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The Jacobi Room Model is applied to fit radon daughter concentrations measured in a room. The aerosol size distribution and ventilation rate are measured simultaneously. The mean deposition rate fitted to these experiments is 16 h-1. Once all parameters are fixed, the unattached fraction and the effective dose equivalent are calculated, and are put in perspective to the Working Level concept.
Results are presented of the influence of the particle concentration on the activity concentrations of the attached and unattached shortlived radon daughters. The measurements were carried out in rooms of houses in Southern Germany with radon activity concentrations in the range of 150-900 Bqm-3. Consideration of the F factor and the fraction of the unattached daughters fp and comparison with theoretical predictions is one part of the data evaluation. In low (v less than 0.3 h-1) and moderate (0.3 h-1 less than v less than 1 h-1) ventilated rooms the particle concentrations (3*10(-3) - 4*10(4) cm-3), F values (0.2 - (0.2 - 0.3) and the unattached fraction fp (0.05-0.15) were measured. Only rooms with higher particle concentrations or with larger particle sizes due to special aerosol sources (cigarette smoke, cooking, stove heating) showed fp-values less than 0.05. In a second part the attachment rate, the plateout rates and the average attachment diameters of the room aerosols were derived from the measured data by model calculations.
Radon and radon daughter concentrations have been measured in 33 "energy-efficient" homes in a small subdivision in Kanata, Ontario. Integrated radon measurements were determined over three month periods for a year using solid state nuclear track detectors. Radon and radon daughter grab sample determinations were made during corresponding periods and confirm the distributions of the integrated radon measurements. Annual average individual home radon concentrations show an 8 fold concentration range between homes. This variability in radon concentrations is not reflected in the range of air exchange rates for the homes. A distinct seasonal variation is noted for the median values of the radon and radon daughter concentrations and the equilibrium factor F in the dwellings.
In the last two decades many countries started national or regional surveys to assess the average exposure to natural radiation of the general public. Survey programmes for external radiation as well as for radon and decay products have been performed are still in progress or will be started in the near future. The paper discusses briefly technical and organisational aspects of survey measurements as well as practical experiences and results available from national or regional survey programmes.
The results of our investigations in the Federal Republic of Germany on the indoor and outdoor exposure to natural radiation from gamma rays and radon and thoron daughters are presented. Indoor the median Rn-222 concentration was approximately four times higher than outdoors. A correlation analysis of the data obtained showed that indoors the equilibrium factor F is almost independent of ventilation, Rn-222 concentration and other parameters. The mean equilibrium factor was measured to be F = 0.3 in dwellings and approximately F = 0.4 outdoors. The results of our investigations on diffusion coefficients and exhalation rates showed, that the activity concentration in dwellings and in cellars can generally be explained by the radon exhalation from the building materials. Only in areas of high radon concentrations, the exhalation from the soil was a decisive factor. The mean effective dose equivalent by residence in dwellings amounted to 0.2 - 0.8 mSv/a for Rn-222 daughters and approximately 0.1 mSv/a for Rn-220 daughters. A relationship has been derived which permits the calculation of the expected average radiation exposure in dwellings by gamma radiation and by radon inhalation as function of the radionuclide concentration in building materials.
A large-scale radon survey has been carried out in the Federal Republic of Germany. Results of measurements in almost 6000 homes are briefly discussed.
Solid state nuclear track detectors were used in a regional survey of radon in indoor air. The study area comprises seven rural municipalities and two towns in an area of 80 X 50 km2 with a population of about 65,000. Measurements were made in 754 houses in 31 subareas. The highest and lowest subarea means were 1,200 Bq/m3 and 95 Bq/m3, respectively. The estimated mean for the whole area was 370 Bq/m3. The concentrations 2,000 Bq/m3 and 800 Bq/m3 were exceeded in 32 and 90 houses, respectively. The present lung cancer incidence does not differ significantly from the national mean.
The principal results of a preliminary study made on indoor radiation levels in Ireland are presented. During the period 1983-84 measurements were made in over 250 houses. Most measurements were made using passive devices: TLDs for penetrating radiation and CR-39 alpha track plastic detectors for radon measurements. The median value of the doses from penetrating radiation was 0.78 milligray/year with a maximum value of 1.47 m Gy/year detected. The radon concentrations showed a large degree of variability with a median value of 43 Bq/m3. About 10% of the houses had radon air concentrations in excess of 100 Bq/m3 with a maximum of 700 Bq/m3 being recorded. A tentative analysis of the data with regard to the geological situation is presented.
An investigation is being developed by the Comitato Nazionale per la Ricerca e per lo Sviluppo dell'Energia Nucleare e delle Energie Alternative, ENEA, to assess the indoor exposure of the Italian population. The programme, which started in 1982, includes regional and local surveys in all the administrative districts and intensive investigations of factors which influence indoor radon levels. The survey is organized by statistical areas of sampling to obtain representative samples of houses. The definition of the areas takes into account basic parameters e.g. geolithological environments, radon soil gas from underlying soils and rocks, specific activities of local building materials, climatic and seasonal variations, building technology, types of houses and town planning. The collected data may also be used for the compilation of radon risk maps to plan special monitoring and remedial actions if needed. Preliminary results concerning the above items are discussed.
Results of a preliminary national survey on radon in houses in Belgium are presented. The indoor radon concentration was determined in 1983 in 79 houses with passive integrating detectors. In 77 of the examined cases the radon concentration is less than 250 Bq/m3. The highest reported value is 330 Bq/m3. The frequency distribution is found to be log-normal with a geometric mean of 41 Bq/m3 and a geometric standard deviation of 1.7. The influence of some human and environmental parameters is also studied. Because of the limited scale of the pilot study only a tendency can be derived.
A pilot study was carried out to establish techniques and procedures for the measurement of indoor radiation in Denmark. A passive cup dosemeter was designed containing CR39 track detectors and TLD's to measure radon and external radiation, respectively. A total of 82 dwellings were selected covering most regions of the country. The dwellings were monitored in two three-month periods, one in winter and the other in summer. The average dose rate in air from external radiation was 0.09 muGy h-1. In the winter the average radon concentrations were 88 Bq m-3 and 24 Bq m-3 for single-family houses and flats, respectively; and in the summer the corresponding values were 52 Bq m-3 and 19 Bq m-3.
This work is related to the problem of providing a more careful evaluation of the population exposure to natural radiation background, and was carried out in connection with the ENEA programmes on the assessment of indoor exposure doses in Italy. A large number of works in recent years have pointed out the main contribution of the indoor dose to the natural dose received by the members of the general population, and the large contribution of radon daughter inhalation. Different building materials and techniques lead to different exposure doses. In Milano such materials can be quite different in kind (bricks, concrete, gypsum by-products, tile-stone, paving-tile, etc.) and origin (national and foreign). For this reason, a collection of indoor doses in Milano is not only complementary to analogous investigations carried out in other Countries of the European Communities, but the obtained information can be compared with other large European towns. As agreed, a large number of various dwellings in Milano were investigated to evaluate the external gamma-ray exposure rate, and measurements of indoor radon concentrations were performed for some of them. Various typical building materials used in Lombardia were also analysed by means of gamma-ray spectrometry.
An indoor survey in order to estimate the population exposure in five towns of an Italian Region is presented. A particular methodology for the campaign was planned and is being applied. Gamma spectrometry of building materials, exposure rate measurements indoors and outdoors and radon concentration measurements indoors were taken with different techniques. A correlation was found between mean gamma exposure rate and mean radon concentration in the houses investigated. An evaluation of mean effective dose equivalents for the inhabitants of the five towns is reported.
The accuracy and variance of passive integrating detectors for radon and radon daughters presently in use in Sweden have been studied. Sets of 10 of each participating detector were exposed in an occupied dwelling. The results were compared with accurate measurements made with instruments from the National Swedish Institute of Radiation Protection. The results from the first test, in the summer of 1983, became an incitement to improved calibration procedures for some of the participating detectors. The test was repeated in February - April 1984. The results showed that all detectors participating in the test and presently in general use in Sweden are reasonably accurate.
Two methods for measuring indoor radon concentrations using activated charcoal have been tested. The first method is the well-known technique with direct gamma-measurements on the exposed canister after the sampling period. The other method uses a thermoluminescence dosemeter placed in the charcoal canister, giving an integrated value of the radon concentration.
To estimate the amount of radon gas transferred from the water to the indoor atmosphere of dwellings in the Swiss Central Alps, the radon concentrations of tap water of about 50 public water supplies were analysed. The radon levels of water in alpine communities fit a lognormal distribution with a geometric mean of 26.5 Bq/1 and a geometric standard deviation of 3.15. Radon monitoring in typical homes in the Swiss Midland revealed a significant influence of wind velocity and temperature difference indoor/outdoor on the indoor radon-daughter levels during the winter period.
A survey of radon concentrations in Dutch dwellings reveals a median value of 24 Bq/m3, while no excessive high values were observed. Correlations between radon concentration and (combinations of) building parameters will be presented and discussed in terms of the various sources of indoor radon.
An estimate has been made of gamma doses to the population in the Netherlands, caused by natural radiation sources encountered in the environment. Data are given, derived from two independent types of measurement: Exposure/dose rate measurements in the living environment (private houses as well as workplaces), using a high pressure ionization chamber and thermoluminescent dosemeters (TLD) respectively and Individual monitoring, using TLD. The study included some 750 individuals, 400 houses and 275 workplaces. The participants were selected and divided into two groups on the basis of their location in areas of relatively high and low terrestrial radiation level respectively. Distinction was made between three categories of individuals with respect to their patterns of life. An estimate was made of the influence of the terrestrial component of the natural background and of some typical building materials on the indoor radiation level. An average indoor exposure rate of 9.5 muR . h-1 and a dose rate of 95 nGy . h-1 for individuals were found, both with a standard deviation of 15-20%.