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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.

Analysis of a comprehensive database containing all available indoor radon measurements which were carried out in Israel between 1989 and 1994 (total of 31,842 assays) coupled with Geographical Information System (GIS) capabilities and geophysical data, shows a significant correlation between indoor radon levels and its levels in the underlying bedrock.

In the last twenty years the interest of the international scientific community on naturally occurring radioactive materials (NORM) in the environment and industry has been ever growing. In particular, the use of gamma-ray spectrometry techniques for activity measurements of gamma emitters belonging to uranium and thorium decay series greatly contributed to these investigations.

A dwelling in M?traderecske in the Hungarian north-east region was selected to study the radon daughter (RD) behaviour in a family room with natural low ventilation under living conditions. The selected house is erected on a geology where a relatively high radon concentration with yearly average of 1KBq/m3 exists. The room is considered a natural radon chamber where the most convenient environmental conditions are. Radon concentration was measured continuously by a monitor (Atmos10, Gammatechnik Sweden and Pylon Electronics of Canada).

Indoor radon concentrations in Athens and neighborhooding areas are relatively low compared withvalues in the northern part of Greece [1,2]. Nevertheless, we have localized a dwelling near Athens(N. Makri), with an elevated radon concentration. We attained this result from the integrative sampling etched track detector placed in open mode (nitrated type film Kodak) for one year long.The etching procedure and estimation of concentration (Bq/m3 with an uncertainty of 20%) wereconducted by the radon facilities of the Institute for Testing and Disaster Medicine, Milin, CzechRepublic [3].

In accordance with the Basic Standards of Radiation Protection issued by EURATOM and the recommendations of the Federal Commission of Radiation Protection (SSK), radon measurements were carried out at 80 of a total of 240 waterworks in the state of Baden-Wrttemberg from the end of 1994 to mid-1997. The measurements covered more than 1000 working places. The waterworks were selected among others on the basis of the number of employees, the size of the supply area, the geological and hydrological parameters, and the surface coverage.

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.

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.

In the Bihor uranium district there are an operating underground mine and the closed down open pit mine. The open pit mine was operated by the Soviets between 1952-1964, the ore being "exported" to the Soviet Union. The mean content of the uranium ore was 2%. The "waste rocks" from the open pit mine were used by the natives in the foundations of detached houses in rural areas. The goal of the survey was to identify this houses and to make radon and gamma dose rate measurements to assess the annual effective doses incured by the public.

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.