Progeny In Air Research Articles

Comparative studies on radon seasonal variations in various undeground environments: Cases of abandoned Beshtaugorskiy uranium mine and Kungur Ice Cave

It is well known that one of the most important risk factors in underground environment is the harmful effects of radon. The reasons for strong seasonal fluctuations in radon content in underground environments remain not fully understood. The purpose of this article is to improve existing ideas about this phenomenon. The article presents the results of a study of radon transport in two different underground spaces – the Beshtaugorskiy uranium mine (North Caucasus) and the Kungur Ice Cave (Middle Ural). We have used the direct measurements of the equilibrium equivalent concentration (EEC) of radon progeny in air, as well as the air flow velocity. A very wide range and strong seasonal variations in the radon levels have been recorded in both cases. The EEC has a range of 11–6653 by Bq m−3 and 10–89,020 Bq m−3 in the Kungur cave and the Beshtaugorskiy mine, respectively. It has been established that seasonal fluctuations in radon levels both in the mine and in the cave are caused by the same process – convective air circulation in the underground space due to the temperature difference between the mountain massif and the atmosphere (so called chimney effect). Overall, these results indicate that due to convective air circulation, underground spaces are periodically intensively ventilated with atmospheric air, and then, on the contrary, they are filled with radon-enriched air that seeps into caves or adits from rocks and ores. In both cases, the EEC of radon progeny exceeds the permissible level for the population and workers. The results of this study highlight the need for the development of measures to limit the presence of people in the surveyed underground spaces.

Dosimetry of radon progeny deposited on skin in air and thermal water.

It is held that the skin dose from radon progeny is not negligibly small and that introducing cancer is a possible consequence under normal circumstances as there are a number of uncertainties in terms of related parameters such as activity concentrations in air and water, target cells in skin, skin covering materials, and deposition velocities. An interesting proposal has emerged in that skin exposure to natural radon-rich thermal water as part of balneotherapy can produce an immune response to induce beneficial health effects. The goal of this study was to obtain generic dose coefficients with a focus on the radon progeny deposited on the skin in air or water in relation to risk or treatment assessments. We thus first estimated the skin deposition velocities of radon progeny in air and thermal water based on data from the latest human studies. Skin dosimetry was then performed under different assumptions regarding alpha-emitting source position and target cell (i.e. basal cells or Langerhans cells). Furthermore, the impact of the radon progeny deposition on effective doses from all exposure pathways relating to ‘radon exposure’ was assessed using various possible scenarios. It was found that in both exposure media, effective doses from radon progeny inhalation are one to four orders of magnitude higher than those from the other pathways. In addition, absorbed doses on the skin can be the highest among all pathways when the radon activity concentrations in water are two or more orders of magnitude higher than those in air.

Monitoring of the unattached fraction of radon progeny by the Kodak LR-115 Type 2, nuclear track detector

The experimental Unattached Radon Progeny Fraction Monitor (URPFM) was developed for the parallel monitoring of all radon progeny and the fraction of radon progeny in air that is attached onto aerosols. The optimum monitor arrangement includes two radon progeny sampling columns with each column incorporating a 0.8μm membrane filter. The filter in the first sampling column collects all the ambient radon progeny that are measured by the Kodak LR-115 nuclear track detector. The second sampling column also includes a fine mesh that removes the unattached radon progeny from the sampled air and thus the track detector that is situated above the mesh measures the unattached radon progeny.Three, five to thirteen-day long radon progeny monitoring periods were conducted inside a sealed room of a residential house and outdoors at an open cut uranium mine. The average unattached fraction of radon progeny was measured to be between 0.09 and 0.14 for the residential house, and between 0.08 and 0.10 for the open cut uranium mine.

Radon and Progeny Detection Using Tensioned Metastable Fluid Detectors.

Radon and other alpha-emitting nuclides in air can be a significant risk for health hazards in the workplace and in dwellings. Radon gas in US homes causes over 21,000 deaths from lung cancer annually, according to the US Environmental Protection Agency (US EPA). Alpha-emitting radionuclides from airborne contamination in the nuclear industry also constitute a known safety and security-safeguards related issue. Purdue University, along with Sagamore Adams Laboratories LLC, have developed the tensioned metastable fluid detector (TMFD) sensor technology for general-purpose alpha-neutron-fission. For radon detection, radon gas in air is sparged through the TMFD detection fluid, after which this radon-bearing fluid is placed into a tensioned metastable state. In this metastable state, an audible-visible cavitation (alpha radiation) detection event is created and electronically recorded. Tailoring the level of tension enables spectroscopic information through energy discrimination of radon and its progeny; This is also applicable to other alpha emitting isotopes (Pu, Cm, U…). TMFDs boast high intrinsic detection efficiencies (>95%) for alpha spectroscopy while remaining blind to background beta and gamma radiation even in ~10 R h fields. The immunity to beta and gammas allows for reusability of the detection fluid through immunity to beta buildup from thoron and radon progeny. TMFD technology was used to measure the concentration of radon and radon progeny in air for concentrations from 74 Bq m to 740 Bq m. The system measures radon concentration between these levels within 24 h with an intrinsic relative error (IRE) of ± 15% according to the standards set forth by the American Association of Radon Scientists and Technicians-National Radon Proficiency Program (AARST-NRPP) Device Evaluation Program (DEP). Precision evaluation defined using the relative standard deviation set by the AARST-NRPP measured a deviation of <5%, which exceeds the requirement of <25%. Temperature effects from 10°C and 27°C were assessed and corrected for dynamically. A radon decay correction method was introduced to correct for the radon activity decrease in the detection fluid over the counting period due to the ~3.8 d half-life. Blind testing was also successfully performed* with standards from the ; within 6 h, the TMFD-based technology accurately measured the concentration of radon to within 20% of the reference standards. Non-condensing relative humidity levels up to 95% per AARST-NRPP were assessed for and were found to have no impact on radon detection. This work improves upon the previous work by splitting the calibration curve into two distinct regions and adds additional information pertaining to the effects of relative humidity on the system.

INFLUENCE OF RADON PROGENY ON DOSE RATE MEASUREMENTS STUDIED AT PTB'S RADON REFERENCE CHAMBER.

The responses of electronic dose rate meters were investigated in a large volume radon chamber at PTB in a wide range of radon activity concentrations. The measurements were conducted under controlled laboratory conditions and measured dose rate data are compared with Monte-Carlo simulations. Consequences concerning environmental monitoring are described. A further result is that the direct measurement of the dose rates produced by radon progeny in air is hardly possible in radon atmospheres with high activity concentrations, because the major contribution of measured dose rates is produced by radon progeny on the housing of the dose rate instruments. The latter effect largely depends on the ability of surfaces to absorb radon progeny. The Monte-Carlo simulations revealed quantitative results on the height of the single contributions to the total dose rate measured in the radon chamber. When environmental dose rate measurements are performed, the plate-out on detectors can be neglected.

Measurements of the size distribution of unattached radon progeny by using the imaging plate

The size distribution of unattached radon progeny is an important parameter for an accurate estimation of the internal dose of radon exposure. In this study, a new measuring system was developed to evaluate the size distribution of unattached radon progeny in air. In the system, airborne radon progeny were collected with a newly designed graded screen array (GSA), the activity concentrations were measured by using the imaging plate technique, and the size distribution of unattached fraction was retrieved by using an iterative nonlinear algorithm. The simulation results indicated that the collection characteristics of the new GSA system were well agreed with other systems. Test experiments showed that the activity-weighted median diameters (AMD) for unattached 218Po, 214Pb and 214Bi were 0.89 ± 0.11 nm, 0.96 ± 0.13 nm and 1.01 ± 0.25 nm in a particle-free radon chamber, and the distribution changed with different concentrations of particles. As multiple measurements can be simultaneously carried out with a single IP, the new technique is considered as an optional and useful way to measure the size distribution measurement of unattached radon progeny.

Studying the response of CR-39 to radon in non-polar liquids above water by Monte Carlo simulation and measurement

The application of CR-39 has been extensive for measurement of radon and progeny in air of dwellings, but limited as regards to measurements of radon in water. In this paper, a new method is introduced for efficient measurement of radon in water by registering alpha particle tracks in a CR-39 detector placed in a non-polar medium such as cyclohexane, hexane and olive oil when each mixed with water, then separated and fixed above water, as a two-phase media. The method introduced here is however different from the widely used liquid - liquid extraction technique by liquid scintillation spectrometry since it is a passive detection method (CR-39) in a non-polar liquid with enhanced absorption of radon in the liquid, it has a capability for long sample counting to decrease the minimum detection limit (MDL), it does not require sophisticated low light counting systems, and it has the potential for simultaneous measurements of large number of samples for large-scale applications. It also has a low cost and is readily available. A new Monte Carlo calculation of energy-distance travelled by alphas from radon and progeny in a medium was also investigated. The sensitivity of CR-39 detector to radon and progeny in water was determined under two conditions; in a single-phase and two-phase media. In a single-phase medium, CR-39 is directly placed either in air, water, cyclohexane, hexane or olive oil. When CR-39 is placed directly in water, its sensitivity is (2.4 ± 0.1) × 10 −4 (track/cm 2 )/(Bq.d/m 3 ). In the two-phase media, CR-39 is placed either in cyclohexane, hexane or olive oil when each is fixed above water. The sensitivities in the two-phase media are significantly enhanced and are respectively (1.98 ± 0.10) × 10 −2 , (2.8 ± 0.15) × 10 −2 and (2.86 ± 0.15) × 10 −2 (track/cm 2 )/(Bq.d/m 3 ). The sensitivies are about 76, 82 and 110 times more than that of when CR-39 is directly placed in water. The new method is a novel alternative for radon measurements in water with a lower MDL than that of for example liquid scintillation method with a number of advantages. The results are presented and discussed. ► A new passive detection method is introduced for efficient radon measurements in water. ► Method is based on alpha tracks of radon/progeny in CR-39 in a non-polar medium above water. ► Sensitivity was enhanced (>80 times) relative to water by radon/progeny detected in hexane. ► Monte Carlo simulation was applied to determine CR-39 sensitivity to radon/progeny in water. ► The method has a number of advantages with MDL lower than alternative wide-scale methods.

Measuring radon progeny and thoron progeny in air by absolute beta counting subsequent to grab sampling

A new grab sampling method for the simultaneous determination of radon progeny and thoron progeny in air has been developed and demonstrated by the first author of this paper a few years ago. The characteristics and capabilities of this method are discussed in the present paper in detail. The method is based on gross beta counting of filtered aerosol samples counted over successive time intervals using an end-window Geiger–Müller counter. The measured counting rate versus time curve is analyzed by fitting to it some linear combination of the theoretical decay curves of the decay products with the knowledge of the counting efficiencies and some other quantities. Defined solid angle absolute beta counting was used to evaluate the counting efficiencies for the decay products one by one. So, the method is an absolute one that does not demand further calibration. The decay products of radon and thoron can be determined separately and simultaneously. The systematic error of the results, deriving from the inaccurate evaluation of the counting efficiencies, is probably lower and can be estimated more surely than that of the methods based on alpha counting. The method is highly sensitive: accurate results can be obtained for 214Pb, 214Bi, 212Pb, EEDC 222 and EEDC 220 even outdoors. However, the results for 218Po and 212Bi are much more inaccurate and 208Tl cannot be determined at all. The reliability of the determinations can be raised significantly using conditional computations based on the information obtainable from some theoretical considerations and models. The method can be used in a broad activity concentration range, equally in caves, mines, houses or outdoors. The above characteristics and capabilities of the method are demonstrated in this paper through the detailed presentation and analysis of the results obtained for three samplings performed indoors in a house, in a cave, and outdoors, respectively. The known advantages and drawbacks of the method are also surveyed in detail.

Using an Imaging Plate to Measure the Concentration of Radon Progeny in Air

A simple technique was developed for using an imaging plate (IP) to estimate the individual concentrations of radon progeny in the air. The objective of this technique is to survey concentrations in high-humidity environments, such as caves, utility mains, and underground facilities.An IP called BAS-III, which performs well in extremely humid environments, was selected. The sampling flow rate was 65 liters per minute by a 47 mm-dia. glass-fiber filter (GF/F), and the grab sampling time was determined to be 5-10 minutes. One minute after the air sampling, the surface of the filter was attached directly to the IP in a prepared cassette. This was repeated six times for 10 minutes, for a total exposure of 60 minutes. Six values of Photo-Stimulated Luminescence (PSL) indicating the decay curve of the radon progeny sampled on the filter were analyzed. In environments with extremely high concentrations of radon, more accurate measurements can be obtained by making a simple distinction between PSL values for α and β rays. The lower detection limit for the equilibrium equivalent concentration (EEC) of radon was estimated to be about 20 Bqm-3. This system can be successfully adopted in humid areas.

A quick method for estimation of long-lived alpha activity in work atmospheres.

In an operating plant quick reporting of the status of long-lived alpha activity concentrations in the work atmosphere is required. This will help in taking any corrective control measures if required. Radon and thoron progeny concentrations prevalent in the general atmosphere predominantly interfere in measurement of long-lived alpha activity in air. The alpha counts due to radon and thoron progeny vary widely in many atmospheric conditions. Therefore, conventionally, 5 days delay is allowed for all interfering activity to decay completely and true alpha air activity is then estimated. An approach for quick assessment of long-lived alpha activity by eliminating interference due to radon and thoron progeny in air, is made here. Based on the study of the pattern of alpha count rate due to radon and thoron progeny in air, a method for estimation of long-lived alpha activity within 8 hours delay time is suggested in this paper.

Testing Extrapolation of a Biologically Based Exposure–Response Model from in Vitro to in Vivo Conditions

Models of carcinogenesis may become so flexible as to preclude the possibility of being falsified by data. This problem is removed in part by stronger biophysical specification of processes and parameters within the model prior to fitting to in vivo data on the relationship between exposure and cancer incidence. This paper explores the use of a biophysical model of chromosomal damage, cellular transformation, repair, mitosis, initiation, promotion, progression, and cytotoxicity in developing exposure–response models for radiation-induced cancer. Many of the aspects of model form and parameter values are developed from in vitro data, and the model then is extrapolated to the in vivo setting using a dosimetric model to account for dose inhomogeneity within the lung tissue of rats exposed to radon progeny in air. The ability of the model to predict cancer incidence in the rats is assessed and is shown to be problematic at higher doses. This calls into question whether a full claim may be made about the ability of first-principle models to fully constrain models applied to in vivo data at present. Possible explanations for the discrepancy, and implications for extrapolation, are provided.

Intermittent Measurements of 222Rn and 220Rn Progeny in Air for Four Years.

To survey the level and behavior of 222Rn and 220Rn progeny in air, measurements were made intermittently (once a day at an identical time) for 4 years at the campus of the authors' college located in the northeastern part of Japan. A filtration method with alpha spectroscopy, using an evacuated chamber, clearly separated 212Po peak from others. Outdoor and indoor air were sampled every morning except holidays. A definite seasonal variation, higher concentrations in autumn and in winter, was observed except indoor 220Rn progeny. 222Rn progeny revealed log-normal distribution, whereas 220Rn progeny revealed Poisson-like distribution. Multiple regression analysis and correlation analysis indicated that most of indoor 222Rn progeny originates from outdoor air. From time series analysis, several-day periods were often observed, which will probably be attributed to the wind speed.

Radon, radon progeny and equilibrium factor determination using an LR115 detector

Sensitivity, of an open LR115 type II strippable detector for radon and its progeny determination, depends on the layer removed by etching and this is theoretically studied in this paper. Based on the results obtained by this study, three new approaches to the long term measurement of alpha emitting radon progeny in air are proposed. Track density on an open LR115 track detector grows with increasing removed layer (or with etching time). This growth is dependent on the equilibrium factor between radon and its short lived progeny. The first method, which determines the equilibrium factor, is based on this fact, and assumes multi step etching of the detector. The second method determines the concentration of 214Po in air. The method is based on the different behaviour of 222Rn, 218Po and 214Po partial sensitivities with increasing removed layer. The third method called the “obstacle” method enables the determination of 218Po and 214Po in air. This method requires an obstacle in front of an open LR115 detector. The partial sensitivities of 222Rn, 218Po and 214Po in such obstacle exposure geometry, behave differently to allow their determination. A similar method can be developed for other SSNTD possessing an upper energy limit for alpha detection.

Aa Automated Gross Alpha/Beta Activity Monitor Applied to Time-resolved Quantitative Measurements of 222Rn Progeny in Air

Automated monitors for the determination of airborne radioactivity are widely in use as early warning systems for nuclear emergencies; however, the data acquired for this purpose are seldom used for analyzing spatial and temporal variations of natural radioactivity (especially radon and short-lived decay products). This paper shows that a specific type of airborne gross alpha/beta activity monitor, applied in several European emergency networks, can be effectively used to study the transport of 222Rn progeny in the outdoor environment. Real-time recordings (10-min sampling time) can, independent of the actual equilibrium ratio, be converted to the equilibrium-equivalent decay-product concentration (EEDC) of 222Rn. Medium volume air sampling and a slow-moving tape air sampler yield a low detection limit of < or = 0.1 Bq m-3. This paper further describes all factors and processes contributing to the uncertainty in the data obtained in this way; the total error in single recordings is estimated at 20-25% (95% confidence interval). Data of 222Rn progeny obtained from the Dutch National Radioactivity Monitoring network agree with results of other radon surveys.

Ventilation Rates by Measurement of Induced Radon Time-Dependent Behavior—Theory, Application, and Evaluation

The use of induced time-dependent 222Rn behavior to determine source rate magnitudes, ventilation rates (air change rates), and other parameters that affect 222Rn and progeny levels and exposure to building occupants is investigated. When the subject space is purged and the buildup (seepage) back into the space is measured, theoretical, normalized equations show a unique, one-to-one correspondence of the 222Rn and particulate progeny temporal levels to the air change rate in the space. The Bateman equations have been solved in closed form for 222Rn and progeny in air and trapped on a filter under these conditions. A total of 28 measurements of the time-dependent behavior of radon progeny for two test facilities [one with a constant air change rate and one with a constant National Institute of Standards and Technology (NIST)-calibrated source] and four residential dwellings were made. The results were compared with theory and with air change rate measurements made by anemometer flow rates and by the conventional method (SF6 decay). For a factor of 2 range in air change rates in the NIST constant source case, the agreement with the SF6 method air change rate was within ±10.6% standard deviation and agreement with the NIST source magnitude of 37.0 ± 1 kBq was within ±4.9% standard deviation. Agreement to within ±17.7% standard deviation was obtained on determination of air change rates for the residential dwellings. Based on the airborne concentrations and air change rates, source emanation rate magnitudes were obtained. Analyses of the results are presented in detail, and factors affecting the accuracy and feasibility of the method are identified.

Theoretical Response of a ZnS (Ag) Scintillation Detector to Alpha-emitting Sources and Suggested Applications

The classic problem of alpha absorption is discussed in terms of the quantitative determination of the activity of "weightless" alpha sources and the specific alpha activity of extended sources accounting for absorption in the source medium and the window of a large area ZnS(Ag) scintillation detector. The relationship for the expected counting rate gamma of a monoenergetic source of active area A, specific alpha activity C, and thickness H that exceeds the effective mass density range Rs of the alpha particle in the source medium can be expressed by a quadratic equation in the window thickness x when this source is placed in direct contact with the window of the ZnS(Ag) detector. This expression also gives the expected counting rate of a finite detector of sensitive area A exposed to an infinite homogeneous source medium. Counting rates y obtained for a source separated from a ZnS(Ag) detector by different thicknesses x of window material can be used to estimate parameter values in the quadratic equation, y = a + bx + cx2. The experimental value determined for the coefficient b provides a direct estimation of the specific activity C. This coefficient, which depends on the ratio of the ranges in the source medium and detector window and not the ranges themselves, is essentially independent of the energy of the alpha particle. Although certain experimental precautions must be taken, this method for estimating the specific activity C is essentially an absolute method that does not require the use of standards, special calibrations, or complicated radiochemical procedures. Applications include the quantitative determination of Rn and progeny in air, water, and charcoal, and the measurement of the alpha activity in soil and on air filter samples.