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.     

An improved method for low-level222Rn determination in environmental waters by liquid scintillation counting with pulse shape analysis

A method in which²²²Rn is extracted from 0.5 1 water samples to 20 ml toluene is described. 10 ml toluene solution with extracted²²²Rn is directly added to a glass scintillation vial containing 10 ml of liquid naphthalene based scintillation cocktail. Apart from diluting by toluene, the final counting solution still has excellent properties in terms of: / separation by pulse shape analysis, detection efficiency and background in the -region. The detection limit of²²²Rn for 0.5 1 water samples was 1.5 mBq l^–1 (for 12,000 s count time). The concentration of²²²Rn in different environmental samples such as rain, tap and mineral waters as well as deep well waters were determined.     

Determination of neodymium isotopes as burnup indicator of highly irradiated (U,Pu)O2 lmfbr fuel

A new counting method was developed to determine²²⁶Ra in environmental samples by separating the equilibrated²²²Rn into a liquid scintillator. The integral counting method, which was originally developed for isolated individual radionuclides, was extended to the mixture of²²²Rn and its daughters in equilibrium. The optimum measurement conditions were established by examining the energy spectrum, counting time and quenching effect. An absolute counting was practiced by extrapolating the integral counting rate-bias voltage curve with the highest gain to zero bias. The detection limit thus obtained was 3 to 4·10⁻¹³ Ci.     

Spatial and temporal variations of radon concentrations in groundwater of hard rock aquifers in Madurai district,India

Radon (²²²Rn) and other radionuclides in groundwater can lead to health problems if present in higher concentrations. A study was carried out in Madurai district of Tamilnadu by collecting groundwater samples for four different seasons and aims to identify the regions with higher ²²²Rn concentration along with their spatial and seasonal variations. ²²²Rn has been compared with field parameters, log pCO₂, major ions and uranium to detect the factors responsible for the higher concentration in groundwater. The weathering process induces the release of higher uranium ions from the granitic terrain from the rock matrix which enhances the ²²²Rn levels in groundwater.     

Calibration and optimization of alpha-beta separation procedures for determination of radium/radon in single- and two-phase liquid scintillation systems

Liquid scintillation alpha beta discrimination technique based on pulse shape analysis (PSA) was evaluated for determination of ²²⁶Ra and ²²²Rn in water samples. In view of the significance of calibration, for the reliable and precise determination of ²²⁶Ra and ²²²Rn concentrations in water samples, calibration procedures were standardized for single and two phase systems using Quantulus 1220 liquid scintillation counter. PSA optimization and efficiency calibrations were performed using ²²⁶Ra standard rather than conventionally used pure alpha and beta standards and substantiated by measuring the activity concentrations of ²²⁶Ra and ²²²Rn in the spiked water samples.     

A simple method for the determination of natural uranium and226Ra in waters and soils

A procedure for the determination of natural uranium and²²⁶Ra in waters and soils has been carried out and applied to the analysis of samples for environmental radiological monitoring.²²⁶Ra determination consists of co-precipitation with BaSO₄,²²²Rn emanation in toluene and finally liquid scintillation counting. Natural uranium is then determined by a fluorometric technique. This paper describes the method and the conditions that were tested to optimize it. The technique was found to be suitable for the analysis of surface and ground waters, samples from rivers, streams and lakes and soil samples, because of its few steps, short processing time, high recovery percentages and suitable detection limits.     

Solvent extraction of uranium(VI) with benzyloctadecyldimethylammonium chloride (BODMAC) from highly concentrated chloride solution

The ²²²Rn emanation fraction (EF) released from the technically enhanced naturally occurring radioactive material (TE-NORM) wastes at certain sites of petroleum and gas production was determined. The samples were analyzed by γ-ray spectrometry to determine the activity concentration of the ²²⁶Ra content, of which the ²²²Rn emanation fraction was calculated. The results showed that the ²²²Rn emanation fraction differs in the oil and gas production sites and it is independent of the activity concentration of ²²⁶Ra. This revised version was published online in August 2006 with corrections to the Cover Date.     

Occurrence of the radionuclides in groundwater of crystalline hard rock regions of central Tamil Nadu,India

A study was conducted to understand the occurrence of the radionuclides in groundwater of crystalline hard rock region. Samples were collected to analyze major cations, anions, U, ²²²Rn and stable isotopes of oxygen, hydrogen. It was inferred that few samples have U and ²²²Rn concentrations higher than the permissible limit of drinking water standard. High degree of weathering of granitic rocks and long contact time of groundwater with the aquifer matrix could be the reason for enhanced U and ²²²Rn levels in groundwater. The association of U with SO₄ also proves that there exists anthropogenic influence in groundwater composition.     

Application of the relative uranium-series disequilibrium in soil to locate and/or confirm precisely active fault traces: A new technique

Fault traces have been previously located from measurements of ²²²Rn in soils taken a constant soil-depth across the fault trace. In this paper, we have studied the uranium-series disequilibria of the ²²⁶Ra, ²²²Rn (gas) and ²¹⁴Bi radionuclides, not only for their horizontal spatial patterns across the fault trace, but also for their vertical spatial patterns near and at the fault trace itself. Radon-222 activities in the soil-gas were measured on-site with a radiation monitor and a Lucas cell. Radium-226 and ²¹⁴Bi were determined in soil samples in the laboratory by gamma-ray spectroscopy. A new technique employing the measurement of ²²²Rn versus soil-depth shows a decrease in ²²²Rn activity at the fault trace due to the much higher soil-gas permeability as a result of the fractured soil, as well as relative larger uranium-series disequilibria, in respect to an increase in ²²²Rn activity at normal sites, where the soil is not fractured. Finally, it is suggested that fault trace detection could possibly also be performed by measuring ²¹⁴Bi in surface soils (0-100 cm) along a transect.     

Two new methods of determining radon diffusion in fish otoliths

Otoliths are bony structures found in the ears of fish and used in the²¹⁰Pb/²²⁶Ra dating method for age determination. This paper checks the assumption that²²²Rn is not lost from or added to orange roughy fish otoliths by diffusion, which would invalidate the technique. The first method of monitoring diffusion relies on measuring the gamma activity of daughter radionuclides. Otoliths were exposed to an atmosphere enriched in²²²Rn for 10 days, and the supported gamma activity inside them measured allowing for various decay corrections. The calculated radon addition was (0.5±0.5)% of the activity of the²²⁶Ra present. The second method used an alpha spectrometer and attempted to detect²²²Rn directly outgased from otoliths in the detector vacuum chamber. The results were consistent within errors with those of the first method and showed no loss or gain of²²²Rn, supporting previous estimates of a long life-span for the orange roughy. In contrast it was found that approximately 10% of²²²Rn formed in orange roughy fish scales was lost to an evacuated environment, (hence perhaps to an aqueous environment) and that for this species it could be difficult to base a dating method on analysis of scales. Nevertheless a preliminary minimum age of 57 years was obtained. The methods could be used with non-biological samples to determine²²²Rn diffusion rates.     

CFD-based simulation and experimental verification of 222Rn distribution in a walk-in type calibration chamber

A walk-in type ²²²Rn calibration chamber (~ 22 m³) is established at the Centre for Advanced Research in Environmental Radioactivity (CARER), Mangalore University, India which is being used by research groups working on ²²²Rn in India and other countries as well. In recent times, computational fluid dynamics (CFD) technique is opted as an alternative approach for the prediction of ²²²Rn concentration profile in the closed domain. CFD simulations were carried out to study the transient build-up and spatial behavior of ²²²Rn concentration in the calibration chamber. Measurements were performed using active ²²²Rn measuring devices and results of the CFD predictions and direct measurements were compared. A good agreement was observed between the simulated and experimental results with deviation between the two entities being ~ 3% in the case of transient build up and ~ 8% in the case of spatial distribution of ²²²Rn concentration.

     

Natural radioactivity of geothermal water in Beijing,China

In this work, we collected 101 geothermal water samples to investigate comprehensively the radioactivity of geothermal water in Beijing. The concentrations of gross beta, ²²⁶Ra and ²²²Rn were measured and the obtained values were in the range of 0.032–7.060, 0.023–0.363 and 0.470–29.700 Bq/L, respectively. The samples with higher concentration of ²²²Rn were found to be located near large faults. The effective dose of ²²²Rn in the air for three cases were calculated to be greater than radiation dose limit of 1 mSv/a.     

Radon concentration in dwellings in Aomori Prefecture, Japan

To obtain an average dose from ²²²Rn to the people in Aomori Prefecture where the first Japan"s nuclear fuel cycling facilities are now under construction, we surveyed ²²²Rn concentrations in 109 dwellings in the Prefecture from 1992 to 1996. The outdoor ²²²Rn concentrations were also measured in gardens of 15 dwellings. The ²²²Rn concentrations were measured with passive ²²²Rn detectors which used a polycarbonate film for counting a-ray and could separate concentrations of ²²²Rn from ²²⁰Rn. Counting efficiencies of the detectors were calibrated with a standard ²²²Rn chamber in the Environmental Measurement Laboratory in USA and in the National Radiological Protection Board in UK. Geometric means of ²²²Rn concentration were 13 and 4.4 Bq^.m^-3 in the dwellings and outdoor, respectively. These values were consistent to nationwide survey results in Japan. The ²²²Rn concentrations in the dwellings depended on their age. The concentrations were higher in recent dwellings than in older ones. The radiation dose from ²²²Rn was estimated, taking into account the occupancy factor for inside and outside of dwellings. The annual dose was 0.32 mSv^.y^-1, and 99% of the dose came from the exposure to ²²²Rn inside the dwelling.     

222Rn determination in drinkable waters of a central eastern Italian area: Comparison between liquid scintillation and gamma-spectrometry

Summary It is well known that the interest in radon concentration indoor as a pollutant emerged during the energy crisis of seventies which led to reduce ventilation in dwellings. Recently the Euratom Recommendation 2001/928 suggested the necessity of performing frequent ²²²Rn checks on tap waters. As a consequence of this Recommendation, Urbino and Perugia Universities carried out a preliminary ²²²Rn determination on tap waters of the Pesaro-Urbino province. Samplings were carried out in twenty-eight sites and radon concentration was determined by liquid scintillation counting and gamma-spectrometry. The results obtained by the two techniques were comparable (the deviation from the mean is lower than 10% for 54.5% of the samples). The resulted ²²²Rn concentration was very low (5 Bq ^. l^-1 for 43% of the samples) and, therefore, radon in waters cannot be considered as a direct radiological risk for the local population.     

Radon isotope assessment of submarine groundwater discharge (SGD) in Coleroon River Estuary,Tamil Nadu,India

Submarine groundwater discharge is the fresh groundwater discharge to sea that impacts the coastal regions. Radon (²²²Rn) isotope has been used to quantify SGD in coleroon river estuary, India. Continuous ²²²Rn analyses were attempted for 10 days in groundwater and pore water samples at three different locations. ²²²Rn in groundwater ranges between 35.0 and 222.0 Bq m^?3 and in pore water between 14.0 and 150.0 Bq m^?3 irrespective of locations. The radon mass balance estimated total SGD rate ranges between 2.37 and 7.47 m days^?1. The SGD increases with distance from coast, influenced by tides and hydrological features.     

Assessment of <Superscript>222</Superscript>Rn concentration and terrestrial gamma-radiation dose rates in the seismically active area

²²²Rn concentrations along the seismic active area (some distinct in East Anatolian Active Fault System (EAFS), Turkey) were determined by using passive and active (prompt) methods including CR-39 and Markus-10, respectively. It was observed that the changing of ²²²Rn concentration along the fault lines, crossing the main East Anatolian Fault Line, has shown similar characteristics for both methods. The mean ²²²Rn concentrations were found to be between 1.2 and 3.6 kBq·m⁻³ and, 2 and 70 kBq·m⁻³ by using passive and prompt methods, respectively. Nevertheless, some measured terrestrial gamma-radiation dose rate in the same area has weak positive correlation to ²²²Rn concentration. Terrestrial gamma-dose rate at 1 m above the ground in the same sampling point, as for ²²²Rn concentration measurement were made, varied from 8.5 to 10.6 μR·h⁻¹.     

New rapid method to determine radon and thoron from a single counting sequence using a field portable alpha particle scintillometer

Measurement of soil-gas radon (Rn) concentration is an important parameter in estimating soil Rn potential for a building site. Typically, field methods for grab samples (as contrasted with continuous flow systems) using a protable alpha-scintillometer only considered²²²Rn (T _1/2= 3.8 d) and ignored²²⁰Rn (T _1/2=55 s). Now the calculation permits the determination of the concentrations of both isotopes with a single series of readings. A sample is collected and within 1 minute is introduced into the counting system. A series of 1 minute counts begins immediately and continues for 10 minutes. If high²²⁰Rn concentrations are present, there will be a rapid decay followed by a steady ingrowth of²²²Rn progeny. If very little²²⁰Rn is present, the ingrowth will be seen immediately. In either case, a non-linear least square fitting program from Statgraphics is used to obtain both concentrations at time zero. When inexact timings ranging from 1 to 30 seconds were imposed on the measured data, the method proved to be very robust; the biases did not exceed 15 percent.     

Direct determination of 226Ra in NORM/TENORM matrices by gamma-spectrometry

Summary The main shortcoming with the procedure to determine ²²⁶Ra in a gamma spectrum of an environmental sample by means of the ²¹⁴Bi and ²¹⁴Pb photopeaks is the likelihood of ²²²Rn leakage from the sample counting vial. An option to make such determination is to disregard the ²²⁶Ra gamma-contributions to the spectrum, other than 186.2 keV (3.5%), subtracting the ²³⁵U contribution to the ²²⁶Ra+²³⁵U peak at 186 keV. The use of this option to determine directly ²²⁶Ra activity concentrations in environmental samples and in NORM/TENORM matrices will be presented and discussed.     

Determination of thoron and radon ratio by liquid scintillation spectrometry

Summary A portable liquid scintillation counter was applied for the analysis of alpha-ray energy spectrum to determine the ratio of ²²⁰Rn/²²²Rn in fumarolic gas in the field. A surface-polished vial was developed, by which a Gaussian distribution could be approximated for the alpha-ray energy spectra and the peak areas of the nuclides could be estimated independently, because of the wide FWHM in the liquid scientillation pulse. A fumarolic gas sample was collected in Mt. Kamiyama (Hakoneyama geothermal field in Japan) having low ²²⁰Rn/²²²Rn ratio of 2.20±0.13.     

Simultaneous determination method of radon-222 and radon-220 by a toluene extraction-liquid scintillation counter

A new determination method for²²²Rn and²²⁰Rn in water sample was developed by extracting radon with toluene and applying the integral counting method with a liquid scintillation counter. The essential characteristics of the methods are, (1) extraction of radon with toluene from water, (2) finding absolute counts and making corrections for the quenching effect by the adoption of the integral counting method, (3) the determination of²²²Rn and²²⁰Rn was performed by counting the activity of²²⁰Rn with its descendants and of ThB (²¹²Pb) with its descendants in a radioactive equilibrium, respectively, (4) realizing high sensitivity by simultaneous counting of α, β⁻ particles emitted from the decay products formed in toluene. The lowest detection limit obtained by the present method was 5.0·10⁻¹³ Ci/l for²²²Rn and 6.8·10⁻⁸ Ci/l for²²⁰Rn in water.