Study of the influence of the lithological and hydrogeological parameters of aquifers on the radon emanation from underground waters using solid state nuclear track detectors

Radon-to-thoron ratios as well as radon and thoron activity concentrations in different underground water samples belonging to different aquifers in the Moroccan Middle Atlas area have been evaluated by LR-115 and CR-39 solid state nuclear track detectors (SSNTD) using a new calibration method. The radon isotope (²²²Rn) was used as a tracer for studying the water exchange between different aquifers of the area studied. The influence of the lithological and hydrogeological parameters of the aquifers on radon emanation were investigated.     

Concentrations of radon,thoron and their decay products measured in natural caves and ancient mines by using solid state nuclear track detectors and resulting radiation dose to the members of the public

Alpha- and beta-activities per unit volume of air due to radon (²²²Rn), thoron (²²⁰Rn) and their progenies were measured in the air of natural caves and ancient mines as well as inside different reference atmospheres by using CR-39 and LR-115 type II solid state nuclear track detectors (SSNTDs). In addition, the radon concentration was continuously measured inside one of the studied caves by using the SSNTDs’ method and AlphaGuard counter. Equilibrium factors between radon and its daughters and between thoron and its progeny were evaluated in the studied atmospheres. Alpha-activities due to ²¹⁸Po and ²¹⁴Po short-lived radon decay products were determined in different compartments of the respiratory tract of members of the public. The committed equivalent doses due to the ²¹⁸Po and ²¹⁴Po radon short-lived progeny were evaluated in different tissues of the respiratory tract of the visitors of the considered caves and ancient mines. Annual effective doses due to radon progeny from the inhalation of air by the visitors of the studied caves and ancient mines were evaluated.     

The Hydraulic Exchanges between the Main Water Reservoirs of the Moroccan Middle Atlas Region Measured by Solid State Nuclear Track Detectors

Uranium and thorium contents were evaluated in water samples collected from different sources of the piedmont of the Middle Atlas mountains by using two types of solid state nuclear track detectors (SSNTD). In addition, the radon (²²²Rn) and thoron (²²⁰Rn) -activities per unit volume of the water samples were also determined. The influence of the water flow rate and altitude on the radon concentration of the water samples belonging to the piedmont of the Middle Atlas mountains was investigated. The hydraulic exchanges between the Middle Atlas water reservoirs and the Turonian aquifer of the neighbouring Tadla plain have been quantified. The results were compared with data given in literature.     

The influence of the lithology and depth on water recharge of wells in two Moroccan Atlantic coastal regions by using solid state nuclear track detectors and radon as a natural tracer

Uranium and thorium contents as well as radon and thoron -activity concentrations were evaluated inside different underground water samples by using a method based on calculating the CR-39 and LR-115 type II solid state nuclear track detectors (SSNTDs) detection efficiencies for the emitted -particles and measuring the resulting track density rates. The validity of the SSNTD technique utilized was checked by analysing uranium nitrate standard solutions. A relationship between water radon concentration and recharge of wells dug in two Moroccan Atlantic coastal regions, for a given lithology, was found. The influence of the lithology and depth on radon concentration and salinity of well waters studied was investigated.     

Measurement of 222Rn and 220Rn decay product deposition velocities using SSNTD based passive detectors

In the present study, the deposition velocities of ²²²Rn/²²⁰Rn decay products were measured experimentally using SSNTD based passive detectors, direct radon progeny sensor (DRPS) and direct thoron progeny sensor (DTPS) and the results were compared with obtained values by Monte-Carlo simulations. In both cases, deposition velocities were found to be log-normally distributed and also the experimentally measured geometric mean (GM) and geometric standard deviation (GSD) of (0.12, 1.85) m h^?1 for radon decay products and (0.07, 1.75) m h^?1 for thoron decay products were found to be in good agreement with the simulated values.     

Determination of committed effective doses from annual intakes of 238U and 232Th from the ingestion of cereals, fruits and vegetables by using CR-39 and LR-115 II SSNTD

Uranium (²³⁸U) and thorium (²³²Th) concentrations were evaluated in different cereal, fruit and vegetable samples by using a method based on the calculation of the detection efficiencies of the emitted a-particles by CR-39 and LR-115 type II solid state nuclear track detectors (SSNTD) and measuring the resulting track densities. The influence of the soils on which the plants grow, and the fertilizers used was investigated. Total daily intakes of ²³⁸U and ²³²Th for a typical food basket were estimated to be 1.16 Bq^.d^-1 and 0.94 Bq^.d^-1, respectively, corresponding to a total committed effective dose of 0.27^.10^-7 Sv^.d^-1. Annual committed effective doses due to ²³⁸U and ²³²Th originated from the ingestion of different foodstuffs were evaluated for the adult members of the population by using the ICRP ingestion dose coefficients.     

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.     

Low Level Measurement of Plutonium Content in Bioassay Using SSNTD Alpha-Spectrometry

Solid state nuclear track detectors (SSNTD) find wide application in registration of different types of ionization irradiation due to excellent features: low cost, compactness, passivity and possibility of long term exposure for low activity measurements. One of the most shortcomings is in complex processing of the detector surface and following image analysis. However, present methods which allow reconstruction of track ranges and particle energies are intensively being developed. A developing trend in SSNTD alpha-spectrometry uses automated scanning microscope systems and specially designed mathematical software. Several parameters obtained from the analysis of etched tracks indi information about alpha-particle ranges in detector. The possibility to use some parameters (minor axis m and track end diameter d) for the spectrometry has been reported earlier. Intercomparison of SSNTD with semiconductor detectors (SCD) for ^238,239Pu content in bioassay within the interval 10^-3 to 1 Bq has been carried out. This comparison has demonstrated a good coincidence between these independent radiometric methods. A perspective of SSNTD use for spectrometric determination of low level activity is discussed. The background level playing a main role in low level detection has been also estimated. Influence of radon and thoron has been found as insignificant.     

Measurement of radon in air by α track method enhancement of detection sensitivity using a lamp

A new α track method is proposed for the measurement of radon (²²²Rn) concentration in environmental levels. This involves collecting radon daughters on the surface of pilot lamp and detecting α-particles emitted from the nuclides (²¹⁸Po and²¹⁴Po) by a detector (LR 115). The detection sensitivity of this method is 6 times greater than that of the conventional α track method.     

Influence of pollution and building materials on domestic radioactivity in Marrakechi dwellings

Domestic radioactivity has been studied by using LR-115 and CR-39 solid state nuclear track detectors (SNTD) and a suitable beta- and gamma-gaseous counter. A new calibration method, based on measuring thoron (²²⁰Rn) to radon (²²²Rn) ratios, has been developed for determining the -activity originating from radon in different Marrakechi dwellings. The influence of building materials as well as pollution and airing factors, on domestic radioactivity has been investigated.     

Determination of the radon diffusion coefficient and radon exhalation rate in Moroccan quaternary samples using the SSNTD technique

Measurements have been made of radon (²²²Rn), release from diverse quaternary samples collected from different sediment deposits in the Errachidia and Beni-Mellal areas (Morocco). The radon diffusion coefficient as one of some important parameters of radon transport in the soil has been measured using solid state nuclear track detectors (SSNTD). Radon -activity, uranium content and radon exhalation rate have been determined in the studied samples. Uranium concentrations were found to vary from 0.14 to 9.52 ppm whereas the radon exhalation rate varied from 0.003 to 0.145 Bq^.m^-2.h^-1. A positive correlation has been found between radon exhalation rate and uranium content in the studied samples. The average radon diffusion coefficients were found to vary from (1.26±0.09)^.10^-6 m^2.s^-1 to (4.3±0.36)^.10^-6 m^2.s^-1. Furthermore, the correlation between ²²²Rn diffusion coefficient and porosity are also discussed.     

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.     

Effects of negative ion generators on radon- and thoron-progeny concentrations in an occupied residence

Operation of negative ion generators in three rooms of an occupied residence caused decreases in indoor concentrations of the radon decay products²¹⁸Po,²¹⁴Pb and²¹⁴Bi, and of the thoron progeny²¹²Pb. Activity levels of²¹²Pb were lowered more than those of²¹⁴Pb, resulting in a decrease in the potential alpha energy concentration ratio, PAEC(Tn:Rn). The change in PAEC(Tn:Rn) is a function of the halflives of²¹⁴Pb and²¹²Pb and their respective precursors and is similar to the effect brought about by increased room ventilation. Decay products are also removed from indoor air by plateout of charged particles on room walls. Plateout rates calculated for²¹⁴Pb suggest that even in well-ventilated houses, the potential alpha energy concentration of radon is affected as much by wall plateout as by infiltration of outside air.     

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 flux variability with season and location in Tasmania, Australia

Radon (²²²Rn) and thoron (²²⁰Rn) fluxes were measured in locations in Tasmania and Victoria. Emphasis was on an evaluation of seasonal variability of the fluxes. The work is the first part of a program of mapping radon and thoron fluxes in the island of Tasmania on a scale commensurate with requirements of modelling the behaviour of environmentally important trace gases in a limited area around the Baseline Air Pollution Station at Cape Grim, Tasmania.     

Measurement of radon and thoron progeny size distributions and dose assessments at the mineral treatment industry in Thailand

A new portable type cascade impactor has been developed to determine the activity size distribution of radon and thoron progeny in a natural environment more efficiently. The modified impactor consists of 4 stages with a back up filter stage for the collection of aerosol samples. The aerosol cut points in the impactor are set for 10, 2.5, 1 and 0.5 μm at a flow rate of 4 L min^?1. Five CR-39 chips were used as alpha detectors for each stage. In order to separate α particles emitted from radon and thoron progeny, CR-39 detectors are covered with aluminum-vaporized Mylar films. The thickness of each film is adjusted to allow α particles emitted from radon and thoron progeny to reach the CR-39 detectors. The technique has been successfully tested in field studies, particularly inside a mineral treatment industry in Thailand to estimate doses in the working environment. The dose calculations by lung dose evaluation program showed that activity median aerodynamic diameters played a significant role in determining the particle size distributions of the attached radon and thoron progeny. The dose conversion factor determined from short term measurements due to exposure from the inhalation of thoron and its progeny was found to be 4 times higher than comparable values for radon and its progeny. The effective dose for workers exposed to radon is about 4–6 times higher than thoron.     

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.     

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.     

A new method for studying the influence of pollution and soil nature on the radon emanation from water samples by using solid state nuclear track detectors

Radon emanation from surface water and groundwater samples has been studied by using CR-39 and LR-115 solid state nuclear track detectors (SSNTD). A calibration method for determining the thoron and radon concentrations of the water samples studied has been developed. The effect of pollution due to coal fly ashes, cement and granite dusts on the radon emanation from water samples has been investigated. The influence of the radon source on the radon emanation rates from water samples has been studied.     

Background radiation study in Coimbatore city,Tamilnadu

The activity concentration and absorbed gamma dose rates due to primordial radionuclides (²³⁸U, ²³²Th and ⁴⁰K) have been determined for the soil of Coimbatore city using NaI(Tl) gamma-ray spectrometer. The average activity concentrations of ²³²Th, ²³⁸U and ⁴⁰K in the soil samples have been found to be 31.4 Bq·kg⁻¹, 12.8 Bq·kg⁻¹ and 698.0 Bq·kg⁻¹, respectively, which give the total gamma dose rate contribution of 56.4 nGy·h⁻¹. Grab sampling technique has been used to determine the indoor radon (²²²Rn) and thoron (²²⁰Rn) progeny levels in different dwellings in the city. The concentrations of radon and thoron progenies range from 0.4 to 10.4 and from 0.7 to 12.7 mWL with a mean value of 1.4 mWL and 3.1 mWL, respectively. The annual effective dose due to radon and thoron progeny has been found to be 0.14 mSv·y⁻¹.