The Nuclear Engineering Section of the National Technical University of Athens undertook the organisation of a European building material radon exhalation rate intercomparison exercise in the framework of the European Research into Radon In Construction Concerted Action (ERRICCA). The intercomparison started in June 1998 and it was concluded in February 1999. Twenty participants from 13 countries took part. The exercise focused on the radon exhalation rate determination from a concrete slab, specially constructed to produce radon surface flux well below 10 mBqm-2s-1.

High concentrations of natural radionuclides in building materials result in high dose rate indoorsdue to radon and thoron exhalation and the ?-rays emitted from them. Among the naturalradionuclides contained in building materials, most attention has been given to 226Ra due to 222Rnexhalation and the subsequent internal exposure. In external dose calculations due to buildingmaterials it is usually assumed that there exists radioactive equilibrium among the radionuclides ofboth the uranium and thorium series.

Four commercially available integrated radon concentration measurement instruments, produced by the same manufacturer in the period between 1996 to 1998, have been tested to study the effect of absolute humidity on the radon counting efficiency. All four devices use high efficiency dRAM cells semiconductor sensor chips for alpha particle detection. The chips are located inside a measurement chamber, which is separated from the ambient air by a filter.

The Megalopolis lignite field basin in southern Greece, with Megalopolis-A and B lignite-firedpower plants in operation (total 900 MW), has been repeatedly investigated during the past 25years by the Nuclear Engineering Section of the National Technical University of Athens (NESNTUA).The present work aims at an integrated radioenvironmental approach leading to the doseassessment to the public and to the plants staff.

According to the recommendations of the ICRP and the German Commission on RadiologicalProtection, areas should be identified where increased radon concentrations in buildings occur morefrequently than on the country-wide average. Such regions are characterized by an increased radonpotential of the building ground. The highest indoor concentrations were measured in old houses ofgranitic ground and in mining regions.The identification of such areas in the first step is based on a small-scale investigation of the geogenicradon potential.

^ Department of Experimental Physics, University College Dublin, Dublin 4, IrelandCase-control studies on lung cancer and radon in dwellings have been conducted in North Americaand Europe, including one study in Lazio region, in Central Italy. Great attention is generally devotedto the reduction in the uncertainty in radon exposure assessment because it can give rise to relevantuncertainty in the estimated risk. One of the main potential sources of uncertainty is the use ofcontemporary radon concentration measurements as estimators of past concentration values.

Many retrospective studies regarding the long time exposure to radon (222Rn) are based on theaccumulation of 210Pb (T1/2=22.3y) on the surface of glass objects or other materials and measuring thespecific alpha activity of 210Po (T1/2=138 d, E?=5.3 MeV) resulted by implanting of radon daughters,due to the alpha recoil. In the case of thoron (22oRn) this method is not applicable because there is nota long life time isotope to allow a signifficant accumulation of any descendant. The longest life timeof the thoron descendants is 212Pb with a live time of T1/2= 10.6 hours.

The National Survey on Radon Indoors was designed to estimate the distribution of annual radonconcentration in Italian dwellings, on the basis of a representative sample of about 5000 dwellings. Itstarted in 1989 and ended in 1994, involving all Italian Regions except Sicilia and Calabria, due toorganizational problems in these two regions of Southern Italy. After the official conclusion, tworegional surveys were also carried out in Sicilia and Calabria, using the same experimental apparatusand protocols as in the other Regions.

A first review of the numerous data on the areas in Italy where high radon concentration in dwellingshave been found is presented here. The data were obtained from the national survey and from severallocal surveys carried out in areas where high radon concentration values were expected, on the basis ofthe national survey results or of geological considerations. The analysis is restricted to data obtainedwith long-term measurements.

A nation-wide survey of radon concentrations in Norwegian dwellings was undertaken in the period 1987 - 89. In this survey, radon measurements were made by CR-39 etched track detectors (six months integration time) in the main bedroom of approximately 7500 randomly selected dwellings built before 1980. The annual average radon concentration in Norwegian bedrooms was calculated to 51 Bq/m3, and 3.7 % of the results exceeded 200 Bq/m3.