Radon: is it a problem?

Radon gas is a major source of radiation exposure to the general public. Radon-222 is a product of uranium-238, present in varying concentrations in all soils. Radon enters buildings from soil, water, natural gas, and building materials. Its short-lived breakdown products, termed "radon daughters," include alpha-emitting solids that can deposit in the lungs. Firm evidence links lung cancer risk in miners with high exposure to radon daughters. The amount of risk associated with the much lower but chronic doses received in buildings is difficult to establish. By some extrapolations, radon daughters may be responsible for a significant number of lung cancer deaths. The existence or extent of synergism with smoking is unresolved. Local conditions can cause high levels of radon in some buildings, and measures that reduce indoor radon are of potential value.

Lung carcinomas in Sprague-Dawley rats after exposure to low doses of radon daughters, fission neutrons, or gamma rays

The effectiveness of radon-daughter inhalation and irradiation with fission neutrons and gamma rays in the induction of lung carcinomas in Sprague-Dawley rats at low doses is compared. Earlier reports which compared radon-daughter inhalations and neutron irradiations over a wider range of doses were based on dosimetry for the radon-daughter inhalations which has recently been found to be faulty. In the present analysis, low-dose experiments were designed to derive revised equivalence ratios between radon-daughter exposures, and fission neutron or gamma irradiations. The equivalence is approximately 15 working level months (WLM) of radon daughters to 10 mGy of neutrons (the earlier value was 30 WLM to 10 mGy). The relative biological effectiveness (RBE) of neutrons is 50 or more at a gamma-ray dose of 1 Gy. In these experiments with low doses and exposures, the lifetime incidences can be estimated from the raw incidences, while the derivation of the time dependence of the prevalence is essential for the estimation of RBE values and equivalence ratios.

[Background of low-level gamma-ray spectrometer due to the atmospheric 220Rn and 222Rn]

In connection with low-level gamma-ray counting of natural samples, background due to 220Rn- and 222Rn-daughters was monitored. The results obtained for 4 months showed that the background gamma-ray from 222Rn-daughters was more variable than that of 220Rn-daughters. An efficient air-conditioning was helpful to keep the background stable. It was practically equivalent to the use of N2-gas. Radiometric data for dust samples filtered from the laboratory air suggested that Rn-daughters tended to be removed by air-conditioning.

Health assessment of environmental pollutants: proliferative and degenerative diseases

In order to achieve a balanced approach to risk assessment between carcinogenic and non-carcinogenic health effects one must examine the risk of disease or death in the general population exposed to a particular air pollutant that can be related quantitatively to intensity and duration of exposures (National Academy of Sciences, 1983). Such risk assessment should be based upon careful evaluation of scientific findings of dose-response relationships in the chronically exposed population. Quantitative assessment of environmentally produced disease in man has proven to be complex and demanding. A variety of factors play important roles in this task. As an example, there are induction-latency periods for chronic diseases, including cancer, which may range from five to twenty-five years. The diseases themselves, whether proliferative or degenerative, may follow several stages of progression. There is only sparse epidemiological data on serious health effects that may be due to environmental as compared to occupational exposures. Exposures to chemical or radiological air contaminants do not occur singly but to a multiplicity of agents, and disease processes are frequently markedly affected by the interaction of a variety of factors, particularly that of cigarette smoking. There is growing recognition of potentially sensitive subpopulations, including the elderly and the very young, but adequate techniques for assessing the magnitude of increased risks to these groups have not yet been developed.

Radiation doses from radon in buildings

Not until about 1970 was it possible to estimate the magnitude of the correlation between additional lung cancer frequency and radon daughter exposure in miners. In addition, it has been realised that high levels of radon daughters in homes may be found in all countries and therefore the interest in radon in buildings has rapidly increased during the last 10 years. Radon gas enters the house from underground, from building materials and in some cases from tap water. Indoor radon daughter concentrations vary between countries and regions. The absorbed dose in the basal cells of the bronchial epithelium based on an average of the population in Canada, U.S.A. and West Germany can be estimated to be about 1 mGy a-1 (average radon daughter concentration about 25 Bq m-3) for Great Britain about half of that value and for the Nordic countries about double this value. 300-3000 lung cancer cases (most probable 1100) may occur in the future in the Swedish population of 8.4 million from radon daughter exposure indoors today. This estimation is made by the National Institute of Radiation Protection. A lower estimate of 100-1000 lung cancer cases is made by the Swedish Cancer Committee. Efforts to decrease the exposure from radon daughters indoors have been made in some countries by establishing limits or recommendations for the radon or radon daughter concentration indoors. Measuring methods for finding houses with high radon daughter concentrations and effective building techniques in order to decrease the radon daughter concentrations in both existing and for planned buildings are available.

Radiation in dwellings and cancer in children

Indoor radiation, especially radon exposure, has been in focus in the public domain during the past several years. The growing concern among parents of children with cancer possibly having high radiation levels in their homes led us to study the levels of gamma- and alpha-radiation levels in the homes of a group of children in the county of Ostergötland. The indoor concentration of alpha-emitting radon daughters was measured by a high-voltage method. The gamma activity was measured with a standard detector scintillation meter. The yearly average for radon-daughter concentration in both cases (57 Bq/m3) and controls (61 Bq/m3) corresponds fairly well with the national average of 53 Bq/m3. The yearly average for gamma radiation (cases 0.37 mGy, controls 0.36 mGy) is much lower than the permissible upper level in dwellings (2.5 mGy/year). The values seem to be of the same order as the subtracted cosmic radiation, which is 0.24-0.26 mGy. No appreciable difference could thus be found between cases and controls either from gamma radiation or radon-daughter exposure. We cannot from our study rule out the possibility of an effect of low-level radiation in susceptible individuals, but it seems clear that children who get cancer do not live in more radioactive homes than other children.

[Radiation exposure and risk of radon in the room air of Swiss houses]

The radioactive noble gas radon, a member of the natural decay chains of uranium and thorium, enters the indoor environment in regionally highly diverging amounts. Subsoil of dwellings, building materials and drinking water are the main sources. In Switzerland and in many other countries, exposure of the lung tissue to the short lived radon decay products is the most important component of the radiation dose of the general public. Annual doses in areas with crystalline rock of high uranium content may reach the limits set up for occupational exposure. However, a clear link between cumulative exposure to radon daughters and elevation of the lung cancer incidence exists only for underground miners. The majority of human epidemiological studies point to a linear dose effect relationship. The indoor radon levels are determined by geology, building materials and techniques, climate and behaviour of the occupants. Experiences from Scandinavia and the Northern parts of America clearly indicate the possibility of cost-efficient remedial measures to reduce indoor radon levels.

Radon-222 concentrations and decay-product equilibrium in dwellings and in the open air

Results are presented of measurements of the activity concentrations of 222Rn and its short-lived decay products and the 212Pb/212Bi concentrations in more than 200 dwellings in West Germany and in the open air. For more than 130 measurements of the equilibrium factor F in dwellings the median value was found to be 0.3. Measurements of F in the open air under various conditions resulted in a mean value of about 0.4. The results of the investigations showed that indoors F depends only slightly on ventilation, indoor 222Rn concentration and other parameters. The equilibrium factor F in the open air, however, was found to depend on meteorological conditions. Empirical correlations from the data obtained for the daughter/222Rn concentration ratios were derived to provide relations for the prediction of the individual daughter product concentrations at a measured 222Rn level. It was established that the daughter/222Rn concentration ratios for indoor air do not change within the range of 222Rn concentrations investigated (1-370 Bq X m-3). These relations, however, are not valid for the daughter/222Rn concentration ratios in outdoor air. The correlations derived further suggest that the individual daughter product concentrations may be assessed with sufficient accuracy by only measuring the 222Rn concentrations. Thus the daughter ratios obtained in this way should enable good estimates of the lung dose for members of the public due to inhalation of the short-lived 222Rn daughters and the dose contribution of the individual 222Rn-daughter products.

Theory of passive measurement of radon daughters and working levels by the nuclear track technique

A theoretical basis is described for long-term measurement of the activities of the alpha emitters in air by the track-etching technique. Inference of the other activities allows working levels to be derived. A set of absorber foils allows the differing response to alpha particles of different energies to be used to identify the relative abundance of the alpha emitters and the importance of diffusion to surfaces. The method is appropriate to measuring long-term exposures to radon atmospheres in homes or mines.

Relationship between the 210Pb content of teeth and exposure to Rn and Rn daughters

Existing data on 210Pb in human teeth are reviewed for various countries. The mean value of 210Pb in the teeth of population groups exposed to "normal" levels of radon-daughter exposure is about 2 mBq/g. A detailed analysis of 48 samples from a "normal" Italian population group revealed that smoking habits and age may have some influence on 210Pb content of teeth, while this is not the case for differences in sex. A group of 45 Austrians exposed to elevated levels of radon and radon daughters is compared with the Italian group. After subtraction of background levels of 210Pb as found for the normal Italian population, the incremental 210Pb tooth content due to excessive radon-daughter exposure has been correlated with the individual cumulative exposure corrected for background radon-daughter exposure. A statistical analysis shows the significance of the linear correlation at the alpha = 0.01 level. For the incremental increase of 210Pb in teeth, a value of 1.2 mBq/g has been used for a lifetime exposure to 1 WLM. This result is compared to corresponding data published in the literature, which are predominantly related to the 210Pb content of bone after short-time exposure at high levels, e.g. in uranium mines. The comparison seems to indicate the influence of the exposure rate and the need for a comprehensive model, which takes into account radon-daughter inhalation, radon dissolved in body fluids and 210Pb metabolism.

Measurements of radon-daughter concentrations in and around dwellings in the northern part of The Netherlands; a search for the influences of building materials, construction and ventilation

The concentration of radon daughters has been determined in and around 80 dwellings located in the northern part of the Netherlands by using a one-filter method. Median values of 2.0 and 0.4 mWL were measured for the indoor and outdoor concentrations, respectively. The average outdoor concentration was about an order of magnitude higher for wind directions between SE and SW than for SW-NW. On the average, dwellings with double-pane windows and/or concrete floors were found to have significantly higher radon concentrations than those with single-pane windows and/or wooden floors. For the living room of a particular dwelling 18 measurements were carried out. The data for this dwelling indicate a linear relation between the concentration indoors and outdoors with a slope of 3.8 +/- 2.0. This unexpected behaviour is thought to be related to ventilation via the crawl space. Measurements of ventilation patterns and measurements of radon concentrations in the living room and the crawl space are consistent with this picture.

Passive measurement of working levels and effective diffusion constants of radon daughters by the nuclear track technique

Measurements were made of working level ratios and the effective diffusion constants of radon daughters using a special housing designed to provide a uniform diffusional environment at the passive detectors. For 2 of 7 exposures, the measured scale of the diffusion was too large to satisfy the uniformity requirement. For the other 5, it was satisfied and reasonable working level ratios (WLR) were obtained. Such a housing could be used for extended area working level measurements but is too bulky to be suitable for personnel dosimetry. Personnel dosimetry could be done in mines using a passive area measurement of WLR combined with individual passive 222Rn measurements.

Lung cancer in Swedish iron miners exposed to low doses of radon daughters

In a retrospective study, we investigated lung-cancer mortality from 1951 to 1976 in 1415 Swedish iron miners exposed to short-lived radioactive daughters of radon gas at concentrations leading to annual doses close to the currently accepted occupational limit. Fifty deaths from lung cancer were observed, as compared with 12.8 expected; expected rates were determined by a smoking-specific analysis based on data from a random sample of the Swedish male population. Among nonsmokers 18 deaths were observed, as compared with 1.8 expected; among current smokers and recent exsmokers 32 deaths were observed and 11.0 were expected. The effects of smoking and exposure to alpha radiation from radon daughters were nearly additive. Comparison of lung-cancer risk coefficients from this study and from other cohort studies of underground miners showed good agreement. Exposure to radon daughters is a major medical problem is underground metal mining, but our results also indicate that exposure to radon daughters at home accounts for an appreciable number of cases of lung cancer in the general population.

A comparison of alpha spectroscopy and gross alpha techniques for determining working level in uranium mines and houses

We have completed an evaluation of two methods that estimate potential alpha energy of radon daughters suspended in air. One method approximates Working Level from a single measurement of gross alpha activity using a generalization of procedures originally described by Kusnetz and Rollé. The second is a linear combination of the count rates from RaA and RaC' determined from a single measurement using alpha spectroscopy as originally suggested by Schiager . These methods were compared in terms of precision and accuracy for a range of radon-daughter concentrations. Even though alpha spectroscopy provides information on two independent variables, it does not always improve the accuracy and precision of the estimate of Working Level in uranium mine atmospheres and houses.

Time variation of radon daughters concentration in snowfall

Time variation of radon daughters concentration in snowfall was measured continuously. The relations of radon daughters concentration in snowfall to the precipitation and to atmospheric radon daughters concentration were investigated. It has become clear that when precipitation is small, radon daughters concentration in snowfall is distributed in a wide range, and that the quantity of radon daughters brought to ground surface by snowfall is proportional to precipitation. Washout effect of the snowfall on atmospheric radon daughters was also investigated.

Ambient monitoring of airborne radioactivity near a former thorium processing plant

Twenty-four hour sampling for airborne radioactivity near a former thorium and rare-earth extraction facility was conducted for approx. 2 months with high-volume and dichotomous air samplers. Thoron ( 220Rn ) daughters were identified in the air and confirmed to be originating from the waste storage site. High-volume samplers near the facility measured average 212Pb concentrations of 177, 43, and 237 pCi/m3 with corresponding ranges of (1.9-1351), (1.5-301) and (0.73-2201)pCi/m3. Simultaneous measurements with dichotomous samplers at the same sites measured average 212Pb concentrations on coarse particulates (2.5-15 microns dia.) of 14, 4 and 10 pCi/m3 and on fine particulates (less than 2.5 microns dia.) of 94, 9 and 214 pCi/m3, respectively. Corresponding ranges were (0.2-109), (0.1-63) and (0.1-94) pCi/m3 for coarse particulates and (0.7-1094), (0.4-101) and (0.5-2685) pCi/m3 for fine particulates. Uranium, thorium and radium radionuclides were not identified as being present in significant concentrations in the particulate samples.

An electrostatic precipitator for the study of airborne radioactivity

An system has been developed to measure airborne radioactivity using electrostatic precipitation for collection and alpha-particle spectroscopy for detection. Features include good energy resolution (e.g. 170 and 300 KeV for full-width half maximum and full-width tenth maximum for 7.7-MeV alpha particles using a 7-cm2 area detector; and 52- and 122-KeV, respectively, using 1.2-cm2 area detector) and versatile computer control for collection, counting and data reduction. Aerosols bearing the radioactive atoms are deposited on a foil tape by electrostatic precipitation for a predetermined time after which the foil is moved under a solid-state detector to count the alpha-particle emissions. Activities are determined at the same frequency as samples are collected. Helium gas can be introduced at the detector to reduce energy loss and improve resolution. Although in principle certain aerosol sizes could be difficult to collect, in practice no difficulties were observed for typical environmental conditions, provided sufficiently low air-sampling rates were used. One important application is the measurement of 222Rn daughters. The sensitivity is such that detection of individual daughter concentrations less than 0.1 pCi/l. with only a 10% counting error is possible.

Optimizing the total-alpha three-count technique for measuring concentrations of radon progeny in residences

A technique for measuring 222Rn-progeny concentrations in air, involving counting alpha decays for three intervals on a filter through which air has been drawn, is optimized for measuring low concentrations typically found indoors. Sampling and counting intervals are selected to minimize a linear combination of the minimum measurable concentrations (MMCs)--concentrations at which the relative standard deviation in the measurement due to counting statistics is 20%. The effects on the MMCs of varying total measurement time, sampling and delay times, and of radon-progeny activity ratios are considered. The effect on measurement precision of variations in the collection rate of radon progeny on the filter is also evaluated. Previous work on this technique has often focused on measurements in uranium mines where concentrations of radon progeny are typically much higher than in residences. With sequential sampling and counting intervals, extending the total measurement time from 35 to 60 min reduces the MMCs by factors of 3, 7 and 4 for 218Po, 214Pb and 214Bi, respectively, thereby permitting precise measurement of indoor concentrations down to the order of one pCi/1. By employing an instrument that counts while sampling, the MMCs can be further reduced by factors of 5.5 for 218Po, 2 for 214Pb and 2.5 for 214Bi, again for a 60-min measurement period.

Radon-222 and progeny measurements in "typical" East Tennessee residences

Modified Wrenn chambers for continuous monitoring of 222Rn, featuring several improvements including a computer-assisted electronics package, have been developed at the Oak Ridge National Laboratory. A field test of these instruments was conducted by placing them in the homes of staff members. Field testing was conducted in seven houses for periods ranging from 4 to 18 days. During this testing period, the 222Rn concentration in these houses was monitored continuously. Radon-222 concentrations in the basements of three of the seven houses were in excess of 100 Bq/m3 almost continuously. One residence had instantaneous concentrations approaching 1000 Bq/m3. Samples of soil and building materials from these residences indicated that 226Ra concentrations were in the normal range (40 Bq/kg). Radon progeny measurements were made in five of these houses on a "typical" day. Results obtained were as follows: for basements, a geometric mean of 0.016 WL (geometric S.D. of 2.9); for upper floors a geometric mean of 0.014 WL (geometric S.D. of 2.9). This paper summarizes the results obtained in the field test.

The indoor concentration of radon daughters in three different areas of the U.K

The concentrations of radon daughters were measured in 86 rooms in three different areas in U.K.: Birmingham, Aberdeen and mainland Orkneys. The geometrical means of the concentrations in these areas were found to be 2.0, 6.7, and 2.5 mWL, respectively. In many cases, the ground beneath the houses was an important source of radon; where there was good sub-floor ventilation, the ground contribution was not important.

[Radiation exposure of the respiratory tract to radionuclides in the environment]

Epidemiological investigations concerning lung cancer mortality of miners in radioactive underground climate have clearly resulted that the alpha-radiation of radon daughters emerging from the geological formations represent the causative factor for the accumulation of these lung cancers. The same radionuclides are also important as components of the natural radiation exposure, above all in houses built with radium containing material. Estimations of the risk referring to this form of natural radiation exposure allow rough calculation of its role for lung cancer incidence in GDR. Accordingly about 10%, in men 5% and 50% in females, of the cases of lung cancer may be caused by the natural inhalative radiation exposure. Natural radioactivity by coal and coal ashes as well by tobacco smoke are shortly outlined in their additional significance. The measures of radiation protection legal in GDR to limit inhalative exposure, above all in buildings, by supervision and selection of building material are described.

A study of radiation parameters in an open-pit mine

Radiation parameters associated with the open pit mining of a small (10,000 tonnes), but high grade (2%) uranium deposit at Nabarlek, N.T., have been investigated in detail. External radiation levels, radon emanation rates and radon daughter levels were measured systematically during the development of the mine, and are correlated with ore grade, properties of the host rock and atmospheric conditions. Significant radon daughter concentrations were observed only under stable atmospheric conditions, usually during the might and were invariably associated with thermal inversions. The mean cumulative exposure to radon daughters was estimated from the measured levels to be 0.065 Working Level Months for employees working in the pit for the entire four and a half months of mining. The mean cumulative external gamma ray exposure for the same employee group was measured using thermoluminescent dosimeters to be 2.3 mSv (230 mrem). For most other employees, however, exposures were much lower. Data on long lived radionuclides in dust and on particle size distribution are also presented.

Dose conversion factors for radon daughters in underground and open-cut mine atmospheres

As uranium will be mined in Australia by open-cut methods, previous work on calculating dose conversion factors for radon daughters has been re-examined. The fractions of radon daughters deposited on lung airways and the factors for converting from equilibrium activity of radon daughters on airways to dose to basal cells are re-calculated. The variation around these estimates through variability of lung morphology and the depth of the basal cells is discussed. Average dose conversion factors calculated for atmospheres which may be typical of underground mines range from 12 mGy/WLM to 33 mGy/WLM. Use has been made of measurement results on unattached fraction at an open-cut mine in the Northern Territory, Australia, to derive dose conversion factors, ranging from 50 mGy/WLM to 135 mGy/WLM which are applicable to this environment.

Dose calculations for the respiratory tract from inhaled natural radioactive nuclides as a function of age--II. Basal cell dose distributions and associated lung cancer risk

Dose calculations for inhaled radon decay products presented in Part I (Ho79) have revealed that the doses to tracheobronchial and pulmonary compartments of the ICRP lung model are significantly dependent on age. From a consideration of the nonuniform dose distribution within the tracheobronchial region, doses are now calculated for the bronchial epithelium basal cells which are commonly regarded as the critical target for the induction of lung cancer. For the simulation of deposition and clearance mechanisms a refined mathematical model for postnatal growth of the human respiratory tract was developed on the basis of the Weibel model A. A reference atmosphere of 1 pCi/l for each nuclide with a mean respiratory minute volume, corresponding to a mean physical activity, was used to determine doses for the basal cells in different generations of the tracheobronchial tree as functions of age. The results obtained show again a strong dependence on age. In general a continuous decrease of dose with increasing age can be seen, with distinct differences between the various generations. If, however, the physical activity distribution and the ratio for the decay products as already defined in Part I are used, maximum dose values appear again in all generations at the age of about six years. Application of data on the relative risk of the induction of various malignancies versus age, taken from the BEIR report, results in even more pronounced dose maxima with a significantly higher radiation risk for children between birth and ten years of life of about one order of magnitude as compared to adults.

An evaluation of unattached radon (and thoron) daughter measurement techniques

The collection efficiencies of parallel plate, inertial impactor and wire screen devices reported in the literature for measurement of the unattached fraction of radon (or thoron) daughters are calculated for collection of the attached fraction of the aerosol, using real uranium mine aerosol activity-size distributions. The attached activity collection efficiencies may be as much as 4.3%, which, given the typically low values of the unattached fraction (a few per cent), results in a very substantial error in the measurement of the latter. Published unattached fraction measurements in the environment may therefore be high and should be interpreted with care.

Environmental radon daughter alpha dose factors in a five-lobed human lung

The alpha dose from 222Rn daughters per unit exposure (rad per WLM or rad per year per pCi 222Rn/m3) to basal cells in bronchial epithelium in a five-lobed human male lung is calculated. These factors are then derived for women, children and infants by scaling the dimensions of the male lung. The 222Rn daughter characteristics chosen are those typical of environmental atmospheres. Both active and resting breathing patterns are utilized in the calculations to yield the overall dose per unit exposure in typical population exposures.

An optimized scheme for measurement of the concentrations of the decay products of radon and thoron

Radon daughter measurement methods have not previously been fully optimized in the presence of thoron daughters, the presence of which leads to an increase in the total potential alpha energy. Taking into account the fluctuations associated with flow rate and concentration as well as the statistics of decay, optimized counting schemes were determined for the daughters of radon and thoron for different sampling times over a wide range of counting intervals. The counting schemes examined were optimized for maximum precision. Counting schemes corresponding to impractically long counting intervals, and counting times which required measurements beyond an 8 hr working shift were rejected. Under these constraints the most appropriate sampling time was found to be 10 min.

Radon daughter exposure to uranium miners

Radon exposures to U.S. uranium miners under present conditions average about 1.3 WLM per year approximately or equal to 60 WLM per full working lifetime. This is intermediate between (a) the lowest exposures for which there have been excess lung cancers reported among U.S. miners (120-240 WLM) and (b) average environmental radon exposures (16 WLM), so models based on these two situations are used to estimate expected effects on present uranium miners. In Model A, the loss of life expectancy is 45 days, the SMR (standardized mortality ratio) for lung cancer is 1.10, and the SMR for all causes between ages 18 and 65 is 1.013. In Model B these are 10 days, 1.03 and 1.002 respectively. It is shown that the radon exposures to miners are similar to those to millions of Americans from environmental exposure, and that miner health risks are comparable to those of other radiation workers. Their lung cancer risk from radon is 7-50 times less than their job-related accident mortality risk, and represents 0.7-4% of their total risk in mining. Miners suffer from many diseases with SMR very much larger than that for radon-induced lung cancer, and there are many other occupations and industries with far higher SMR for lung cancer than that from radon exposure to miners.

Radon daughter equilibrium and unattached fraction in mine atmospheres

Measurements of the equilibrium between radon and its daughters in mine atmospheres are presented. The situation in mines seems to be too complex to be described by any simple theoretical model. There is however a good correlation between the equilibrium factor, F, and the individual daughter ratios. This suggests that the individual daughter concentrations may be assessed by Kusnetz-measurements of the equilibrium factor, F. Measurements by the wire screen method indicate that the dust concentration is the main influencing factor upon the unattached fraction of the radon daughters. The unattached fraction of the potential alpha-energy was lower than 0.05 in most mining situations. In areas with very clean air, the unattached fraction may however be higher than 0.3. Measurements indicated a good correlation between the unattached fraction of the potential alpha-energy and the unattached fraction of the individual daughter products. This suggests that assessments of the unattached fraction of the individual daughters may be obtained by using the Kusnetz method for measurements on the screen and back up filter.

Cellular lung dosimetry for inhaled radon decay products as a base for radiation-induced lung cancer risk assessment. I. Calculation of mean cellular doses

Lung cancer induction is commonly regarded as the most important somatic risk arising from the inhalation of radon and its decay products. Relating carcinogenesis to radiation exposure needs a detailed knowledge of the cellular dose distribution in the human respiratory tract. Different dosimetric models have been developed for the determination of cellular doses, particularly for the basal cells of the bronchial epithelium which are considered as the critical cells for lung cancer induction. Part 1 of the paper describes the influence of various environmental as well as anatomical and physiological factors on the resulting dose. Significant inter- as well as intra-subject variabilities of structural components of the human lung, respiration characteristics and clearance mechanisms demonstrate the necessity of applying stochastic models in lung dosimetry.