Influence of the building material and ventilation rate on the concentration of radon, thoron and their progenies in dwelling rooms using SSNTD and Monte Carlo simulation

A new Monte Carlo computer code was developed for determining the detection efficiencies of the CR-39 and LR-115 II solid state nuclear track detectors (SSNTD) for a-particles emitted by radon (²²²Rn) and thoron (²²⁰Rn) series inside the atmosphere of dwelling rooms. Alpha-activities due to radon, thoron and their decay products, were evaluated for the determination of the detection efficiencies of the SSNTD utilized for the emitted a-particles by measuring the corresponding track densities. The influence of the ventilation rate and building material on the concentration of radon, thoron and their progenies was investigated. Equilibrium factors between radon and its progeny and between thoron and its daughters have been evaluated in the air of the rooms.     

Evaluating the potential alpha energy of radon progeny

Potential alpha energy concentration of radon progeny can be measured using the alpha-spectroscopy with the silicon semiconductors detectors and the gross-counting attached with the ZnS detectors. The decay method was applied where the alpha particles emitted from the ²¹⁸Po to ²¹⁴Po were detected. In the case of the decay products, the amount and aerodynamic behavior of radioactivity are important, and also need to be measured. During the experiment, the radon gas was supplied and evaluated from the experimental room with constant concentration. Then the air sample was used as the known volume and the grab sampling technique was developed for estimating the concentration of radon decay products. However the proper calculation was applied for estimating the potential alpha energy of radon progeny through of ²¹⁸Po, ²¹⁴Pb and ²¹⁴Bi.     

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.     

Field measurement of the <Superscript>218</Superscript>Po, <Superscript>214</Superscript>Pb and <Superscript>214</Superscript>Bi concentrations in typical indoor and outdoor environments in Beijing

The activity concentrations of ²¹⁸Po, ²¹⁴Pb and ²¹⁴Bi [i.e. C(²¹⁸Po), C(²¹⁴Pb), and C(²¹⁴Bi)] and the calculated concentration ratios [i.e. 1:C(²¹⁴Pb)/C(²¹⁸Po):C(²¹⁴Bi)/C(²¹⁸Po)] are necessary for assessing radon and its progenies exposure. In this study, a measurement method of radon progenies concentrations with both high sensitivity and low uncertainty, was developed based on the Kerr method. The field measurement results of radon progeny concentrations and calculated concentration ratios in both typical indoor and outdoor environments in Beijing, China, were reported. The effects of air exchange rate on concentration ratios of radon progenies in indoor environments were discussed.     

A continuous monitor for assessment of 222Rn in the coastal ocean

Radon-222 is a good natural tracer of groundwater flow into the coastalocean. Unfortunately, its usefulness is limited by the time consuming natureof collecting individual samples and traditional analysis schemes. We demonstratehere an automated system which can determine, on a continuousbasis, the radon activity in coastal ocean waters. The system analyses ²²²Rn from a constant stream of water passing through an air-water exchangerthat distributes radon from the running flow of water to a closed air loop.The air stream is feed to a commercial radon-in-air monitor which determinesthe concentration of ²²²Rn by collection and measurement of theemitting daughters, ²¹⁴Po and ²¹⁸Po, via a charged semiconductordetector. Since the distribution of radon at equilibrium between the air andwater phases is governed by a well-known temperature dependence, the radonconcentration in the water is easily calculated.     

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.     

The initial atmospheric behavior of radon decay products

The chemical and physical properties of²¹⁸Po immediately following its formation from²²²Rn decay are important in determining its behavior in indoor atmospheres and play a major part in determining its potential health effects. In 88% of the decays, a singly charged, positive ion of²¹⁸Po is obtained at the end of its recoil path. These ions can interact with water vapor or other volatile organic compounds (VOCs) that may exist in indoor air. The ions can be neutralized by 3 different mechanisms, small-ion recombination, electron transfer, and electron scavenging. In typical indoor air, the ion will be rapidly neutralized by transfer of electrons from lower ionization potential gases such as NO₂. The neutral molecule can then become incorporated in ultrafine particles formed by the radiolytic processes in the recoil path. These particles will typically be formed by the presence of the air ions produced by the passage of the emitted -particle through ion-induced nucleation. In addition these energetic ions can react with water molecules to produce hydroxyl radicals. Thus, the decay of the radon nucleus produces a variety of effects and can result in changes in the size of the radioactive species that includes the radon progeny.     

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.     

Fast determination of indoor radon (<Superscript>222</Superscript>Rn) concentration using liquid scintillation counting

The indoor ²²²Rn radionuclide was directly absorbed in typical 20 ml glass scintillation vials by passing ?3 dm³ of ambient air through 16 ml of water-immiscible non-volataile scintillation cocktail Ultima-Gold F for 10 min. The activity of radon and its two α-emitting daughters: ²¹⁸Po and ²¹⁴Po, was determined with the BetaScout low-background liquid scintillation counter. The limit of ²²²Rn detection is 9 Bq/m³, and the quantification limit with 20% relative accuracy is 28 Bq/m³. The results of the indoor Rn measurement in different houses showed good consistency with results obtained from a Sarad EQF 3220 device.     

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.     

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.     

Detection efficiency improvement of a large volume scintillation cell

A large volume scintillation cell (LVSC) for radon activity concentration measurements has been reported at MARC-IV. The present paper describes improvements in the detection efficiency of the LVSC and results of the radon activity concentration measurements for indoor air that were performed using the improved LVSC. The cell is a cylindrical shape and has two photomultiplier tubes that are attached to a condensing lens on the photocathode so as to provide good light collection. Individual counting efficiencies were determined to be 0.48 for ²²²Rn, 0.55 for ²¹⁸Po, and 0.61 for ²¹⁴Po. The average counting efficiency per alpha-particle from the radon and its short half-life progenies was 0.55. This value is smaller than the original value reported by LUCAS of 0.86. However, the sensitivity is approximately eight times higher than that of the Lucas cell, which has a smaller volume. A background counting rate of 0.015 cps was obtained. The lower limit of detection (LLD) for the measurements was estimated using the average background counts, the detection efficiency and measurement time. The LLD at 80% statistics confidence limits was less than 10 Bq/m³ when counted within two hours.     

Field alpha-spectroscopy of radon (<Superscript>222</Superscript>Rn) and actinon (<Superscript>219</Superscript>Rn) progeny in soil gas: Locating a radon source

Summary The activities of²¹⁸Po,²¹⁴Po and²¹¹Bi were determined in samples obtained of soil/gas. Sampling work was taken in Jáchymov (Czech Republic) at the outcrop of the Geister-vein,by electrostatic precipitation from filtered soil gas on stainless steel disks.The samples were measured in a field laboratory using a semi-conductor alpha-spectrometer.The activities of²¹⁸Po,²¹⁴Po and²¹¹Bi were calculated.Samples taken from active dump material (near-by radon source) exhibited a high²¹¹Bi/²¹⁴Po ratio, while those of the vein outcrop (a relatively deeper source) had a low ratio.A mathematical model was employed to determine the radon age calculated from the actinon/radon input ratio.This varied in a range of 5.6 to -7.7 seconds.Negative age values are probably caused by the preference for actinon, which rapidly comes into equilibrium with the source of this gas.     

Determination of atmospheric lead-210 by alpha-scintillation counting of air filters

Alpha-counting of filters used to sample large volumes of air provides a convenient way of determining atmospheric concentrations of²¹⁰Pb. Following decay of short-lived²²²Rn and²²⁰Rn progeny, alpha activity of the filters increases as²¹⁰Pb decays to²¹⁰Po. After transient equilibrium is reached at about 3 y, alpha activity diminishes with the 22.3 y halflife of²¹⁰Pb. The degree of equilibrium between²¹⁰Pb and²¹⁰Po can be calculated subsequent to sampling, and the average concentration of²¹⁰Pb in the air during the sampling period can be computed. Contributions to the total²¹⁰Pb from ambient short-lived radon progeny are small, typically 2–4%. Using high volume air samplers with collection rates of 1.1–1.7 m³/min for 24 h periods, and using counting times of 2 h for 20 cm² filter sections, we measured alpha counts ranging from 0.0100±0.0050 to 0.200±0.0200 dps. Periodic measurements on 100 of these filters over a 4 y period yielded mean²¹⁰Pb levels with standard deviations less than ±15%. The method requires minimal sample preparation and can be used to determine past atmospheric²¹⁰Pb concentrations on filters stored for up to 20 y and more.     

Radon and thoron progeny levels in air samples at Udagamandalam region of Nilgiris in India

Measurement of concentration of radon and thoron daughter products in various indoor environment covering four seasons of a year in Udagamandalam Taluk of Nilgiris biosphere has been carried out using a high volume air sampler to asses the inhalation dose to the population which delivers higher dose than the radon and thoron gas alone. The potential alpha-energy concentrations of the radon and thoron progeny ranged from 0.97 to 12.72 mWL and from 1.63 to 15.83 mWL with a geometric mean of 6.02 and 7.89 mWL, respectively, taking all seasons into account. These measurements have yielded a wealth of data on the variation among the indoor radon and thoron progeny in various places during different seasons. The radon and thoron progeny levels are higher in winter seasons and are less in summer season with autumn and spring data lie in between winter and summer. Using the dose conversion factor for indoor exposures given in UNSCEAR 93 report the internal equivalent dose to the inhalation of radon progeny is evaluated to be 1357 mSv^.y^–1 and the corresponding annual effective dose equivalent value has been found to be 2.13 mSv^.y^–1. It can be observed that the mean value of radon is higher than the Indian average. Also it is found the radon and thoron progeny levels are higher in the case of houses built with rock and granite and in tiled type houses of nearly 100 years old. The levels are less in the case of houses built with brick and cement. The observed results for different types of houses and seasons are discussed in this paper.     

Depth dependent study of radon, thoron and their progeny in tube-wells

Radon has been recognized to be one of the major contributors to the natural radiation causing even lung cancer if it is present at enhanced levels. Its monitoring at highly confined locations such as underground caves, mines and tube-wells is very essential for finding the health related hazards among the workers. This paper reports the investigations of the levels of radon, thoron and their progeny monitored in the tube-wells of the Halls of residence at A.M.U., Aligarh, which lies in the subtropical region of Indo-Gangetic plains situated in North India. The twin cup dosimeters were fixed for exposure at a depth of 5?C35?feet with a difference of 5?feet from the ground surface. The values of radon and thoron concentrations were found to vary from 6.58 to 1218.57 and 7.41?C3226.61?Bq?m^?3, respectively. The preliminary results of this study for ??bare mode?? detectors have been separately published and compared with the recent data.     

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.     

Development of measurement system for adsorption of long-lived radon decay products on the leaf surface of tobacco plants

Our previous studies indicated the suitability of tobacco plants for biomonitoring remediated depositories, due to their ²¹⁰Po and ²¹⁰Pb accumulation ability. The methods and requirements of testing ²¹⁰Pb uptake by leaf-surface adsorption was investigated and implemented in the construction of a controlled environment. Uranium ore (theoretical Rn concentration 638 Bqm^?3) was the main source of radon and progeny. Rn concentrations were measured by RAD7, AlphaGUARD, EQF 3220, RTM 2100 and CR-39 SSNTDs (411–516 Bqm^?3). Activity concentrations of the attached and unattached fractions were determined by EQF 3220. The results are indicative of good measurement setup for tracking ²¹⁰Po(Pb) uptake pathways.     

Assessment of inhalation exposure potential of broken uranium ore piles in low-grade uranium mine

This paper presents the assessment of inhalation exposure potential of broken uranium ore piles in different stopes of Jaduguda uranium mines of India. ²²²Rn emanation coefficient of broken uranium ore was measured in laboratory by collecting air sample from airtight glass jar containing ore sample. An attempt was also made to correlate the emanation coefficient with ²²⁶Ra content of the ore. The ²²²Rn progeny doses estimated based on radon activity concentration of broken ore, occupancy period and equilibrium ratio in different stopes were well below the prescribed limit of International Commission on Radiological Protection. The maximum ²²²Rn progeny dose contribution from broken ore piles was worked out to be 0.22 mSv year^?1. This suggests that the broken ore piles are not the significant contributor of inhalation exposure under the existing ventilation condition of Jaduguda uranium mine.     

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.