors. Radium equivalent activities, representative level index values, criterion formula, emanation coefficients and²²²Rn mass exhalation rates were estimated for the radiation hazard of the natural radioactivity in the materials. The activity concentrations of the natural radionuclides, radium equivalent activities, emanation coefficients and²²²Rn mass exhalation rates are compared with the corresponding values for building and ceramic materials of different countries. The radium equivalent activities in the samples varied between 30.9 (mosaic stone) and 328.0 Bq·kg⁻¹ (gypsum). The emanation coefficient of the materials ranged from 7.83 (cement) to 33.0% (soil) and the²²²Rn mass exhalation rate ranged from 2.31 (stone chips) to 118.0 μBq·kg⁻¹·s⁻¹ (gypsum).     

Comparison of thoron (220Rn) content and gamma radiation level in high background radiation area of Kollam district in Kerala,India

In order to map the thoron prone areas of the coastal region of Kollam district, a well known HBRA of south India, comparative study of radon and thoron exhalation rate was conducted. The in situ measurement of radon and thoron exhalation has been taken. These studies were correlated with the gamma radiation level. The average value of thoron exhalation is found to 5.55 ± 1.35 Bq m⁻² s⁻¹ along the coastal areas and the radon exhalation rate is found to 107.6 ± 32 Bq m⁻² h⁻¹. The value of thoron exhalation was found 12 times greater than the global values in Neendakara and Chavara region and about 6 times greater in the Alappad region.

     

Measurement of the radon exhalation rate from the medium surface by tracing the radon concentration

The paper will present a method based on the accumulation chamber technique for measuring of radon exhalation from the medium surface. A radon monitor traces the change of radon concentration in the accumulation chamber, and then the radon exhalation can be obtained accurately through linear fit. Based on our recent experiments, the radon exhalation rate from the medium surface obtained from this method is in good agreement with the actual exhalation rate of our simulation facility. This method is superior to the competition method which obtains the radon exhalation through the exponential fit by an external PC-system. The calculation for the exponential fit is very easy by computer and related software. However, for portable instruments, the single chip microcomputer can’t calculate the exponential fit rapidly. Thus, this method is usable for developing the new portable instrument to classify building materials, etc.     

Assessment of the natural radioactivity using two techniques for the measurement of radionuclide concentration in building materials used in Japan

The specific activities of ²³⁸U, ²³²Th, and ⁴⁰K in selected building materials used in Japan were measured using a high-purity germanium detector. The uranium and thorium concentrations were determined from same samples using inductively coupled plasma mass spectrometry. There was a good agreement between the measurement of uranium and thorium with both methods (R ² = 0.94, and 0.97, respectively). Based on the specific activities, we have estimated some hazard indexes such as radium equivalent activities (Ra _eq), external hazard index (H _ex), internal hazard index (H _in), annual gonadal equivalent dose (AGED), internal alpha dose, mass exhalation rate and emanation coefficient of radon.     

Variation rules of the radon emanation coefficient in dump-leached uranium tailing sand

This study was intended to determine the variation rules of the radon emanation coefficient in dump-leached uranium tailing sand. A temperature and humidity controllable device for measuring the emanation coefficient was designed. Tailing sand with different grain sizes was selected from uranium tailings in southern China. An orthogonal experimental design was conducted to determine the radon emanation coefficient of the sand under different temperatures, humidities and grain sizes. Experimental results showed that the air temperature, humidity and grain size have significant effects on the emanation coefficient. The variation rules regarding the radon emanation coefficient showed significant reference value.

     

Radon health hazards of some rocks of Iranian origin, frequently used as building stones

Radon exhalation rate from various types of stones, used inside the living buildings, is a major factor for evaluation of the environmental radon level. To verify the significance and lethal impacts of this unknown and obscure source of radiation upon the people around the world, the exhaled radon gas concentrations from the rocks, granodiorite, granite, limestone and aragonite, and the effect of their block sizes on the exhalation rate, have been studied. The block samples, collected from their ores, were transferred to plastic containers in which the CR-39 detectors could properly be placed and air tightened, for concentration measurements. The results show the radon concentration of 7.4 ± 0.8, 6.6 ± 0.6, 0.08 ± 0.02 and 0.09 ± 0.02 kBq m⁻³ for granodiorite, granite, limestone and aragonite, respectively. The corresponding annual dose values in a closed environment are: 186 ± 20, 166 ± 15, 2.5 ± 1 and 2 ± 1 mSv y⁻¹. These absorbed dose values indicate that granodiorite and granite when used inside the buildings could increase the risk of various cancers while aragonite and limestone have much lower risks and are recommended for use inside the buildings. The former ones when used in the closure areas remedial action should be implemented. The results do not show obvious dependence between the rock size of the samples and their radon exhalation rate.     

Spatial and vertical distribution of radon and thoron in a typical Indian dwelling

Radon and thoron have been identified as potential radiological health hazard and the dose estimation due to their exposure is an important task. Understanding their behavior in indoor environment helps in calculating the inhalation doses due to them. Present study aims at the distribution of radon and thoron concentrations in a typical Indian dwelling. Solid state nuclear track detectors are employed in the study. The concentration of radon is found to be invariant in indoor environment. The thoron concentration is found to decrease exponentially as a function of distance from the source (wall/floor). Solution of one dimensional diffusion equation is used for regression fittings for thoron variation, from which the diffusion constants and the exhalation rates were calculated. The diffusion constants varied from 0.00195 to 0.00540 m² s⁻¹.     

Experimental study of radon and thoron diffusion through barriers

The radon chamber and radon calibration set have been modified for investigation of the diffusion coefficients of the barriers for reduction of radon exposure in the dwellings and for application as filters to separate radon and thoron. The volume radon activities have been measured by continuous monitors with scintillation cell or ionisation chamber. The theory on which the experimental determination of a barrier diffusion coefficient is based, is presented. The diffusion ability of radon has been studied for different materials and the results of the measurements are presented and discussed.     

Determination of the radon emanation fraction from phosphogypsum using LSC

A simple method for the determination of the radon emanation fraction was studied using a liquid scintillation counter. The radon activity of the gaseous phase in a closed container was measured 1 day and 35 days after sealing and used to calculate the radon emanation fraction. Radon leakage from the container was investigated using a ²²⁶Ra radioactive standard solution (SRM4967, NIST) to plot a radon growth curve. The method was applied to materials that typically contain a high level of radium, such as phosphogypsum, phosphate fertilizer and a rock sample. The effect of temperature on the radon emanation fraction from the materials was investigated at 0, 10, 20, 30 and 40 °C. It was found that there is a linear correlation (R ² = 0.746 − 0.946) between temperature and the emanation fraction. Within the temperature range, the radon emanation fractions were 0.241–0.466 for phosphogypsum, 0.225–0.351 for phosphate fertilizer and 0.154–0.351 for the rock sample.     

Thoron interference in radon exhalation rate measured by solid state nuclear track detector based can technique

This paper presents the extent of thoron (²²⁰Rn) interference in the radon (²²²Rn) exhalation rate, measured by solid state nuclear track detector based ‘Can’ technique. Experiments were carried out following the standard procedure of ‘Can’ technique as well as active technique as a reference method for ²²²Rn and ²²⁰Rn exhalation measurements. It was found that ²²⁰Rn interference may lead to overestimation of ²²²Rn exhalation by a significant factor which can be as high as 12 depending upon the rate of ²²⁰Rn exhalation from samples.     

The influence of the lithology and granulation on radon emanation in a sedimentary phosphatic deposit using solid state nuclear track detectors

Samples have been collected from different layers in a sedimentary phosphatic deposit and sieved. Different granulometric fractions have been selected. The uranium and thorium contents have been determined in each phosphate sample and its corresponding selected fractions. Radon (²²²Rn) α-activities per unit volume have been evaluated inside and outside each phosphate sample and its corresponding selected fractions by using CR-39 and LR-115 type II solid state nuclear track detectors (SSNTD). The radon emanation coefficient in each phosphate layer has been determined and the global radon alpha activity outside a parallelepipedic block of the layers studied was evaluated. The influence of the lithology and granulation on the radon emanation has been studied.     

Measurement of radon exhalation rate from soil samples of Garhwal Himalaya, India

Laboratory experiment was performed for the measurement of radon exhalation rate from the soil samples collected from Garhwal Himalayas. This study is accompanied by the measurement of soil-gas radon concentration in the same area. Both results were compared with the geological formation and structure of the area. No correlation was observed between soil-gas radon concentration and radon exhalation rate. However, it was found to be controlled by the lithology, geological structure and uranium mineralization in the area. The relationship between radon emanation, geological formation and occurrence of high indoor radon concentration is discussed.     

Study of the influence of porosity on the radon emanation coefficient in different building material samples by combining the SSNTD technique with Monte Carlo simulations

Radon alpha-activities per unit volume have been measured inside and outside different building material samples by using CR-39 and LR-115 type II solid state nuclear track detectors (SSNTD). Radon emanation coefficients of the studied building materials have been evaluated. The porosities of the building material samples studied have been determined by using a Monte Carlo calculational method adapted to the experimental conditions and compared with data obtained by the Archimedes's method. The influence of the building material porosity on the radon emanation coefficient has been investigated.     

Study of radon exhalation from the soil

The influence of meteorological parameters on radon exhalation rate was analyzed. The analyses show a significant influence of precipitation on radon exhalation rate. The highest exhalation rate was found during dry periods and the lowest during the periods of strong precipitation. We also tested two different types of detectors for the measurement of radon exhalation rate—the ionization chamber (AlphaGUARD) and the scintillation chamber of Lucas type. The exhalation rates measured by these detectors were in a good agreement. Likewise, there was an agreement in radon exhalation rates determined from short term and long term increases in radon activity concentration.