Radon surveys started in Estonia in 1989. The Department Building Physics at the Estonian BuildingResearch Institute measured radon levels in dwellings, in building materials produced in the country,and in the soil. The indoor radon concentrations in more than 400 houses were measured under grabsamplingtechniques using Lucas cells. The highest measured radon level was 6700 Bqm-3. The resultsof these measurements made during 1989-91 showed that the main source of indoor radon is the soilunderneath buildings.

In Denmark, a new survey of indoor radon-222 has been carried out. One-year alpha trackmeasurements (CR-39) have been done in 3019 single-family houses. There is from 3 to 23 housemeasurements in each of the 275 municipalities. Within each municipality, houses have been selectedrandomly. One important outcome of the survey is the prediction of the fraction of houses in eachmunicipality with an annual average radon concentration above 200 Bqm-3.

Numerical modelling is a powerful tool for studies of soil gas and radon-222 entry into houses. It isthe purpose of this paper to review some main techniques and results. In the past, modelling hasfocused on Darcy flow of soil gas (driven by indoor-outdoor pressure differences) and combineddiffusive and advective transport of radon. Models of different complexity have been used. Thesimpler ones are finite-difference models with one or two spatial dimensions. The more complexmodels allow for full 3D and time dependency.

Radon, radon progeny and unattached radon progeny were measured in two chambers with differentcharacteristics at the Jenolan Caves, New South Wales, Australia, in 1996. Meteorological parametersand condensation nucleus concentrations were measured in order to understand the processesgoverning the radon concentration and degree of disequilibrium with the progeny. One chamber waspoorly ventilated, and rainfall proved to be the most important influence on radon concentration.

Greek Atomic Energy Commission (GAEC) is the regulatory and competent authority on radiation protection matters. In order to facilitate the implementation of the new European BSS Directive, which refers to the Radiation Protection at work places with increased levels of natural radiation exposure, GAEC has upgraded its present infrastructure specifically in the field of dosimetric measurements and monitoring

The very high indoor radon concentrations found in the western part of Switzerland in the early80th were at the origin of an extended research programme between 1987 and 1991. The resultsobtained showed a real need for a further detailed radon programme. This should be based on thestate of knowledge, take economical aspects into account and be practically orientated. The mainaim is to deal with elevated concentrations.

In 1995 and 1996 radon concentrations and effective air flows were measured in about 1500 Dutchdwellings built between 1985 and 1993. The goal of this investigation was to describe the trend inthe average radon concentration by supplementing the first survey on dwellings built up to 1984and to quantify the contributions of the most important sources of radon. In the living room of newdwellings the average radon concentration was 28 Bq m-3, which is 50% higher than in dwellingsbuilt before 1970.

For over ten years STUK (The Radiation and Nuclear Safety Authority, Finland) has performedsystematic indoor radon mapping with municipal health authorities. In the most radon-proneprovinces (Uusimaa, Kymi and Hme) there are about 480,000 low-rise dwellings. It is expectedthat in 51,000 homes the action level of 400 Bq/m3 is exceeded, of which about 6,000 have beendetected. In the rest of Finland the numbers are: 820,000 low-rise dwellings, 17,000 expectedcases of exceeding the limit, of which 800 were detected, respectively.

The relation between an increased risk for lung cancer and exposure to indoor radon is assessed inepidemiological studies. Both the quality and reliability of smoking data and the radon exposuredata are of primary importance. Contemporary measurement of radon concentration in thedwellings of the individuals in a case-control study is traditionally used to assess the past radonhistory. These assessments contain large uncertainties since the contemporary measured radonconcentration might not be representative for the situation a long time ago.

A data set of long-term radon measurements in about 2200 houses in southern Belgium has been collectedin an on-going national Rn survey. The spatial variation of indoor Rn concentrations is modelled byvariograms. A radon distribution map is produced using the lognormal kriging technique. A GIS is usedto digitise, process and integrate a variety of data, including geological maps, Rn concentrationsassociated with house locations and an administrative map etc. It also allows to evaluate the relationshipsbetween various spatial data sets with the goal of producing radon risk maps.