Differences of natural radioactivity and radon emanation fraction among constituent minerals of rock or soil

We examined differences in the radioactive characteristics among the main minerals forming granite materials. Using a non-toxic high-density agent, minerals were separated from rock (granite–gneiss) and soil (weathered granite) samples. The natural radioactivity (²³⁸U and ²²⁶Ra) and radon emanation fraction of the minerals were then studied by gamma-ray spectrometry. The radon emanation fractions (27–43%) of the minerals from the soil were much higher than those (0.6–4.6%) of the rock minerals. Additionally, the emanation fractions differed greatly among the minerals separated from both the bulk rock and soil. These results were discussed in terms of the differences of surface area and radium distribution in the mineral grains. It was noticeable that a higher emanation fraction than expected for quartz was commonly observed in the rock and soil samples. We then estimated the contribution of each constituent mineral to the total radon exhalation from the bulk samples. The result depended not only on the radon emanation fraction, but also on the ²²⁶Ra activity and the mineral content. Furthermore, using the obtained data, we also discussed the effect of grain size on radon emanation and why this has been reported to vary markedly in previous studies.     

Estimating the radon emanation coefficient from crystalline rocks into groundwater.

A simple method is proposed to estimate the coefficient of radon emanation from crystalline rocks into underground waters. In these cases, the crystalline rock seems as both the source and the reservoir of the radon. The calculations are based on a formula proposed by Maché for determining the concentration of radon in underground waters. Due to the inaccuracy of estimating some parameters (e.g. porosity), the results have a significant error. The advantage of this method is its simplicity and the possibility of obtaining results in a relatively short time. The estimated values of the emanation coefficient for selected crystalline rocks of the Sudety Mountains (SW Poland) vary from 7 to 41%, and after considering the error resulting from the estimation of rock porosity, saturation and density, the values range from 5 to 60%. The highest values of emanation coefficient (41, 33 and 21%) have been obtained for rocks in areas of tectonic dislocations and the lowest ones are for rocks outside dislocation zones (9 and 7%). The calculations imply that the emanation coefficient of rocks may have a greater influence on radon concentration in underground waters than the contents of radium in the reservoir rocks.     

First model of the effect of grain size on radon emanation

The present model represents an improvement on previous models of radon emanation from soil by incorporating soil grain size in addition to moisture. Monte Carlo simulation was employed in the calculation since it was difficult to mathematically express the radon emanation fraction for the present soil model. Grain size is one of the most important factors in describing the properties of soil. Grain size was demonstrated to affect the radon emanation fraction, depending on moisture content. Although the emanation fraction is generally considered to be proportional to grain size, the result of the model calculation suggested that the effect of grain size is not so simple. This study should serve as an initial step toward improving the modeling of this radon emanation.     

Quantification of the dependency of radon emanation power on soil temperature

A study on the quantification of the dependency of the radon emanation power on soil temperature has been made using the accumulation method. The emanation from dry soil was studied at temperatures between −20°C and 45°C. A formula to calculate the radon emanation power as a function of the temperatures has been developed. The formula would contribute to the modeling of radon transport in soils and building materials.     

Measurement of radon and radon progenies at the German radon reference chamber.

The activity concentration of radon in the environment can vary over five orders of magnitude. Radon and its progenies thus concern all people involved in radiation protection as well as in low-level experiments. In the German radon reference chamber at the PTB, radon and its progenies are measured with different systems for alpha- and gamma-spectrometry with the full set of environmental parameters, e.g. temperature, humidity and aerosol concentration being controlled. Control of air pressure is also possible by use of an extention chamber. The sampling and measuring technique for radon and its short-lived progenies at the German radon reference chamber are the basis for fundamental studies with regard to the understanding of the equilibrium factor and the unattached fraction of progenies. The facility also serves for the calibration of radon progeny detectors.     

The radon emanation power of building materials, soils and rocks

The ²²²Rn emanation power of building materials, soil and rock samples is determined by collecting exhalated radon on activated charcoal. Median values are 0.2 for dry soils and stones, 0.06 for sand, 0.025 for bricks, 0.006 for ceramic tiles, 0.008 for mineral slag and 0.3 for gypsum. The emanation power of soil rises with water content, in accordance with literature. For water content above 10% the emanation power of soil is about twice as high as for dry soil.     

Measurement of radon emanation factor from granular samples: effects of additives in cement.

Two methods for radon emanation factor determination were performed and compared regarding their measuring accuracy: (a) by hermetically closing the sample in an airtight container and measuring the induced radon activity, and (b) by mixing charcoal and sealing the sample hermetically and after placing the sample in an open vessel with no charcoal addition, measuring each time the 226Ra content using gamma-spectrometry. Measurements of radon emanation factor of cement and pozzolanic additives, i.e. fly ash and phosphogypsum were also performed.     

A comparison between active and passive techniques for measurements of radon emanation factors

Some radon related parameters have been determined through two different techniques (passive and active) in soil and phosphogypsum samples. Emanation factors determined through these techniques show a good agreement for soil samples while for phosphogympsum samples appear large discrepancies. In this paper, these discrepancies are analyzed and explained if non-controlled radon leakages in the passive technique are taken into account.     

Measurement of radioactivity and radon exhalation rate in different kinds of marbles and granites

Geological materials usually contaminated with naturally occurring radioactive materials (NORM) have become a focus of great attention. These NORM under certain conditions can reach hazardous contamination levels. Some contamination levels may be sufficiently severe that precautions must be taken.

The present study deals with 60 geological samples (marble and granite) from both Egyptian and foreign locations. The studied samples were analyzed and the concentrations in Bq/kg dry weight of radioisotopes were determined by gamma-ray spectrometry using hyper-pure germanium (HPGe) detector in Bq/kg dry weight. The absorbed dose rate due to the natural radioactivity in the samples under investigation ranged from 2.45±0.07 to 64.44±1.93 nGy/h for marble and from 41.55±1.25 to 111.94±3.36 nGy/h for granite. The radium equivalent activity varied from 5.46±0.16 to 150.52±4.52 Bq/kg for marble samples and from 229.52±6.89 to 92.16±2.76 Bq/kg for granite. The representative external hazard index values for the corresponding samples are also estimated and given.

The radon exhalation rates for marble and granite samples were also calculated by using solid state nuclear track detector (CR-39). The value of radium exhalation rate varied from 8.0±2.39 to 30.20±5.06 Bq/m²/d for marble and 6.89±1.72 to 25.79±4.38 Bq/m²/d for granite and the effective radium content was found to vary from 1.700±0.51 to 6.42±1.08 Bq/kg for marble and 1.29±0.32 to 5.63±0.96 Bq/kg for granite. The values of the radon exhalation rate and effective radium content are found to correspond with the values of uranium concentration measured by the HPGe detector in the corresponding sample.     

Development of radon calibration chamber at KRISS.

Radon calibration chamber has been constructed to test and calibrate radon and radon progeny detectors at various environmental conditions and to study the characteristic behavior of radon decay products. The size of main room in the chamber is 3.2 m x 3.3 m x 2.4 m (25.3 m3) and the total volume of the chamber is 39.1 m3. The maximum concentration of radon in the chamber can be maintained up to 250 kBq m(-3) and temperature and humidity are controlled in the ranges of (10-40) degrees C and (30-80)%, respectively. The equilibrium factor and unattached fraction of radon progeny are determined at the radon concentration of 2 kBq m(-3).     

加气混凝土试块氡射气系数随含水率及环境条件变化的研究

目的 研究加气混凝土试块氡射气系数随含水率、温度和相对湿度的变化规律。方法 采用连续测氡仪和密闭累积腔体,测量加气混凝土试块在不同含水率(0~60%)、温度(10~40℃)和相对湿度(12%~95%)条件下的氡射气系数;并对测量结果进行回归分析,探讨氡射气系数(ε)与含水率(s)、温度(T)和相对湿度的变化规律。结果 加气混凝土试块的氡射气系数随着其含水率的增加呈对数型增长,ε=0.096·ln(s+2.43)+0.037,R²=0.952;加气混凝土试块的氡射气系数随着其温度的增加而增加,并呈线性增长关系,ε=0.002 45·T+0.060 1,R²=0.987;不同相对湿度下,加气混凝土试块的氡射气系数测量结果差异无统计学意义(P>0.05)。结论 含水率、温度变化对加气混凝土试块氡射气系数影响较大,在建材氡放射性危害评价与控制体系中应注意这些因素对加气混凝土试块氡射气系数的影响。     

Determination of 222Rn emanation fraction and diffusion coefficient in concrete using accumulation chambers and the influence of humidity and radium distribution.

In this paper we present a laboratory method for the determination of diffusion coefficient, D, as well as the 222Rn emanation fraction, f, in concrete core samples. It is based either on the analyses of the growth curves of the radon in the air volume surrounding a sample enclosed in an accumulation chamber (Lucas cell or RADIM device) or using the charcoal adsorption method. Samples used have a special geometry allowing the assumption of a one-dimensional diffusion of radon in material. Radium was enhanced in the concrete samples by adding radium bromide solution or uranium ore. A strong dependence of the emanation fraction on the enhancing method was observed. For the sample enhanced with uranium ore the specific exhalation rate was about ten times smaller. A marked dependence of radon exhalation on the water content was also observed.     

Unattached fraction and size distribution of aerosol-attached radon progeny in the open air

Unattached fractions of the radon progeny ²¹⁸Po and ²¹⁴Pb, size distributions for both unattached ²¹⁸Po and ²¹⁴Pb, and attached ²¹⁴Pb and ²¹⁴Bi, along with condensation nuclei (aerosol-particle concentrations), were measured in the open air of the city of El-Minia, Egypt. The measurements were performed with a wire-screen diffusion battery and a low-pressure Berner cascade impactor using standard methodologies. The results for parameters of derived distributions demonstrate that the distributions for the former (unattached ²¹⁸Po and ²¹⁴Pb) are nearly similar. The diffusion equivalent diameters (d_f) of ²¹⁸Po and ²¹⁴Pb were determined to be 1.4 and 1.55 nm with relative geometric standard deviations (σ_g) of 1.65 and 2.1, respectively. The latter distributions (attached ²¹⁴Pb and ²¹⁴Bi) are nearly identical. Most of the activities were associated with the aerosol particles of the accumulation mode. The mean activity median aerodynamic diameters (AMAD) of ²¹⁴Pb and ²¹⁴Bi have the same value of 380 nm but the relative geometric standard deviation of the log-normal distribution of ²¹⁴Pb shows a broader activity distribution than ²¹⁴Bi (σ_g = 2.2 for ²¹⁴Pb and σ_g = 2.05 for ²¹⁴Bi).     

Carcinogenicity of radon/radon decay product inhalation in rats--effect of dose, dose rate and unattached fraction

PURPOSE: The effects of inhalation of radon/radon decay products at different total doses, dose rates and 'unattached' fractions were investigated in a life span study in rats. MATERIALS AND METHODS: 1574 rats inhaled radon/radon decay products in a purpose-built recirculating exposure system that provided stable/reproducible exposure conditions. 501 were maintained as controls. RESULTS: Lung tumour incidences were significantly elevated in most exposed groups. The study power was insufficient to resolve the shape of the dose and dose rate response curves, but combination of this data with that from other studies demonstrated that for high cumulative exposures, the lifetime excess absolute risk increases with increasing exposure durations and for low cumulative exposures the opposite trend occurs. Exposure did not increase leukaemia incidences. A small number of non-lung tumour types including mammary fibroadenoma showed elevated incidences in some exposed groups, however not consistently across all exposure groups and showed no dose or dose rate relationship. CONCLUSIONS: Radon/radon decay product exposure caused excess lung tumours in rats along with limited non-lung effects. The results are consistent with the findings that at low cumulative exposures decreasing exposure concentrations or protracting the time over which the dose is delivered, reduces lung tumour risk. At higher levels, decreasing exposure concentrations or protracting exposure time increases lung tumour risk.     

Absorbed fraction of radon progeny in human bronchial airways with bifurcation geometry

PURPOSE: The absorbed fraction, defined as the portion of the initial particle energy which is absorbed in the tissue of interest, was calculated, under bifurcation geometry of the airway tubes, for alpha-particles emitted from radon progeny in the human respiratory tract. The results are given for all branching generations and compared with the data obtained for the commonly used infinite straight cylinders adopted by the International Commission on Radiological Protection (ICRP) Report 66. MATERIALS AND METHODS: A model was created to calculate the absorbed fraction of alpha-particle energy in the human lung using bifurcation geometry. Monte Carlo simulations of alpha-particle propagation in tissue and air were performed. The stopping powers of alpha-particles were adopted from the International Commission of Radiation Units and Measurements (ICRU) Report 49. RESULTS: The absorbed fractions for the bifurcation geometry are given for the 15 generations in the tracheobronchial tree for alpha-particle energies of 6 and 7.69 MeV. The sources were assumed to be the fast and slow moving mucus. CONCLUSIONS: Comparisons with ICRP66 data reveal that the assumption of long, straight cylinders was appropriate in some cases, but not in all. Adoption of the absorbed fractions obtained from the bifurcation model instead of the ICRP66 data caused 'redistribution' of doses in the bronchial (BB) and bronchiolar (bb) regions.     

Measurement of equilibrium factor and unattached fraction of radon progeny in Kaohsiung, Taiwan

To reasonably estimate the population dose from radon, equilibrium factor, Fp, and unattached fraction, fp, of radon progeny are important parameters. A Lucas cell and a working level monitor was used for most Fp measurement. The unattached fraction was measured by SARAD EQF3020. A detached house was chosen to measure the Fp in different rooms. The Fp value depended mainly on the ventilation rate and surface to volume ratio of the rooms. Fp and fp were measured in bedrooms of 14 other dwellings. Two hospitals were also chosen for measurement of Fp in the working place using rooms located in the basement. The average Fp for dwellings was about 0.5 and the average unattached fraction was about 0.055. The radon levels in the hospitals were higher than those in the dwellings but the equilibrium factors in the hospital were very low (about 0.06). The low Fp was attributed to the use of a dehumidifier in the hospitals. Dehumidifiers are popular for reducing fungi problem induced by the high humidity in Taiwan.     

Absorbed fraction of radon progeny in human bronchial airways with bifurcation geometry

Purpose : The absorbed fraction, defined as the portion of the initial particle energy which is absorbed in the tissue of interest, was calculated, under bifurcation geometry of the airway tubes, for alpha-particles emitted from radon progeny in the human respiratory tract. The results are given for all branching generations and compared with the data obtained for the commonly used infinite straight cylinders adopted by the International Commission on Radiological Protection (ICRP) Report 66. Materials and methods : A model was created to calculate the absorbed fraction of alpha-particle energy in the human lung using bifurcation geometry. Monte Carlo simulations of alpha-particle propagation in tissue and air were performed. The stopping powers of alpha-particles were adopted from the International Commission of Radiation Units and Measurements (ICRU) Report 49. Results : The absorbed fractions for the bifurcation geometry are given for the 15 generations in the tracheobronchial tree for alpha-particle energies of 6 and 7.69 MeV. The sources were assumed to be the fast and slow moving mucus. Conclusions : Comparisons with ICRP66 data reveal that the assumption of long, straight cylinders was appropriate in some cases, but not in all. Adoption of the absorbed fractions obtained from the bifurcation model instead of the ICRP66 data caused 'redistribution' of doses in the bronchial (BB) and bronchiolar (bb) regions.     

Calibration of commercial radon and thoron monitors at stable activtiy concentrations

The upcoming revision of Council Directive 96/29/Euratom in the form of the proposed basic safety standards for protection against the dangers arising from exposure to ionizing radiation (BSS) evokes new challenges for the metrology institutes. In the case of the two radon isotopes, the corresponding public exposure will be part of legal metrology for the first time. Since the levels of activity concentration that are laid down in the draft of the BSS cover the range from 200 Bq/m³ to 300 Bq/m³ in general (with an exceptional top level of 1000 Bq/m³), new calibration procedures for existing commercial monitors with their limited counting statistic have to be developed. This paper gives an overview how this metrological challenge can be overcome.     

Radioactivity of the Bega sediment-case study of a contaminated canal.

The Bega canal is one among many heavily polluted canals in Vojvodina (the northern province of Serbia and Montenegro). In the framework of the revitalization of this canal, the radionuclide content of the sediment was investigated in order to support the safe deposition after excavation. It was found that, in comparison with the Danube sediment and Vojvodina soil, the Bega sediment is contaminated with (238)U and (137)Cs. The origin of this contamination is discussed. No traces of contamination by nuclear power plants in the region were found, while the presence of technologically enhanced, natural occurring radioactive materials (TENORM) was proved.