Short-lived Radon Decay Products Research Articles

Long-Term Measurements of Equilibrium Factor and Unattached Fraction of Short-Lived Radon Decay Products in a Dwelling - Comparison with Praddo Model

According to the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR 1993), the dose due to the inhalation of radon decay products represents almost 50% of the total natural radiation dose to the general population. The scientific community is interested in the assessment of the risk induced by domestic radon exposure. The dosimetric models used to estimate the dose are very sensitive to unattached fraction and size distributions, which makes the characterization of the indoor radon decay products aerosol necessary. For this purpose, longterm measurements of unattached fraction (fp ) and equilibrium factor (F) were taken in a dwelling under typical indoor domestic aerosol conditions. An original device consisting of an annular diffusion channel set in parallel with an open filter was developed and calibrated to continuously measure the unattached fraction. Moreover, radon activity concentration and particle concentration were simultaneously monitored. With aged aerosol, particle concentration was found to be very low (between 500 and 5000 cm-3), radon activity concentration ranged from 240 to 2800 Bq m-3, and the mean values of fp and F were, respectively, 0.31 (0.08-0.67) and 0.16 (0.04-0.45). With aerosol sources, the high increase in particle concentration led to a negligible unattached fraction and raised the equilibrium factor. A correlation relationship was determined between these two parameters under different aerosol conditions. Finally,our experimental results were compared to results obtained with the PRADDO model; this comparison showed a good agreement between these two different approaches.

Diurnal and seasonal variation of the equilibrium state between short-lived radon decay products and radon gas in ground-level air.

To study seasonal and diurnal variations and the effect of meteorological parameters, the equilibrium factor F (i.e. the ratio of equilibrium equivalent radon daughter concentration and radon gas concentration) was determined as a result of measurements on a test field at Munich-Neuherberg, Germany, continuously from October 1995 through March 1997. On average, F was found to be 0.62+/-0.09 (95% confidence level). The time series of F showed no distinct seasonal variations. Nevertheless, typical diurnal variations as well as seasonal variations of the diurnal behaviour were observed. Generally, F was found to be increased in the early afternoon, i.e. under conditions of enhanced vertical mixing in the atmosphere. The daily differences between high and low values of F depended on the season. On average, low F values were characteristic for days with precipitation and high wind speed, i.e. under turbulent atmospheric conditions. Therefore, taking daily mean values into account, F was found to be positively correlated with the aerosol concentration, although a relationship between the diurnal behaviour of the aerosol concentration and that of F was not detectable.

Physical parameters and dose factors of the radon and thoron decay products.

The dose per exposure unit of the short-lived radon and thoron decay products was calculated using a dosimetric approach. The calculations are based on a lung dose model with the structure that is related to the ICRP 66 respiratory tract model. The dose relevant parameters, unattached fraction of the decay product clusters (fp) and size distribution of the unattached and aerosol-attached decay products for different living and working places are reported. Taking into account these characteristics the dose conversion factors (DCF) of the radon and thoron decay products were estimated. In addition, the living and working places were divided concerning their aerosol parameters like particle number concentration and activity size distribution.

Determination of neutralisation rates of 218Po ions in air.

The electric charge of the radon decay product, 218Po, has an influence on its mobility characterised by the diffusion coefficient, which chiefly controls the formation of the radioactive aerosol by attachment and the plateout processes on surfaces. These processes strongly affect the dose relevant quantities like concentration and particle size distribution of the short-lived radon decay products. The neutralisation rate of the positive 218Po ions in environmental air was determined quantitatively in chamber experiments. The experimental results show the great influence of the ionisation rate and the humidity concentration on the neutralisation rate of the 218Po ions in air. The obtained neutralisation rates were described by equations, taking into account the neutralisation processes like ion recombination, charge transfer and electron scavenging. In 'normal' environmental air with an ionisation rate of 45 muR.h(-1) = 1.16 x 10(-8) C/(kg.h) and a relative humidity of 50% (T = 20 degrees C), a neutralisation rate of the 218Po ions of 1.54 x 10(-2) s(-1) was obtained. Taking into account this neutralisation rate leads to a fraction of about 51% of the Po cluster that are neutral in air.

Long-Term Measurements of Equilibrium Factor and Unattached Fraction of Short-Lived Radon Decay Products in a Dwelling - Comparison with Praddo Model

According to the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR 1993), the dose due to the inhalation of radon decay products represents almost 50% of the total natural radiation dose to the general population. The scientific community is interested in the assessment of the risk induced by domestic radon exposure. The dosimetric models used to estimate the dose are very sensitive to unattached fraction and size distributions, which makes the characterization of the indoor radon decay products aerosol necessary. For this purpose, longterm measurements of unattached fraction (fp ) and equilibrium factor (F) were taken in a dwelling under typical indoor domestic aerosol conditions. An original device consisting of an annular diffusion channel set in parallel with an open filter was developed and calibrated to continuously measure the unattached fraction. Moreover, radon activity concentration and particle concentration were simultaneously monitored. With aged aerosol, particl...

Aerosol size distribution of the radon progeny in outdoor air

The activity size distribution of the short-lived radon decay products in ambient air was measured continuously over several weeks. Two different measurement techniques were used: A direct measurement with a low-pressure on-line alpha cascade impactor (OLACI) and an indirect determination based on measurement with a differential mobility analyser (5–200 nm) and a laser aerosol spectrometer (100–5000 nm). In parallel, the meteorological parameters like temperature, rainfall intensity and wind velocity were registered. The measured activity size distribution of the radon progeny can be approximated by a sum of three log-normal distributions. The greatest activity fraction was adsorbed on aerosol particles in the accumulation size range (100–1000 nm) with activity median diameters (AMD a) and geometric standard deviations ( σ ga) values of 250–450 nm, and 1.5–3.0, respectively. The influence of the weather conditions on the activity of the accumulation particles was not significant. In contrast to the results of measurements in houses, a small but significant fraction of the radon progeny (average value: 2%) was attached to coarse particles (>1000 nm). This fraction varied between 0 and 10%. The direct measurements with the OLACI yielded a higher activity fraction (20–40%) in the nucleation size range (<100 nm) compared to the values evaluated from the number size distribution measurement (indirect measurement). This fraction depends on the number concentration of the atmospheric aerosol in this size range. A diurnal variation of the particle number concentration and of the activity fraction for the nucleation particles was found. In the case of lower particle concentrations (diameters <50 nm) in air during the night no nucleation mode was registered using the indirect measurement technique.

Chromosomal aberrations of blood lymphocytes induced in vitro by radon-222 daughter α-irradiation

Blood samples were irradiated in vitro with α-rays emitted from short-lived radon decay products dissolved in the culture medium at doses between 0.03 and 41.4 mGy. The data were collected from experiments conducted during the period 1984–1992 and comprise a total of about 64000 scored metaphases. For statistical reasons, only 60,022 metaphases were used for the subsequent analysis. The results for total chromosome aberrations and dicentrics indicate a linear dose dependence in the dose range above about 10 mGy, consistent with other experimental observations. At doses below about 10 mGy, aberration frequencies cannot be linearly extrapolated from higher doses, suggesting that there is no dependence on dose within a certain low-dose range. In addition, a statistically significant minimum has been observed at a dose of about 0.03 mGy, which is consistently lower than the related control values. The behavior of the aberration frequencies in the low-dose region seems to be influenced by the control values, which also depend on the environmental radiation burdens to the donors before blood sampling and thus were significantly affected by the Chernobyl fallout.

Mass Transfer of Diffusive Species with Nonconstant In-Flight Formation and Removal in Laminar Tube Flow. Application to Unattached Short-Lived Radon Daughters

This article deals with convective-diffusive aerosol transport with in-flight formation and removal and is applied to the unattached fraction of short-lived radon decay products. Two novel contributions to previous studies are given in this numerical and experimental work: on the one hand, we solve the mass-transport equations for all the short-lived radon daughters; on the other hand, we include the 218Po neutralization into the mass-transport equation of the first radon decay product. Concerning the mass-transfer of all short-lived radon daughters, numerical calculations lead to the development of simple correlations for the 214Pb and 214Bi penetration fractions. Those correlations can be used to determine the diffusion coefficient of 214Pb and 214Bi using the 2-filter method. In our experiments, a diffusion coefficient equal to 5 X 10-6 m2 s-1 is found for the 214Pb. Concerning the 218Po neutralization, better agreement is observed between our numerical and experimental results when 218Po neutralizatio...

Radon: characteristics in air and dose conversion factors.

The dose conversion factor (DCF) which gives the relationship between effective dose and potential alpha energy concentration of inhaled short-lived radon decay products is calculated with a dosimetric approach. The calculations are based on a lung dose model with a structure that is related to the new recommended ICRP respiratory tract model. The characteristics of the radon decay products concerning the unattached fraction and the activity size distribution of the radon decay products are important input quantities for the calculation of DCF. Experimental data about these parameters obtained from measurements in homes, at working places, and in the free atmosphere at ground level in the last past years are summarized. Taking into account the measured aerosol characteristics the DCF fractions of the unattached (DCFu) and aerosol-attached (DCFae) radon decay products for different places were calculated. Variation of DCF for different places were caused dominantly by the variation of DCFu of the unattached radon clusters (0.3-32 mSv WLM(-1)). Nose inhalation drastically reduced (about a factor 4) the dose contribution by the unattached cluster. The dose fraction by the radon decay product aerosol (DCFae) varies between 4-10 mSv WLM(-1). Taking into account a relative sensitivity distribution between bronchial, bronchiolar and alveolar regions of the thoracic lung with 0.80:0.15:0.05 and nose breathing the DCF of most of the working places (inhalation rate: 1.2 m3 h(-1)) vary between 5.7-6.7 mSv WLM(-1) depending on the number concentration of the aerosol particles. The DCF-value of 4.2 mSv WLM(-1) for the general public in dwellings with higher aerosol concentration (>4 x 10(4) particles cm(-3)) has about the same value as recommended by ICRP 65 (1994b). Significantly higher are the DCF-values for "normal" aerosol conditions indoors (5 x 10(3)-4 x 10(4) particles cm(-3)) and in the open air (7.3 mSv WLM(-1) and 9.7 mSv WLM(-1)).

Overview of Radon Lung Dosimetry

It is widely held that the probability of lung cancer induction following inhalation exposure to ambient radon progeny depends on the cellular dose to sensitive target cells in the bronchial epithelium. The sequence of events, ranging from the inhalation of short-lived radon decay products to the energy deposition at the cellular level, is commonly termed 'radon lung dosimetry'. Its major components are the mathematical description of the morphometry of the human tracheobronchial tree, the deposition of inhaled radon progeny at bronchial airway surfaces during a full breathing cycle, their subsequent clearance from the initial deposition sites competing with radioactive decay, and the dosimetry of alpha particles emitted from these nuclides in the bronchial epithelium. The different modelling assumptions currently used in radon lung dosimetry are here reviewed, confronting the ICRP respiratory tract model with more sophisticated models based on airway generations.

Long term and equilibrium factor indoor radon measurements

This paper presents the annual radon gas concentrations obtained during the 1994–1995 monitoring campaign using passive electret system (type E-PERM). Radon levels were measured in 154 single family dwellings, in normal occupancy conditions (open house condition) in the metropolitan zone of Mexico City. At the same time radon monitoring was performed outdoors. The results show the general log-normal distribution of integrated indoor radon concentration with an annual indoor mean of 3.8 pCi·l−1. The seasonal variations show the minimum mean values in the summer season which are 39% lower than that in autumn. Equilibrium factors (F) were measured in 12 typical houses both in autumn and winter using a continuous working level monitor for short-lived radon decay products and H-chamber loaded with a short term electret (HST, E-PERM) for radon gas. The obtained total mean equilibrium factors are:F=0.41±0.17 andF=0.29±0.04 for indoor and outdoor, respectively. A quality program was also improved.

Inter-comparison measurements of the activity size distribution of aerosol attached short-lived radon decay products in a dwelling located in Brittany

Inter-comparison measurements of the activity size distribution of aerosol attached short-lived radon decay products in a dwelling located in Brittany

Efficient adsorption of waterborne short-lived radon decay products by glass fiber filters.

Glass fiber filters of a certain brand were found to be very efficient (retention > 95%) for adsorption of short-lived radon decay products during filtration of water. Carrier-free samples are obtained in a convenient geometry for efficient gross beta counting. Adsorption of "hot atoms" is not disturbed by the presence of "cold" lead ions. Approximate radioactive equilibrium between radon and its short-lived decay products may or may not exist in water at the source, but does exist after 3 h in PET bottles. These bottles are shown to be gas-tight for radon. Calibration of activity concentration in Bq L(-1) (radon gas concentration approximately equilibrium equivalent radon concentration) was performed by several standard procedures. Limit of detection is 2 Bq L(-1) within 10 min (total time) or 10 Bq L(-1) within 5 min for a net signal of 5 times standard deviation.

The ratio of long-lived to short-lived radon-222 progeny concentrations in ground-level air

The ratio of 210Pb air concentration to the short-lived radon ( 222Rn) decay products concentration at ground level was investigated at a semi-rural location 10 km north of Munich, south Germany, for a period of 11 years (1982–1992). The average ratio from 132 monthly mean values has been found to be (7.5 ± 2.2) × 10 −5 (arithmetic mean ± S.D.). While the time series of the short-lived radon daughter concentration exhibit a distinct seasonal pattern with maxima mostly in October of each year, the course of 210Pb air concentration is characterized by high values from October through February. Consequently, high ratios of 210Pb to short-lived decay product concentration are often observed in the winter months of December–February. To study the influence of meteorological conditions on this behaviour, 210Pb and 214Pb concentrations were measured on a short-term basis with sampling intervals of 2–3 days from October 1991 to November 1992. The air concentrations obtained within those intervals were then correlated with actual meteorological parameters. On the base of this investigation the seasonal behaviour can essentially be explained by the more frequent inversion weather conditions in winter than in the summer months. At the same location, the average ratio of 210Po to 210Pb concentration in ground level air has been found to be 0.079 from 459 weakly mean values between 1976 and 1985. Hence, the corresponding average ratios of the short-lived radon daughters (EEC) to 210Pb and 210Po, were 1:7.5 × 10 −5 and 1:0.6 × 10 −5, respectively.

The Influence of Biological and Aerosol Parameters of Inhaled Short-lived Radon Decay Products on Human Lung Dose

The purpose of this article is to assess the influence of biological and aerosol parameters on human lung dose with regard to a comparison with the corresponding recommended dose values of the International Commission on Radiological Protection (ICRP). The dose conversion factor which gives the relationship between effective dose and potential alpha energy concentration of inhaled short-lived radon decay products (218Po, 214Pb, 214Bi/214Po) is calculated with a dosimetric approach. The calculations are based on a lung dose model with a structure that is related to the recently recommended ICRP respiratory tract model. Because of the short half-lives of the investigated nuclides, simplifying modifications of the model were possible. Firstly, the underlying assumptions of the model are described. Secondly, important input parameters of the model are varied to assess the uncertainty of the dose conversion factor due to the uncertainty of these parameters. The main emphasis is focused on biological and aerosol parameter variability like variation of breathing rate and breathing mode, clearance rates, critical cells for the induction of lung cancer, particle size and dispersion of the activity size distributions. The possible range of dose conversion factors is discussed both for indoor and mine aerosol conditions in the framework of the presented dose model. The investigation shows that the dosimetric approach leads to a dose conversion convention which is a factor of more than two times higher than the recommended epidemiological values of the ICRP of 3.9 mSv.WLM-1 for the public and 5.1 mSV.WLM-1 at working places. The dosimetric results yield both for indoor and mine aerosol conditions, dose conversion factors in the range of 10 mSv.WLM-1 to 15 mSv.WLM-1 depending on breathing mode.

Gamma radiation and radon levels in Mexico City dwellings

Gamma exposure rate and radon levels were measured in 75 single-family dwellings in Mexico City in order to correlate them with local environment. Radon monitoring was performed both indoors and outdoors using a continuous working level monitor for short-lived radon decay products; the gamma exposure rate was measured using CaSO4: Dy+PTFE. The results obtained show a log-normal distribution. The mean indoor radon concentration is lower than 45 Bq/m3 and the mean indoor gamma exposure rate was 11.29 μR/h.

Size Distribution of Unattached and Aerosol-Attached Short-Lived Radon Decay Products: Some Results of Intercomparison Measurements

Abstract Within the framework of radiation protection programmes supported by the CEC, the US-DOE, and the Australian Government, intercomparison measurements were performed in a house with elevated radon concentrations in Northern Bavaria (Germany) in October 1991. Besides the research aspects of aerosol sciences, the purpose of this joint measurement was to compare dose conversion factors calculated from the results obtained by these three laboratories. In low ventilated rooms with moderate aerosol particle concentrations (Z=4000-8000 cm-3) about 40% of the 218Po activity is associated with clusters, narrow in shape (sg&lt;1.2) and with a median diameter of 0.9 nm. There are strong indications for an additional, fairly broad mode (sg&gt;1.2, fraction=10%) of the 'unattached' part of the 218Po distribution with a median diameter of 3-4 nm. The averaged mode (3 days) derived effective dose conversion factors (HE-DCF) from the 218Po values - measured by the three groups - differ less than 30%. However, the daily averaged values sometimes differ by a factor of 2. In general, it does not appear to make much difference to the derived conversion factors if the ultrafine mode (&lt;10 nm) is unimodal or bimodal. The median diameters of the aerosol-attached fraction of the short-lived radon decay products ranged between 200 and 350 nm, depending on the different methods used by the three laboratories. However, these fairly large differences have only little influence on dose conversion factor calculations. This joint exercise clearly showed that accurate particle size measurements in the diameter range 10-100 nm (nucleus mode), which requires combining impactors and diffusion battery techniques, is a difficult task, not fully solved as yet.

Size Distribution of Unattached and Aerosol-Attached Short-Lived Radon Decay Products: Some Results of Intercomparison Measurements

Size Distribution of Unattached and Aerosol-Attached Short-Lived Radon Decay Products: Some Results of Intercomparison Measurements

08.O.02 Size distribution of “unattached” short-lived radon decay products in dwellings

08.O.02 Size distribution of “unattached” short-lived radon decay products in dwellings

Radon ( 222Rn) short-lived decay products and their temporal variation in surface air in Tripoli

Average monthly morning radon activity concentrations in surface air in Tripoli, based on measurements of short-lived decay products, are reported for the period from January to December 1985. Monthly averages ranged from 2.42 to 5.0 Bq m −3. The data suggest that the maximum occurs from October to February and the minimum from March to July. The annual mean activity concentrations (Bq m −3) of short-lived decay products were 2.0 for 218Po, 1.80 for 214Pb, and 1.72 for 214Bi. All values were found to be normally distributed. The annual mean values of activity concentration ratios for 214Pb/ 218Po, 214Bi/ 218Po, and 214Bi/ 214Pb are 0.91, 0.87, and 0.9, respectively.