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.

Radon-reduction in private and public buildings is a current issue. Research has opened our eyes for the enormous fluctuation of the indoor radon level over longer observation periods. Normally, the time sequence of the radon concentration can be characterized as a mixture of (periodic) circadian variations overlayed with (aperiodic) seasonal fluctuations. Other factors may be attributed to the activities of the inhabitants. Today, different expert groups are proposing mathematical models to describe the radon level in a building.

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.

This paper present the results of a test programme to validate the Dutch pre-normative protocol NVN 5623 ‘Radioactivity measurements: Determination of the activity of gamma-ray emitting nuclides in a counting sample by means of semi-conductor gamma-spectr

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.

In the indoor environment short-lived radon decay products deposit onto surfaces. Alpha decaying atoms obtain recoil energy enough to implant into the substrate. This hideaway phenomenon permits the use of implanted long-lived radon decay products as a measure of past radon exposures. Specifically flat glass surfaces has been used as radon retrospective monitors and thanks to the development of special track-etch devices (retro detectors) the implanted surface activity can be measured in-situ.

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.

Measurements of 210Po embedded in glass have been performed with passive detectors in houses ofthree rural communities of Yugoslavia. Field work has been initiated and carried out by the VincaInstitute, Belgrade and analyses have been conducted by SSI (Sweden), UCD (Ireland), NRPA(Norway) and CRR (Italy). Based on 210Po concentration assessments, radon retrospective estimateshave been produced. Fairly good agreement amongst laboratories resulted both for polonium andradon determinations.