Accurate measurements of the radon flux of real building materials in existing houses with normalor contaminated walls and/or the mean emanation rate of soil samples, raw materials or building materials are very important for certain studies relating to radon in houses. The two potential sources of errors are that (1). The emanation rate of the disaggregated soil samples (raw materials, building materials), used in the emanation rate procedure outlined below, may be different from the emanation rate under natural setting conditions and (2).

Epidemiological evidence of lung cancer risk from radon is based mainly on studies of menemployed underground in mines where exposures are relatively high in comparison to indoorexposure. Nevertheless direct evidence of risk from residential radon is desirable. In 1990, a studywas started comprising 12 000 inhabitants of an area with elevated radon concentrations. The meanlevel in the houses was higher than general mean of the country by factor of five. In the period1961-95, a total of 173 lung cancers were observed.

Passive radon(222Rn) detectors are commonly used for radon surveys. They provide the integrated exposure. Solid-state nuclear track detectors (SSNTD) are widely used as the detecting material.Usually, determination of radon concentrations is based on the number of tracks produced by alpha particles (track density). In order to obtain the relationship between the track density and the radon concentration (conversion factor: CF) calibration is necessary. The detectors are calibrated in a pure radon atmosphere with a standard radon chamber.

The definition of radon prone area based on indoor radon survey and the statistical analysis of data (ICRP65) is a well known process. Such a definition of radon area involve all parameters that influence radon concentration in dwellings (geology, building technology, user habits, ventilation, etc.) and is useful especially for planing targeted Rn survey and remedial measures in existing houses. However, from the point of Rn protection of new modern buildings, the approach based on "Rnpotential" (geological parameters) seems to be more useful for delineation of radon area.

Raised radon gas levels are known to exist in mines and Show Caves, and in the United Kingdomthe Ionising Radiations Regulations 1985 require the employer to take action to reduce radonlevels by improving ventilation or restricting access, because significant radiation doses can bereceived by workers.In the Mendip Hills, where the underlying rock gives rise to raised radon levels in domesticdwellings, there are a number of cave systems with unrestricted access to recreational cavers;including youth groups.

Radon gas is now considered to be a health hazard when found in excessive amounts in the builtenvironment. The levels of radon vary greatly, with some geographical areas having very highlevels. In the United Kingdom, Northamptonshire was declared an Affected Area in 1992, and itwas at this stage that our group first started studying radon levels and the steps taken to reducethem.The radon levels both before and after remediation were studied, together with the number ofoccupants of affected rooms, and their pattern of occupation.

To evaluate the dose arising from exposure to Rn Decay Products (RDP) a term often used isunattached fraction defined as the ratio of the Equilibrium Equivalent Concentration (EEC) arising from unattached radon decay products (URDP) to the total decay products, that is fu=EECu/EECt. This term is important because the large portion of the dose to the bronchial tissue per unit of inhaled activity is thought to arise due to inhalation and deposition of the URDP.

The indoor radon program in the US. started in the early 1970's in response to CongressionalHearings that recommended the initiation of radon measurements in certain parts of the united Stateswhere enhanced radon caused by contaminated uranium and radium tailings was suspect. In the mid1970's, the Department of Energy (DOE), Environmental Measurements Laboratory (EML),conducted the first indoor radon survey in the New York City Metropolitan area. The two year studyrecommended that radon surveys should be expanded throughout the US.

A newly built radon calibration test bench called BACCARA is presented. A method of calibrationusing a secondary 222Rn standard is described and examples of calibration are given. With thismethod, no reference instrument is needed and one obtains a more accurate determination of the222Rn volume activity.

The Austrian Radon Project (ARP) is aimed to investigate and measure systematically the indoorradon concentration in about 0.5% of all Austrian homes. With the information from this surveyareas of enhanced indoor radon concentration can be identified and people living in such areasshould be encouraged to mitigate their homes. The radon potential is introduced by normalizingthe observed radon data to a standard situation. By mapping the radon potential an overview on thegeological risk for enhanced indoor radon concentrations will be available.