Characterisation of an electronic radon gas personal dosemeter

The monitoring of radon exposure at workplaces is of great importance. Up to now passive measurement systems have been used for the registration of radon gas. Recently an electronic radon gas personal dosemeter came onto the market as an active measurement system for the registration of radon exposure (DOSEman; Sarad GmbH, Dresden, Germany). In this personal monitor, the radon gas diffuses through a membrane into a measurement chamber. A silicon detector system records spectroscopically the alpha decays of the radon gas and of the short-lived progeny 218Po and 214Po gathered onto the detector by an electrical field. In this work the calibration was tested and a proficiency test of this equipment was made. The diffusion behaviour of the radon gas into the measurement chamber, susceptibility to thoron, efficiency, influence of humidity, accuracy and the detection limit were checked.     

Effects of thoron on a radon detector of pulse-ionization chamber type

A radon detector of pulse-ionization chamber (PIC) type could have some sensitivity for thoron. Thus, the presence of thoron could interfere with precise measurement of radon. In the present study, effects of thoron on the most common type of PIC detector (commercial name AlphaGUARD) were investigated using an exposure chamber. The AlphaGUARD was exposed to a mixture of radon and thoron, together with a radon/thoron discriminative monitor that employs a silicon solid-state detector. The thoron sensitivity of the PIC detector was estimated by comparing the two detectors. As a result, the thoron sensitivity was about 10% compared with the radon sensitivity. In other words, the radon concentration (Bq m(-3)) measured with the PIC detector was approximately the sum of the actual radon concentration (Bq m(-3)) and 10% of the thoron concentration (Bq m(-3)). The sensitivity to thoron should be considered in measurements in thoron-enhanced areas.     

Instrument performance of a radon measuring system with the alpha-track detection technique

An instrument performance test has been carried out for a radon measuring system made in Hungary. The system measures radon using the alpha-track detection technique. It consists of three parts: the passive detector, the etching unit and the evaluation unit. A CR-39 detector is used as the radiation detector. Alpha-track reading and data analysis are carried out after chemical etching. The following subjects were examined in the present study: (1) radon sensitivity, (2) performance of etching and evaluation processes and (3) thoron sensitivity. The radon sensitivity of 6.9 x 10(-4) mm(-2) (Bq m(-3) d)(-1) was acceptable for practical application. The thoron sensitivity was estimated to be as low as 3.3 x 10(-5) mm(-2) (Bq m(-3) d)(-1) from the experimental study.     

Development of a new thoron progeny detector based on SSNTD and the collection by an electric field

The importance of (220)Rn (thoron) progeny for human exposure has been widely recognised in the past decades. Since no stable equilibrium factor was found between indoor thoron and its progeny, and the concentration of thoron progeny varies with time, it is necessary to develop detectors for long-term measurement that directly sample and detect thoron progeny. However, power supply of this kind of detectors has always been a problem. In this study, a set of device that is suitable for long-term measurement is introduced. A high-voltage electric field was formed for the collection of charged aerosols attached by (222)Rn (radon) and thoron progenies on solid-state nuclear track detector. Impact from radon progeny could be eliminated with a shield of Al foil of appropriate thickness. Tests were made both in an experimental house and in a thoron chamber in Helmholtz Zentrum München to determine the parameters and to verify the universality under different conditions.     

An extensive indoor 222Rn/220Rn monitoring in Shillong, India

The behaviour of ubiquitous radon (222Rn), thoron (220Rn) and their progeny in the indoor atmosphere generally reflects a complex interplay between a number of processes, the most important of which are radioactive alpha-decay, ventilation, attachment to aerosols and deposition on surfaces. The present work involved a long-term (1997-2000) passive monitoring of 222Rn and 220Rn in the indoor environment of Shillong, Meghalaya. The north-east region of India being a zone of high seismicity, the indoor radon and thoron map of the region will provide a better insight and a valuable database for any study related to radon and thoron anomalies.     

A passive radon dosemeter suitable for workplaces

The results obtained in different international intercomparisons on passive radon monitors have been analysed with the aim of identifying a suitable radon monitoring device for workplaces. From this analysis, the passive radon device, first developed for personal dosimetry in mines by the National Radiation Protection Board, UK (NRPB), has shown the most suitable set of characteristics. This radon monitor consists of a diffusion chamber, made of conductive plastic with less than 2 cm height, containing a CR-39 film (Columbia Resin 1939), as track detector. Radon detectors in workplaces may be exposed only during the working hours, thus requiring the storage of the detectors in low-radon zones when not exposed. This paper describes how this problem can be solved. Since track detectors are also efficient neutron dosemeters, care should be taken when radon monitors are used in workplaces, where they may he exposed to neutrons, such as on high altitude mountains, in the surroundings of high energy X ray facilities (where neutrons are produced by (gamma, n) reactions) or around high energy particle accelerators. To this end, the response of these passive radon monitors to high energy neutron fields has been investigated.     

Collaborative investigations on thoron and radon in some rural communities of Balkans

This paper deals with the results of the first-field use in the Balkans, i.e. Serbia and Republic of Srpska (Bosnia and Hercegovina), of a passive polycarbonate Mark II type and poliallyldiglycol carbonate (Cr-39) alpha track detectors sensitive to thoron as well as to radon. Both types of solid state nuclear track detectors were designed and supplied by National Institute of Radiological Sciences (NIRS), Chiba, Japan. The commercial names for these detectors which all have been field tested in Balkan rural communities are known as: UFO and RADUET passive discriminative radon/thoron detectors. No database of thoron and thoron progeny concentrations in dwellings in Serbia or Balkans region exist, and as a result, the level of exposure of the Serbian population to thoron and its progeny is unknown so far.     

Influence of environmental changes on integrating radon detectors: results of an intercomparison exercise

An intercomparison exercise for passive integrating radon detectors has been carried out with the participation of 12 detection systems from 10 laboratories. The detection systems comprise three commonly used in radon integrating measurements, tracks, activated charcoal canisters and electrets. The exposures were carried out in the radon and thoron chambers at the Institute of Energy Techniques (INTE) of the Technical University of Catalonia (UPC), which is considered to be the Spanish reference chamber. The detectors were exposed to three different temperatures (10, 20 and 30 degrees C) and relative humidities (30, 45 and 80%). Furthermore, in three exposures radon concentration was drastically changed during the exposure period in order to study the efficiency of canister collection. The results indicated that only the charcoal canister response was found to be significantly influenced by external climatic conditions and radon fluctuations. Those track detectors, which are unable to measure thoron concentrations show thoron sensitivity and thus interfere with precise measurement of radon. Detectors for measuring thoron concentration show quite a different response, which could be related to their traceability.     

Detection properties of a measuring system for a continuous soil radon concentrations monitoring.

The continual soil-gas radon concentration measurements are absolutely crucial for a reliable assessment of radon entry characteristics into the indoor building environment. For this purpose, a new detection system (a continuous monitor RM-3) was developed and tested. The detection principle of the monitoring device is based on an airflow ionisation chamber operating in a current mode. A comprehensive series of testing and calibration experiments have been carried out in a laboratory environment. An output signal of the device caused by the radon concentration in a sensitive detection volume significantly depends on a detector ventilation rate, the gas flow rate through the ionisation chamber. A set of calibration experiments was accomplished with the artificial radon source application and close circuit experimental arrangements. The system detection properties including applied experimental conditions and key results of pilot in situ measurements are reported in detail.     

Mimicking lung dose by wire-mesh-capped deposition sensors: a new dosimetric strategy of radon (thoron) decay products

The dose conversion factor (DCF) of radon decay products may vary by a factor of ～40 within the particle size range from ～0.5 nm to tens of micrometres. An ideal detector should have a response, which closely mimics the strong dependence of the DCF on the particle size. This dependence is essentially determined by the different deposition rates of the particles with different sizes on the trachea-bronchial tree and alveoli. These deposition rates versus the particle sizes are similar to those of the decay products onto indoor surfaces. These conclusions are conducive to a new strategy for the dosimetry of radon (thoron) decay products, which is simply based on the detection of decay products deposited on flat surfaces. The dependence of the deposition rate of radon decay products onto flat surfaces versus the particle size is necessarily different from that of the deposition rate on the trachea-bronchial region, especially for particle sizes smaller than a few nanometres and larger than a few micrometres. In the present work, in order to obtain a better mimic between the measurement of flat-surface-deposited radon (thoron) decay products and the DCF at any given particle size, a suitable screen is placed against the surrogate surface, used for the assessment of the radon (thoron) decay products deposition.     

Survey of radon and thoron in homes of Indian Himalaya

Measurements of radon, thoron and their progeny were carried out in some houses from Garhwal and Kumaun Himalayas of India using a LR-115 plastic track detector. The measurements were made in various residential houses of the area at a height of 2.5 m above the ground level using a twin chamber radon dosemeter, which can record the values of radon, thoron and their progeny separately. The concentrations of radon and thoron in these homes were found to vary from 11 to 191 and 1 to 156 Bq m(-3), respectively. The equilibrium factor between radon and progeny varies from 0.02 to 0.90, with an average of 0.26 for the region. The resulting dose rate due to radon, thoron and their decay products was found to vary from 0.02 to 0.84 μSv h(-1) with an arithmetic mean of 0.27 μSv h(-1). A detailed analysis of the distribution of radon, thoron and their decay products inside a house is also reported. The observed dose rates due to radon, thoron and progeny were found somewhat higher but well below the international recommendations.     

Sensitive method for the determination of F attached to aerosol particles in a PET centre

A new grab sampling method has been developed for the measurement of ¹⁸F attached to aerosol particles. It is based on direct β-counting of filtered aerosol sample over successive time intervals by an end-window Geiger–Müller counter. The effect of the progeny of radon and thoron on the β-counting rate is separated by analysing the decay curve. The defined solid angle absolute counting was used to evaluate the efficiencies for ¹⁸F and for the progeny of radon and thoron one by one. Absolute activity concentration of ¹⁸F can be determined with less than 10% systematic error. Glass-fibre filter and high sampling flow rate are applied, leading to a detection limit for ¹⁸F of less than 1 Bq m⁻³. The method was tested under different circumstances in the PET centre of University of Debrecen, Hungary.     

Field comparison of two different passive radon detectors

The present paper describes field performance of two different passive radon monitor devices formed, respectively, by a CR-39 track detector enclosed in a diffusion chamber and a cellulose nitrate detector (LR-115) in a heat-sealed polyethylene bag. The most important scope of these investigations was to study the performance of these detectors directly in the field. To this end, two different types of radon monitors mentioned above have been exposed simultaneously in 100 school rooms within the Italian region Friuli Venezia Giulia. Finally, the accuracy of their responses has been evaluated by exposing them under extreme humidity conditions and/or together with other radon measurement instruments.     

Thoron measurements in Hungary

In this study, several Hungarian dwellings and working places were surveyed using passive radon- and thoron-measuring devices (Radopot(?) and Raduet(?)) from 2003 to 2008. The detectors were placed 15-30 cm from the wall throughout the 1- to 3-month period. In dwellings, the presence of thoron, ～100 Bq m(-3), was detected almost in all cases, ; however, in the cellars of these buildings, a value ～200 Bq m(-3) was typical. In the cases of manganese and bauxite mines, the concentration of thoron was mainly 200 and 500 Bq m(-3), respectively. In caves, it was 1000 Bq m(-3), whereas in the radon bath it was ～100 Bq m(-3). As in many cases, the ratio between thoron and radon concentrations was >0.25 and the dose contribution from thoron and its progeny was not negligible. Therefore, further investigation on the thoron progeny will be necessary for an accurate dose estimation.     

Influence of environmental changes on continuous radon monitors. Results of a Spanish intercomparison exercise

The first Spanish intercomparison exercise for continuous radon monitors was carried out with the participation of nine monitoring systems from eight laboratories. The exposures were carried out in the radon and thoron chambers at the Institute of Energy Techniques (INTE) of the Technical University of Catalonia (UPC), which is considered to be the Spanish reference chamber. The monitors were exposed to three different temperatures (13, 20 and 30 degrees C), relative humidities (30, 45 and 80%) and radon concentrations (450, 2000 and 9000 Bq m(-3)). Exposures in the thoron chamber were carried out at concentrations of approximately 450 Bq m(-3). The response of the ionisation chambers and scintillation monitors was acceptable. However, the response of monitors based on electrostatic collection was found to be influenced by external climatic conditions. Moreover, all radon monitors were sensitive to thoron concentration, which was especially significant for scintillation monitors.     

Development and application of a needle trap device for time-weighted average diffusive sampling

A simple, cost-effective analysis combining solventless extraction, thermal desorption, and determination of volatile organic compounds (VOCs) was developed and validated. A needle trap device (NTD) packed with the sorbent Carboxen1000 was used as a time-weighted average (TWA) diffusive sampler to collect target compounds by molecular diffusion and adsorption to the packed sorbent. This process can be described with derivations of Fick's first law of diffusion, which expresses the relation between the TWA concentrations to which the passive sampler is exposed and the mass of analytes adsorbed to the packed sorbent in the sampler. The effects of experimental factors such as temperature, pressure, humidity, and face velocity were taken into account in applying diffusive sampling under nonideal conditions. This study demonstrates that NTD is effective for air analysis of benzene, toluene, ethylbenzene, and o-xylene (BTEX), due to the good adsorption/desorption quality of Carboxen 1000 and to the special geometric shape of the needle with a small cross section avoiding the need for calibration. Storage tests showed good storage stability for BTEX. Verification of the theoretical model showed good agreement between theoretical and experimental sampling rates. Method validation done against NIOSH method 1501, SPME, and NTD active sampling revealed good agreement between those methods. Automated NTD sample introduction to a gas chromatograph facilitates the use of this technology for industrial hygiene applications.     

An automated multisensor apparatus for comparative membrane radon and thoron permeability studies

An apparatus has been designed to investigate the permeability characteristics of membranes to radon and thoron. The apparatus consists of a number of radon gas passive monitors and meteorological sensors, interfaced to a programmable data acquisition system (data logger). The system is fully automated, and hence, operates unattended for long periods of time. Because the apparatus features a multisensor system, simultaneous permeability studies of up to 11 different membranes is possible, thereby simplifying permeability studies considerably, resulting in a dramatic saving in time. The theory on which the experimental determination of membrane permeability is based, is presented. Furthermore, some experimental work conducted with several membranes is presented and discussed.     

Long-term measurements of thoron, its airborne progeny and radon in 205 dwellings in Ireland

Long-term (circa 3 months) simultaneous measurements of indoor concentrations of thoron gas, airborne thoron progeny and radon were made using passive alpha track detectors in 205 dwellings in Ireland during the period 2007-09. Thoron progeny concentrations were measured using passive deposition monitors designed at the National Institute of Radiological Sciences (NIRS), Japan, whereas thoron gas concentrations were measured using Raduet detectors (Radosys, Budapest). Radon concentrations were measured in these dwellings by means of NRPB/SSI type alpha track radon detectors as normally used by the Radiological Protection Institute of Ireland (RPII). The concentration of thoron gas ranged from <1 to 174 Bq m(-3) with an arithmetic mean (AM) of 22 Bq m(-3). The concentration of radon gas ranged from 4 to 767 Bq m(-3) with an AM of 75 Bq m(-3). For radon, the estimated annual doses were 0.1 (min), 19.2 (max) and 1.9 (AM) mSv y(-1). The concentration of thoron progeny ranged from <0.1 to 3.8 Bq m(-3) [equilibrium equivalent thoron concentration (EETC)] with an AM of 0.47 Bq m(-3) (EETC). The corresponding estimated annual doses were 2.9 (max) and 0.35 (mean) mSv y(-1). In 14 or 7% of the dwellings, the estimated doses from thoron progeny exceeded those from radon.     

Thoron and decay products, beyond UNSCEAR 2006 Annex E

Uranium and thorium series radionuclides are present in all soils and rocks. Thus, radon and thoron, the radioactive noble gases originating in the uranium ((238)U) and thorium ((232)Th) decay chains is ubiquitous and everyone is exposed to both radon and thoron gases and their particulate radioactive decay products. As described in UNSCEAR Annex E (2006), radon and its decay products have been recognised for many years as a hazard to underground miners. More recently, the risks from exposure to residential radon have been demonstrated through residential case-control epidemiological studies. However, as discussed by UNSCEAR, exposures to thoron and its decay products have often been relatively ignored. Moreover, unlike radon the effects of exposure to thoron and its decay products are not available from epidemiology and thus, a dosimetric approach is required to assess risks. UNSCEAR continues to recommend the use of a dose conversion factor for thoron decay products of 40 nSv (Bq h m(-3))(-1). UNSCEAR Annex E suggests there is an emerging problem, namely, that the contribution of (220)Rn (thoron) gas to the (222)Rn (radon) gas measurement signal is not well known. Until recently, this has largely been ignored. This is an important consideration as measurements at work and homes are the basis for investigating lung cancer exposure-response relationships. Based on UNSCEAR Annex E, this paper provides an overview of the sources and levels of thoron and its associated decay products at home and work. In addition, this paper provides an overview of the thoron dosimetry considered by UNSCEAR Annex E and some recent results.     

CFD modelling of thoron and thoron progeny in the indoor environment

Thoron (220Rn) exhalation from building materials has become increasingly recognised as a potential source for radiation exposure in residences. However, contrary to radon (222Rn), limited information on thoron exposure is available. The purpose of this study is to estimate the concentration of thoron and its progeny products in a typical Dutch living room using computational fluid dynamics. The predicted thoron concentration is ～9 Bq m(-3) using a source term of 14 Bq s(-1) for the thoron exhalation from building materials. The concentration varies from 15 Bq m(-3) near the building materials to 2.7 Bq m(-3) in the centre of the living room. The mean effective dose from thoron progeny is calculated as 0.09 mSv y(-1), with a total effective dose from radon and thoron progeny of 0.38 mSv y(-1).