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From the end of 1996 through March 1999, the spatial and the temporal variability of the soil 222Rnconcentration was investigated at a 20m x 20m test field with porous soil in 0.5 m and 1.0 m depth atnine positions each and at 1m x 1m plots at four positions each. For this, soil gas was collected weeklyinto evacuated scintillation cells and was analysed subsequently for radon activity. In the 20m x 20mfield the spatial variability is characterised by coefficients of variation (C.V.) of 26% at 0.5m, and13% at 1.0 m depth. Within the 1m x 1m plots the C.V. Were 4% and 2%, i.e.

High radon concentrations indoors usually depend on the possibilities of radon penetration from thesurrounding soil into the buildings. Radon concentrations in dwellings up to 100 kBq/m were found insome special regions (i.e. Schneeberg/Saxony, Umhausen/Tyrol) where the soil shows a high uraniumcontent and additionally a fast radon transport in the soil is possible. To reduce the radon exposure ofthe inhabitants in these "radon prone areas" it is necessary to look for building and insulating materialswith low radon permeability.

A study was made of radon-safe building in 300 Finnish low-rise residential buildings using data obtainedfrom a questionnaire study. The study also aims at finding the main defects in design andimplementation and how the guidance given on radon-safe building in slab-on-grade houses has beenfollowed. According to the guidance, the prevention of the flow of radon-bearing air from the soil intothe house is recommended to be carried out through installation of aluminized bitumen felt and use ofelastic sealants.

Experimentally, it has been observed that the radon emanation coefficient, determined for geologicaland construction materials, depends principally on the porosity and water content.

This paper describes the new approach to control radiation exposure from natural sources toinhabitants of dwellings that is presently being considered in the Netherlands. The goal of thisapproach is to uphold the current rather favourable situation (average annual effective dose due toindoor radon and external radiation in dwellings is approximately 1 mSv). To achieve this goal amodel is foreseen to predict the potential effective dose an inhabitant may receive from a dwelling onbasis of its building plan. A scheme to calculate this dose is proposed in this paper.

The Austrian radon mitigation joint research project SARAH (supported by the Austrian Ministry ofEconomy and the Government of Upper Austria), a two-year follow up study of the Austrian NationalRadon Project (NRAP), was started in 1996. Objectives of the research project were to find simple,cost effective experimental methods for the characterisation of the radon situation in dwellings and toevaluate technically and economically the implementation of state of the art remedial actions forAustrian house types.

Implanted long-lived radon decay products in glass surfaces have been used as a measure of pastradon exposure in homes. Special track-etch devices (so-called retro-detectors") attached to the glasssurface, have the ability to specifically measure the implanted activity of 210Po in-situ. Calibratingthese devices for 210Po is fairly straightforward, but the retro-detectors are also sensitive to thebackground activity of the glass substrate.

In recent years, 210Po implanted in glass artefacts has been used as an indicator of the mean radon gasconcentration in dwellings in the past. Glass artefacts have been selected in many dwellings and the?-recoil implanted 210Po concentration has been measured using various techniques. Some of theseretrospective techniques use a model to estimate the retrospective radon gas on the basis of thissurface 210Po activity. The accumulation of 210Po on glass surfaces is determined by the depositionregime over the exposure period.

The identification of a radon-affected area in the south of Yugoslavia was based on geologicalstructuraland geochemical prospecting data of radioactive and other mineral resources. An anomalousarea was recognized at a rural community Gornja Stubla (in the extreme south of Serbia), whileprospecting for uranium in the region on the margin of the large Vardar Zone geotectonic unit.

Investigations on the retrospective estimation of radon exposure in homes had already been carried outin international collaboration in the uranium mining regions of Germany since 1994. Following aConcerted Action named "Retrospectively Estimated Radon in Areas Affected by Uranium MiningActivities " was agreed upon.