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.     

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.     

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.     

Seasonal variation of indoor radon/thoron and their progeny levels in lesser-Himalayas of Jammu & Kashmir,India

In this investigation, the passive estimation of radon (Rn²²²), thoron (Rn²²⁰) and their progenies have been measured in the dwellings of Reasi district of Jammu & Kashmir for a period of 1 year. These estimations have been done with the help of latest developed single entry Pin-hole based dosimeters and progeny sensors based on deposition. The annual Equilibrium factors for ²²²Rn, ²²⁰Rn, and their progenies have been calculated separately for each dwellings The average annual effective dose was found to be 0.9 ± 0.2 mSv/y for ²²²Rn, which is less than prescribed limit of ICRP. The results obtained indicate no vital health hazards because of exposure of Rn²²², Rn²²⁰ and their progenies.

     

Simple and rapid methods for on-site determination of radon and thoron in soil-gases for seismic studies

The determination of soil-gas anomalies especially ²²²Rn anomalies, are important to precisely locate fault traces, as well as to investigate earthquake precursors. In this paper, we have studied and compared new rapid methods for on site determinations of radon (²²²Rn), thoron (²²⁰Rn) and total radon (²²²Rn+²²⁰Rn) in soil-gas. These new techniques pump the soil-gas continuously from the soil through a simple sampling tube to the counting cell for one-minute with discarding the excess. Then, either four one-minute counting periods (5-minute technique) or nine one-minute counting intervals (10-minute technique) are followed immediately. In all the methods, conversely to Morse"s method, the first counting period (C1) was not employed for calculations. Three calculation methods for the five-minute technique, two for the ten-minute technique and a modified Morse"s method are compared with theoretical values and different real soil-gases with different radon/thoron ratios. The affect of different flow rates of soil-gases into the counting cell was also investigated. Finally, the ten-minute technique seems to be a little more accurate, but the 5-minute technique is much more suitable for seismic field studies when a much larger number of determinations are required in a short time.     

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.     

Determination of the distribution coefficients for134Cs,60Co and234Th in the Pinheiros River sediment-water

We have investigated the possibility of determining the relative concentrations of two radon isotopes (²²²Rn and²²⁰Rn) in the air, using solid state nuclear track detectors (CR-39) as alpha spectrometers. The detectors were exposed to²²²Rn and its daughters and²²⁰Rn and its daughters in the air. Analyzing only roundish tracks, it was observed that the performance of CR-39 as alpha spectrometer varies with etching time, improving markedly for long etching times.     

Detection of geological faults using a nuclear method

It proved possible to detect the precise location of large geological faults using the amount of⁴⁰K and²²⁰Rn daughter gamma-rays and the amount of²²²Rn (measured in a scintillation chamber) which could be extracted from the soil using negative pressure. Both⁴⁰K and²²⁸Th appear to be concentrated in fault gouge. The²²²Rn content extractable from the soil is a measure of permeability and is very low in the region of the fault due to clay-like fault gouge. The method was demonstrated successfully on the large Wellington fault at Upper Hutt, New Zealand.     

Assessment of Summer Trends of Tropospheric Radon Isotopes in a Coastal Antarctic Station (Terra Nova Bay)

This work reports the first results of atmospheric radon measurements performed at the Italian Antarctic station located at Terra Nova Bay (74.69°S; 164.12°E) during summer campaigns of 1995-96, 1996-97 and 1997-98. Mean²²²Rn concentrations was 0.51 - 0.43 Bq m^m3 (median = 0.37 Bq m^m3), and ranged from 0.01 to 2.74 Bq m^m3 . On the average, these values were considered high, in comparison to results reported for other sites in Antarctica at equivalent latitudes. This could be explained by two causes: radon data for Terra Nova Bay were only for the summer period, when the ice-free area is at its maximum and thus the radon emission to the atmosphere; and by the larger ice-free area at Terra Nova Bay compared, for example, to measurements taken at another Antarctic site by the same technique (Ferraz station - 62°05'S; 058°23.5'W). The mean ²²²Rn to ²²⁰Rn activity ratio was 4.4 - 4.2, ranging between 0.1 and 45.3. The highest ratios indicated that some of observed surges of concentration of ²²²Rn could be attributed to not local sources. Lower radon concentrations were observed during katabatic wind events. The diurnal radon variation followed the general trend observed for continental areas located at lower latitudes.     

Development of a sparging chamber for field radon analysis

Radon-222 has become a widely used tracer of submarine groundwater discharge. However, remote field studies are often limited by the need to pump water to a spray chamber which degasses dissolved radon for subsequent analysis in the gaseous phase. We develop here a new method of degassing dissolved ²²²Rn, utilizing a stream of bubbles driven by the internal air pump of a commercial radon analyzer to achieve air:water partitioning equilibrium, eliminating the need to pump water. This system utilizes a sparging chamber, comprised of a slotted vertically-oriented pipe with bubbles produced in the bottom. A non-slotted section of the pipe at the top of the chamber forms a sealed headspace, allowing air to be circulated in a closed loop between the sparging chamber and a radon-in-air monitor. We found that such a sparging chamber needs to allow bubbles to rise through at least 45 cm of water column to function at equal efficiency as the standard protocol of the spray chamber. Under our optimized configuration, the sparging chamber operates as efficiently as the standard protocol at measuring dissolved ²²²Rn activities when encountering increasing ²²²Rn activities, and offers even greater gas exchange efficiency when dissolved ²²²Rn activities decrease. The sparging chamber offers a more field-friendly alternative to measuring ²²²Rn activities, as it eliminates the need to maintain a submersible pump throughout the measurement and it offers increased temporal resolution when variable ²²²Rn activities are expected.     

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.     

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.     

A new method for determination of222Rn and220Rn in geothermal steam

The radionuclides²²²Rn and²²⁰Rn are measured by incorporating their daughters²¹⁴Pb and²¹²Pb in a very thin layer of PbS and accumulating the alpha spectrum of their daughter products²¹⁴Po and²¹²Po. The median yield was measured as 88% using a known amount of²¹⁰Pb tracer. A single fumarole and all 23 geothermal wells tested were found to contain²²⁰Rn. As isotopes of Th, Bi, Po and Ra, are also absorbed in the PbS layer, the method can be used for determinations of these in tap-water.     

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.     

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.     

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.     

Soil gases (222Rn, 220Rn and total radon) and 214Bi measurements across El Avila fault near Caracas, Venezuela

Summary Radon measurements were performed across two sections of the Avila fault near Caracas, Venezuela. The radon concentrations clearly showed the different tectonic features and lithology at the Tacamahaca and Spanish Trail sites. ²¹⁴Bi (U-cps) measurements also were related to the lithology. The passive radon method employed laboratory-made dosimeters with LR 115, type 2 celulose nitrate films as detectors. They were buried in the ground at 30 cm depth. While, the active radon method was performed with a Pylon radon measurement system with Lucas cells. The soil gas was also sampled at 30 cm depths, but for only one minute, which was sufficient to fill the 150 cm³ Lucas cells completely. The total radon counts were then separated into those corresponding to ²²²Rn (radon) and ²²⁰Rn (thoron) by a simple computer routine. A comparison of the active and passive methods for the Tacamahaca section over a three-month period showed that both methods could locate precisely the active fault trace.     

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.     

Synthesis and characterisation of scintillating microspheres made of polystyrene/polycarbonate for <Superscript>222</Superscript>Rn measurements

Several studies have demonstrated that polycarbonate-based polymers have good capacities for the absorption of ²²²Rn. Meanwhile, polystyrene polymers are reported to be the most appropriate for developing plastic scintillator materials for the detection of radioactivity. The objective of this work was to develop plastic scintillators in the form of microspheres (PSm) composed of polystyrene and polycarbonate that could be used to measure ²²²Rn and improve this performance thanks to the combination of characteristics of both polymers. Our results show that PSm of polystyrene and polycarbonate can be made via the evaporation/extraction method, despite the two polymers not being miscible. From the point of view of the radioactive measurements, we observed that the addition of polycarbonate causes quenching, although it does not significantly affect the detection efficiency for alpha and high-energy beta emitters. From the point of view of ²²²Rn absorption, we observed that synthesis of the PSm through the evaporation/extraction method changes the ²²²Rn absorption of the raw material. This result demonstrates that the method of production of the polymer and the resulting physical characteristics are a key parameter for its final ²²²Rn absorption properties.