Results of the 2010 National Radiation Protection Institute intercomparison of radon and its short-lived decay product continuous monitors

During the Sixth European Conference on Protection Against Radon at Home and at Work held in autumn 2010 in Prague, the first intercomparison of continuous radon and its short-lived decay product monitors was organised and held by the Natural Radiation Division of the National Radiation Protection Institute (NRPI) in Prague. Eight laboratories submitted eight continuous radon monitors, two electronic monitors, three passive integral systems based on charcoal and three continuous radon short-lived decay product monitors. The intercomparison included exposures to both the radon gas concentration and equivalent equilibrium radon concentration (EEC) under different ambient conditions similar to the ones in dwellings. In particular, the influence of the equilibrium factor F, unattached fraction of EEC f(p) and absolute air humidity were investigated. The results of the radon gas measurements were performed on a calibration level of about 8 kBq m(-3). The results of all monitors were compared with the reference NRPI monitor.     

Are radon gas measurements adequate for epidemiological studies and case control studies of radon-induced lung cancer?

The lung dose derived from radon is not attributed to the radon gas itself, but instead to its short-lived progeny. However, in many epidemiological studies as well as in case control studies of the radon risk, the excess number of cancers are related to the radon gas exposure, and not to the radon progeny exposure. A justification for such an approach has resorted to the assumption that there is self-compensation between the radiation doses from the unattached and attached fractions. In the present study, we used the Jacobi model to calculate the radon progeny concentrations in a room by varying the attachment rate and then calculated the resulting lung dose. It was found that self-compensation was not fully realised, and the effective dose can vary by a factor up to approximately 2 for the same radon gas concentration. In conclusion, the radon gas concentration alone does not provide adequate information on the effective dose.     

Influence of radioactive aerosol and biological parameters of inhaled radon progeny on human lung dose

The present work focuses on assessing the influence of biological and aerosol parameters on human lung dose. The dose conversion factor (DCF), which gives the relationship between the effective dose and the potential alpha energy concentration of inhaled short-lived radon progeny (218Po, 214Pb, 214Bi/214Po) is estimated using a dosimetric approach related to the International Commission on Radiological Protection(ICRP). The calculations are based on the measurements of the distribution of activity size of indoor radon progeny, their unattached fraction (f(b)) and potential alpha energy concentration (E). These experimental data are measured using a low-pressure cascade impactor and a wire-screen diffusion battery. Because of the short half-lives of the investigated nuclides, modifications that simplify the dose calculation are possible. The radioactive aerosol and biological parameters are varied in order to assess the DCF arising from the uncertainty of these parameters. The main emphasis is on the variation of the ventilation rate, breathing mode, critical cells for the induction of lung cancer and the parameters of the attached and unattached activity size distribution of the radon progeny. The investigation shows that the DCF is more than a factor of two higher than the values recommended by the ICRP, namely 3.9 mSv WLM(-1) for the public and 5.1 mSv WLM(-1) for working places. The dose results for indoor aerosol conditions are in the range 2.3-2.6 mSv WLM(-1) depending on the breathing mode.     

Evaluation and comparison of measurements of unattached and attached radon progeny in the radon chamber of PTB Braunschweig (Germany) with NRPI Praha (Czech Republic)

On the case of a parallel metrological measurement of unattached and attached concentrations of radon progeny, the evaluation by an inversion of the Jacobi-Porstend?rfer room model indicates a real overestimation of the concentration of RaA ((218)Po).     

Monitoring of short-lived radon progeny in mines

Obligatory measurements of the potential alpha energy concentration of short-lived radon progeny have been performing in the Polish underground mines since 1989. In consideration of economic aspects, an attempt was made from the very beginning to combine it with measurements of the dust concentration. Therefore the developed measuring units were an integral part of the dust samplers complying with the requirements of the State Mining Authority to apply them in underground mines. This way the developed devices could fulfil two measurement tasks simultaneously: measurement of the dust concentration and potential alpha energy concentration of short-lived radon progeny. The new device based on the thermoluminescence detectors is able to cooperate with the dust samplers made by the SKC company and equipped with a cyclone making it possible to operate them constantly for one working day. The lower limit of detection was equal about 0.04 microJ m(-3) at a 95% confidence level and 1 h pumping.     

Interlaboratory comparisons for passive radon measuring devices at BfS

Since 2003, the German Federal Office for Radiation Protection (BfS) has conducted annual interlaboratory comparisons for passive radon measuring devices in order to ensure the quality of these measurements. Passive radon devices which use solid state nuclear track detectors, electrets or activated charcoal can be tested. The exposures of radon devices are carried out in the radon calibration laboratory at BfS. Radon activity concentrations are traced back to the national standard, being established at the National Institute of Physics and Metrology (PTB). According to the national guideline, radon services which offer radon monitoring at workplaces have to participate in the intercomparisons and prove the suitability of their radon devices for the measurements.     

A chamber to test the response of radon detectors to changing environmental conditions

Radon risk assessment is carried out by means of accurate measurements with active or passive instrumentation. All radon detectors must be calibrated and tested using a radon chamber containing a known concentration of radon produced by specific sources of (226)Ra. Some chambers can also be used to test the response of detectors as a function of environmental conditions. In this case, a calibration curve can be inferred with respect to change in one of the considered parameters. For this aim, a new radon chamber was designed and realised to perform calibration and to study the detector response in a large range of variation of the environmental parameters (pressure, 700-1100 mbar; temperature, 5-50°C; humidity, 10-90 %). The first experiments conducted to study the influence of environmental parameters on the detector response have shown flexibility and ease of use of the chamber.     

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.     

Influence of variability of 214Pb recoil factor on lung dose

Different parameters enter models of the human respiratory tract. The unattached fraction of the radon progeny was identified as the most important parameter, with the strongest influence on lung dose. The unattached fraction depends on the indoor aerosol concentration and other environmental conditions. The recoil factor, p, which influences the unattached fraction of 214Pb and 214Bi, defined as the average detachment probability from the aerosol after an alpha decay of 218Po, has almost always been taken as a constant. Here the recoil factor was recalculated under different assumptions and found to be in the range between 0.1 and 0.8. A smaller recoil factor means lower unattached fractions of 214Pb and 214Bi. The influence of the recoil factor on lung dose was also estimated. The lung dose is smaller by about 10% if p = 0.1 is assumed in calculating the unattached fraction instead of p = 0.8.     

Simultaneous measurements of indoor radon, radon-thoron progeny and high-resolution gamma spectrometry in Greek dwellings

Simultaneous indoor radon, radon-thoron progeny and high-resolution in situ gamma spectrometry measurements, with portable high-purity Ge detector were performed in 26 dwellings of Thessaloniki, the second largest town of Greece, during March 2003-January 2005. The radon gas was measured with an AlphaGUARD ionisation chamber (in each of the 26 dwellings) every 10 min, for a time period between 7 and 10 d. Most of the values of radon gas concentration are between 20 and 30 Bq m(-3), with an arithmetic mean of 34 Bq m(-3). The maximum measured value of radon gas concentration is 516 Bq m(-3). The comparison between the radon gas measurements, performed with AlphaGUARD and short-term electret ionisation chamber, shows very good agreement, taking into account the relative short time period of the measurement and the relative low radon gas concentration. Radon and thoron progeny were measured with a SILENA (model 4s) instrument. From the radon and radon progeny measurements, the equilibrium factor F could be deduced. Most of the measurements of the equilibrium factor are within the range 0.4-0.5. The mean value of the equilibrium factor F is 0.49 +/- 0.10, i.e. close to the typical value of 0.4 adopted by UNSCEAR. The mean equilibrium equivalent thoron concentration measured in the 26 dwellings is EEC(thoron) = 1.38 +/- 0.79 Bq m(-3). The mean equilibrium equivalent thoron to radon ratio concentration, measured in the 26 dwellings, is 0.1 +/- 0.06. The mean total absorbed dose rate in air, owing to gamma radiation, is 58 +/- 12 nGy h(-1). The contribution of the different radionuclides to the total indoor gamma dose rate in air is 38% due to 40K, 36% due to thorium series and 26% due to uranium series. The annual effective dose, due to the different source terms (radon, thoron and external gamma radiation), is 1.05, 0.39 and 0.28 mSv, respectively.     

Uncertainties evaluation for electrets based devices used in radon detection

In recent years uncertainty evaluation in measurements has achievedgreat importance. National and international standards offerguidelines to evaluate uncertainties, but these procedures are,until now, not well understood by the operators. This is becauseof the fact that a detailed uncertainty evaluation is not aneasy operation and a standard rule to apply in all cases isnot available. Every measurement procedure has its own uncertaintyevaluation. In this work, attention is focused upon the electretion chambers (EIC), widely used in radon concentration measurements.Measurements of gamma radiation sensitivity are performed ina secondary standard calibration laboratory and measurementof radon concentration sensitivity is performed in a radon chamber0.8 m³ in volume. Raw data are analysed to evaluate the calibrationfactors and the combined uncertainties are determined. The aimof the work is to give a practical method to assess the uncertaintyof a radon measurement.     

Fraction of the positive 218Po and 214Pb clusters in indoor air

The fraction of the positively charged unattached radon decay products, 218Po and 214Pb in indoor air was determined by model calculations. The results of the calculations were confirmed by measurements in a test chamber (volume: 8 m3). The fraction of both radionuclides depends on the attachment parameter (S(1)) and the neutralisation rate (nu) in room air. The total removal parameter S1 = lambda1 + v + q(f) + X = lambda1 C1f/C0 considers the attachment rate to aerosol particles (X), plate-out rate to room surfaces (q(f)) and the ventilation rate (nu) (lambda1: decay constant of 218Po). The S1-value of room can be determined by measurement of the concentration of the unattached 218Po clusters (C1f) and radon (C0). The neutralisation rate (nu) in environmental air depends mainly on the ion production rate. The influence of the relative humidity in the range 30-95% (temperature: 20 degrees C) is negligible. In addition, equal neutralisation rates for 218Po and 214Pb could be derived. In room air with ion production rates between 5 and 500 nC kg(-1) h(-1) mainly generated by the alpha emitters of radon, thoron and their short-lived decay products, the fractions for positive 218Po clusters vary between 55 and 17% and for 214Pb clusters between 53 and 14%. For a typical average concentration of radon (50 Bq m(-3)) and thoron (10 Bq m(-3)) in homes, 48% of 218Po clusters and 45% of 214Pb clusters are positively charged.     

Experimental determination of the absorption rate of unattached radon progeny from respiratory tract to blood

An exposure methodology was developed for the determination of the absorption rate of unattached radon progeny deposited in the human respiratory tract to blood. Twenty-one volunteers were exposed in a radon chamber during well-controlled aerosol and radon progeny conditions, with predominantly unattached radon daughters. Special efforts were made to restrict the dose to the volunteers to an absolute maximum of 0.08 mSv. Measurements of radon gas and radon progeny in blood samples of these volunteers indicated absorption half times of 20 min to 60 min. Former determinations, mainly performed with much larger aerosol particles of diameters between 100 nm and 1,000 nm, implied absorption half times around 10 h. This indicates that the absorption of radon decay products from ciliated airways into blood is dependent upon particle size and particle composition.     

A Calibration and Quality Assurance Program for Environmental Radon Measurements

The ideal facility for assessing the quality of radon measurements at environmental levels consists of: (1) an instrument whose response to radon and its progeny is determined from measurements of a certified or standard ²²⁶Ra source, and (2) a calibration room with a known radon concentration.The linkage between these two elements and additional quality control requirements are discussed here for some Environmental Measurements Laboratory radon measurements programs.     

Radon monitor calibration using NIST radon emanation standards: steady flow method

The National Institute of Standards and Technology (NIST) polyethylene-encapsulated 226Ra/222Rn emanation (PERE) standards (old SRM 4968 and new SRMs 4971, 4972, and 4973) provide precise radon emanation rate, certified to a high degree of accuracy (approximately to 2%). Two new SRM 4973 standards containing totally 1036 Bq (0.028 microCi) of 226Ra, emanate 0.114 Bq (3.08 pCi) of 222Rn per min. Air passing over such sources at a flow rate of 1 l min(-1) will have a radon concentration of 114 Bq m(-3) (3.08 pCi l(-1)). This paper describes a practical calibration system and the actual calibration verification data obtained at different flow rates, for E-PERM passive radon monitors, Femto-Tech and Alpha Guard Continuous Radon Monitors. The use of such an affordable and easy to use system by the manufacturers and users of radon measurement devices will bring uniform standards with traceability to a NIST standard source and is considered an important step in standardising radon measurement methods.     

Solid laboratory calibration of a nonimaging spectroradiometer

Field-based nonimaging spectroradiometers are often used in vicarious calibration experiments for airborne or spaceborne imaging spectrometers. The calibration uncertainties associated with these ground measurements contribute substantially to the overall modeling error in radiance- or reflectance-based vicarious calibration experiments. Because of limitations in the radiometric stability of compact field spectroradiometers, vicarious calibration experiments are based primarily on reflectance measurements rather than on radiance measurements. To characterize the overall uncertainty of radiance-based approaches and assess the sources of uncertainty, we carried out a full laboratory calibration. This laboratory calibration of a nonimaging spectroradiometer is based on a measurement plan targeted at achieving a 相似文献   

A self-calibrating radon monitor with statistical discrimination

A radon monitor, able to perform the measurement of the radon and its progeny volumic activity, in a gamma-ray or natural radiation background field, was developed. The instrument consists of a 10 l ionization chamber, a high voltage source, an integrating preamplifier, a data acquisition system and a personal computer. A new method for self-calibration of Radon volumic activity measurements, based on the alpha counting with an ionization chamber is also presented.     

Radon dynamics and reduction in an underground mine in Brazil. Implications for workers' exposure

This work was aimed at studying the behaviour of 222Rn in an experimental underground copper mine in Brazil with a single entrance. The 222Rn concentrations, meaured by using a dynamic radon measuring technique. varied between 30.5 Bq.m(-3), during ventilated conditions applied to the mine galleries, and 19.4 x 10(3) Bq.(-3) for non-ventilated conditions and when operational mining activities were conducted inside. High radon concentration surges were observed after blasting and drilling activities. In the cases of inadequate ventilation, it was estimated that workers could be subjected to exposures as high as 10 microSv.h(-1), only due to 222Rn and its short-lived progeny. The results show the importance of real-time measurements to evaluate radon dynamics during mining operations.     

Comparison of radon lung dosimetry models for the estimation of dose uncertainties

In order to investigate the degree of dose uncertainty produced by different models, three dosimetry models were compared with each other, representing different classes of models: (i) The RADEP/IMBA model based on the ICRP Human Respiratory Tract Model, a deterministic regional compartment model, (ii) the RADOS model, a deterministic airway generation model and (iii) the IDEAL dosimetry model, a stochastic airway generation model. The outputs of the three models for defined mining exposure conditions were compared at three different levels: deposition fractions for attached and unattached radon progeny; nuclear transformations, reflecting the combined effect of deposition and clearance; and resulting cellular doses. Resulting dose exposure conversion factors ranged from 7.8 (median) mSv/WLM (IDEAL) to 11.8 mSv/WLM (RADEP/IMBA), with 8.3 mSv/WLM (RADOS) as an intermediate value. Despite methodological and computational differences between the three models, resulting dose conversion factors do not appreciably differ from each other, although predictions by the two generation models are consistently smaller than that for the RADEP/IMBA model.     

Invariants of the Jacobi-Porstendorfer room model for radon progeny in indoor air

The Jacobi-Porstend?rfer room model, describing the dynamical behaviour of radon and radon progeny in indoor air, has been successfully used for decades. The inversion of the model-the determination of the five parameters from measured results which provide better information on the room environment than mere ratios of unattached and attached radon progeny-is treated as an algebraic task. The linear interdependence of the used equations strongly limits the algebraic invertibility of experimental results. For a unique solution, the fulfilment of two invariants of the room model for the measured results is required. Non-fulfilment of these model invariants by the measured results leads to a set of non-identical solutions and indicates the violation of the conditions required by the room model or the incorrectness or excessive uncertainties of the measured results. The limited and non-unique algebraic invertibility of the room model is analysed numerically using our own data for the radon progeny.