Microdosimetry of inhomogeneous radon progeny distributions in bronchial airways

A Monte Carlo code, initially developed for the calculation of microdosimetric spectra for alpha particles in cylindrical airways, has been extended to allow the computation (i) of additional microdosimetric parameters and (ii) for realistic exposure conditions in human bronchial airways with respect to surface activity distribution and airway geometry. The objective of the present study was to investigate the effects of non-uniform distributions of radon progeny activities in bronchial airways on cellular energy deposition parameters. Significant variations of hit frequencies, doses and microscopic energy deposition patterns were observed for epithelial cell nuclei, depending strongly on the assumed activity distributions. Thus, epithelial cells located at different positions in a given bronchial airway may experience a wide range of biological responses. The results obtained suggest that the hit frequency may be the primary physical parameter for alpha particles, supplemented by microdosimetric single event spectra, to be related to biological effects for chronic low level exposures.     

Bimodal unattached 218Po Radon progeny and the influence of enhanced deposition effect at high-radon levels

Unattached fraction (218)Po airborne particle size distributions from graded screen array diffusion batteries are analysed for bimodal constituents. The analysis is for the high (222)Rn concentration range from 10 to 50 kBq m(-3) where the recently reported enhanced deposition effect is in transition. We find that the single unattached fraction is distributed nominally at an arithmetic mean diameter (AMD) of 0.8-1.0 nm, and consists of two (218)Po molecular species with AMD congruent with 0.756 and 1.101 nm, respectively. In unfiltered room air the 0.756 nm species is the least stable, decreases monotonically in concentration magnitude beginning at 12 kBq m(-3) and disappears completely at approximately 32 kBq m(-3) (at a relative humidity of 54%). The AMD congruent with 1.101 nm mode does not become unstable until it reaches approximately 32 kBq m(-3) (222)Rn level and completely disappears at approximately 50 kBq m(-3). Similar behaviour is observed for filtered air but with some distinct differences. This work supports the bimodal findings for the (218)Po unattached fraction of Porstendorfer and co-workers and provides further details of the high-radon enhanced deposition effect.     

Simulation of the concentrations and distributions of indoor radon and thoron

The technique of computational fluid dynamics (CFD) was used to study the concentrations and distributions of indoor radon (222Rn) and thoron (220Rn) as well as their progeny in three dimensions. According to the simulation results, in a naturally ventilated room, the activity distribution of 222Rn is homogeneous except for the places near air diffuser (supply and exhaust) locations. The concentration of 220Rn exponentially decreases with the distance from the source wall which is considered independently. However, as the ventilation rate increased, the concentrations of both 222Rn and 220Rn decreased and their activity distributions become complicated due to the effect of turbulent flow. It suggests that the impact factors of monitoring conditions (sampling site, airflow characteristics, etc.) should be taken into account in obtaining representative concentrations of 222Rn/220Rn for dose assessment. Both the simulation results of activities and their distributions agreed well with the experimental results in a laboratory room. It suggests that the CFD models may be applicable for the estimation of indoor 222Rn and 220Rn as well as their progeny.     

Study on radon and radon progeny in some living rooms

In the first part of this work, the potential alpha energy concentration (PAEC) of radon progeny, the equilibrium factor (F), the activity concentration of 222Rn gas (Co) and the unattached fraction (fp), were determined in 15 living rooms at El-Minia City, Egypt. The activity size distribution of (214)Pb was measured by using a low pressure Berner impactor. Based on the parameters of that distribution the total effective dose through the human lung was evaluated by using a dosimetric model calculation of ICRP. An electrostatic precipitation method was used for the determination of 222Rn gas concentration. The mean activity concentration of 222Rn gas (Co) was found to be 123 +/- 22 Bq m(-3). A mean unattached fraction (fp) of 0.11 +/- 0.02 was obtained at a mean aerosol particle concentration (Z) of (3.0 +/- 0.21) x 10(3) cm(-3). The mean equilibrium factor (F) was determined to be 0.35 +/- 0.03. The mean PAEC was found to be 37 +/- 8.1 Bq m(-3). The activity size distribution of (214)Pb shows mean activity median diameter of 290 nm with mean geometric standard deviation (sigma) of 2.45. At a total deposition fraction of approximately 23% the total effective dose to the lung was determined to be approximately 1.2 mSv. The second part of this paper deals with a study of natural radionuclide contents of samples collected from the building materials of those rooms under investigation given in part one of this paper. Analyses were performed in Marinelli beakers with a gamma multichannel analyser provided with a NaI(Tl) detector. The samples have revealed the presence of the uranium-radium and thorium radioisotopes as well as (40)K. Nine gamma-lines of the natural radioisotopes that correspond to 212Pb, 214Pb, 214Bi, 228Ac, 40K and 208Tl were detected and measured. The activity concentrations of 226Ra, 232Th and 40K were determined with mean specific activities of 65 +/- 22, 35 +/- 12 and 150 +/- 60 Bq kg(-1), respectively. These activities amount to a radium equivalent (Ra(eq)) of 126 Bq kg(-1) and to a mean value of external hazard index of 0.34.     

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).     

Radon in workplaces: first results of an extensive survey and comparison with radon in homes

Extensive radon surveys have been carried out in many countries only in dwellings, whereas surveys in workplaces are rather sparse and generally restricted to specific workplaces/activities, e.g. schools, spas and caves. Moreover, radon-prone areas are generally defined on the basis of radon surveys in dwellings, while radon regulations use this concept to introduce specific requirements in workplaces in such areas. This approach does not take into account that work activities and workplace characteristics can significantly affect radon concentration. Therefore, an extensive survey on radon in different workplaces have been carried out in a large region of Italy (Tuscany), in order to evaluate radon distribution in workplaces over the whole territory and to identify activities and workplace characteristics affecting radon concentration. The results of this extensive survey are compared with the results of the survey carried out in dwellings in the same period. The workplaces monitored were randomly selected among the main work activities in the region, including both public and industrial buildings. The survey monitored over 3500 rooms in more than 1200 buildings for two consecutive periods of ～6 months. Radon concentration was measured by means of passive nuclear track detectors.     

Deposition and clearance for radon progeny in the human respiratory tract

In vivo counting of 214Pb was conducted to estimate the deposition and retention of radon progeny in the human respiratory tract. Two volunteer subjects were exposed to high radon concentrations. After the exposures, activity deposited in the extrathoracic (ET) region for each subject was measured using a NaI(Tl) detector. According to the International Commission on Radiological Protection (ICRP) model, a reference value for particle transport rate from ET2 to the GI tract is 100 d(-1) (half-time, 10 min). The effective half-time of 214Pb deposited in the ET region was calculated for pure nose and mouth breathers, using the ICRP reference transport rate. While the measured half-times for nose breathers were generally consistent with the calculated values, those for mouth breathers were significantly larger than the calculated values. The results indicated that the particle transport rate from ET2 to the GI tract was much smaller than the reference value in the ICRP model.     

Microwave plasma enhanced chemical vapor deposition diamond synthesis from high carbon content source

To synthesize diamond films by microwave plasma enhanced chemical vapor deposition (MPECVD), the methane concentration (CH₄/H₂)plays a crucial role. It is well-known that there always exists a critical methane concentration (≤0.6%) only below which a good quality diamond film can be obtained. In this study, however, the phenomena of diamond synthesis resulting from high carbon concentration conditions were observed. The molten metals, e.g., Ag, Cu, were used as the deposition substrates on which crystalline diamonds can be achieved from a methane content of CH₄/H₂≥6% or even from solid carbon sources. These results suggest that there may exist a low methane content boundary layer (<0.6%) in the proximity of molten metal surface on which suitable species, CH, CH⁺, H_α and H_β are composed for the diamond nucleation and growth similar to the condition as in the conventional low methane contents. The molten metal inclines to dissolve other forms of carbonaceous materials other than diamond, and thus keeps a much higher steady supply of carbon atoms that enhances the quality as well as the growth rate of the forming diamonds. Received: 23 June 2001 / Accepted: 23 July 2001     

Multimodal ultrafine grain size distributions from severe plastic deformation at high strain rates

Severe plastic deformation at high strain rates in machining is explored as a vehicle for engineering grain size distributions in copper. Typical strengthening in unimodal, ultrafine grained chips is found to accompany poor ductility when generated at large strains but low strain rates. However, at higher rates, in situ heating in the deformation zone engenders dynamic recovery that results in material with a multimodal grain size distribution that is comparable in strength to the unimodal chips, but additionally possesses improved ductility.     

Recent developments in radon metrology: new aspects in the calibration of radon, thoron and progeny devices

Due to the importance of reliable measurements of radon activity concentration, one of the past developments in metrology was applied to the field of radon, thus meeting two basic needs: (1) the harmonisation of metrology within the scope of the mutual recognition arrangement, an arrangement drawn up by the International Committee of Weights and Measures for the mutual recognition of national standards and of calibrations issued by national metrology institutes and (2) the increased demands of the European Atomic Energy Community (EURATOM) directive, transferred into national radiation protection regulations with regard to natural radioactivity and its quality-assured measurements. This paper gives an overview of typical technical procedures in the radon-measuring technique group of PTB, covering all aspects of reference atmospheres (primary standards) for radon, thoron and their respective progenies.     

Internal microdosimetry of inhaled radon progeny in bronchial airways: advantages and limitations

The objective of the present study was to identify advantages and limitations of the application of microdosimetric concepts for inhaled radon progeny activities in the lungs. The methods employed for this analysis were a recently developed Monte-Carlo microdosimetry code for the calculation of energy deposition in bronchial target cells and the Probability Per Unit Track Length (PPUTL) model, which relates these microdosimetric parameters to cellular radiation effects. The major advantages of internal microdosimetry of radon progeny in bronchial airways are: (i) quantitative characterisation of non-uniform dose distributions and identification of target sites with enhanced carcinogenic potential, (ii) quantification of low doses of alpha particles by the number of cells hit and the dose received by those cells, (iii) illustration of the random variations of cellular doses by specific energy distributions and (iv) establishment of a direct link to cellular radiobiological effects. At present, a major limitation of microdosimetry is the extrapolation of the response of individual cells to the resulting tissue response, which is still not fully explored.     

QA programme for radon and its short-lived progeny measuring instruments in NRPI Prague

To subserve the institutional research and tasks coming out from the Czech National Radon Programme, a new QA programme to calibrate all the known types of devices that measure radon and its short-lived progeny was developed at the Department of Radon mobile group of the National Radiation Protection Institute (NRPI) at Prague. The programme also included calibration of instruments measuring a unique quantity of unattached and attached fractions of short- lived radon progeny Generally, NRPI declares estimation of radon concentration during all routine calibration measurements with an overall uncertainty <5% (one sigma) and of equilibrium-equivalent radon concentration with an overall uncertainty <10% (one sigma). The results of the comparative measurements of the unattached and attached fractions of each short-lived radon progeny carried out with a comparing continuous monitor Fritra 4 in the German reference radon chamber at PTB Braunschweig indicated an acceptable level of agreement, up to 10%.     

Radon progeny microdosimetry in human and rat bronchial airways: the effect of crossfire from the alveolar region

The objectives of the present study were (1) to present a comprehensiveanalysis of the microdosimetric quantities in both human andrat bronchial airways and (2) to assess the contribution ofthe crossfire alpha particles emitted from the alveolar regionto bronchial absorbed doses. Hit frequencies, absorbed dosesand critical microdosimetric quantities were calculated forbasal and secretory cell nuclei located at different depthsin epithelial tissue for each bronchial airway generation fordefined exposure conditions. Total absorbed doses and hit frequencieswere slightly higher in rat airways than in corresponding humanairways. This confirms the a priori assumption in rat inhalationexperiments that the rat lung is a suitable surrogate for thehuman lung. While the contribution of crossfire alpha particlesis insignificant in the human lung, it can reach 33% in peripheralbronchiolar airways of the rat lung. The latter contributionmay even further increase with increasing alveolar ²¹⁴Po activities.Hence, the observed prevalence of tumors in the bronchiolarregion of the rat lung may partly be attributed to the high-linearenergy transfer crossfire alpha particles.     

Strength distributions and size effects for 2D and 3D composites with Weibull fibers in an elastic matrix

Monte Carlo simulation and theoretical modeling are used to study the statistical failure modes in unidirectional composites consisting of elastic fibers in an elastic matrix. Both linear and hexagonal fiber arrays are considered, forming 2D and 3D composites, respectively. Failure is idealized using the chain-of-bundles model in terms of -bundles of length , which is the length-scale of fiber load transfer. Within each -bundle, fiber load redistribution is determined by local load-sharing models that approximate the in-plane fiber load redistribution from planar break clusters, as predicted from 2D and 3D shear-lag models. As a result the -bundle failure models are 1D and 2D, respectively. Fiber elements have random strengths following either a Weibull or a power-law distribution with shape and scale parameters and , respectively. Under Weibull fiber strength, failure simulations for 2D -bundles, reveal two regimes: When fiber strength variability is low (roughly >2) the dominant failure mode is by growing clusters of fiber breaks, one of which becomes catastrophic. When this variability is high (roughly 0<<2) cluster formation is suppressed by a dispersed failure mode due to the blocking effects of a few strong fibers. For 1D -bundles or for 2D -bundles under power-law fiber strength, the transitional value of drops to 1 or lower, and overall, it may slowly decrease with increasing bundle size. For the two regimes, closed-form approximations to the distribution of -bundle strength are developed under the local load-sharing model and an equal load-sharing model of Daniels, respectively. The results compare favorably with simulations on -bundles with up to 1500 fibers.     

Radon in soil gas--investigation and data standardisation at radon reference sites, Czech Republic

Radon risk mapping at building sites in the Czech Republic indicate an advisable level of protection of buildings against the penetration of radon from the geological basement. Various techniques and instruments are used for the measurement of radon in soil gas. A national radon chamber and three radon reference sites in Central Bohemia enable radon data standardisation. Tests of field radon measurements and the reported radon activity concentration in soil gas at the reference sites are based on comparisons with other organisations and with a database of reference site measurements. The radon reference sites have been used for various investigations of radon in soil gas during the period 2000-07.     

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.     

Application of a mid-infrared fiber bundle in remote measurement of gas concentrations in a chemical vapor deposition chamber

A fiber bundle has been designed for measurement of gas concentrations in a chemical vapor deposition (CVD) chamber. The bundle is broadband, covering the spectrum range from 500 to 6000 cm(-1). Using this bundle, we have designed Fourier Transform infrared (FTIR) sampling configurations with reduced beam divergence (from 0.4 to 0.1 rad) and focal spot diameters (from 12 to 4 mm). The FTIR spectrum of tetraethoxysilane vapors in a CVD chamber was determined with the bundle and modified SAM connectors. An ellipsoid reflector was designed that yielded improved signal-to-noise ratios (SNR's) in the fiber-based spectra by a factor of 2. The incorporation of this reflector in spectrometers by use of the fiber bundle has the potential to reduce the sampling times for spectra while retaining acceptable SNR's.     

Grain-to-grain variations in NbC particle size distributions in an austenitic stainless steel

Quantitative information has been obtained concerning the size distributions of NbC precipitate particles in different grains in a deformed and aged austenitic stainless steel specimen. The precipitate size distributions obtained differ from one grain to another. The average disparity measured between the mean precipitate sizes was a function of the distance betwen the grains compared. The results obtained are considered in terms of differences in precipitation behaviour due to variations in the levels of plastic strain in constituent grains of the deformed specimen.Formerly Department of Pure Mathematics and Mathematical Statistics, University of Cambridge     

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.     

中型氡室温湿度智能控制系统设计

氡室可以对广泛使用的各种测氡仪器进行刻度、性能测试,并进行氡的控制实验。国家有关标准规定,氡室的温度应该在-5℃到＋40℃内可控,在测氡仪的标定过程中应使用常温标定,并且湿度要满足一定的要求。依照校准规定,本文研究设计了一种中小型氡室温湿度智能控制系统方案,详细阐述了AVR单片机与温湿度传感器、氡室制冷系统和除湿系统等部件接口实现的软、硬件技术要点。通过理论计算对设计方案进行分析,结果表明是可行的。控制系统既可以独立完成对氡室温湿度的监控,也可以通过RS-232C接口与PC机通信,组成基于PC机的集成控制系统。