MEASUREMENTS OF NATURAL RADIOACTIVITY IN GREEK BUILDING MATERIALS

Radon in indoor air is partly due to its exhalation from building materials. It is therefore important to develop techniques for measuring the exhalation rates from such materials and also from their structural modules, such as test walls and concrete slabs. These techniques could be also employed for estimating the remediating effect of coatings used as radon barriers on walls, floors and ceilings. For this purpose an air-tight, N2 filled, 1m³ steel container has been constructed, in which raw building materials and prototype structural modules of volume not exceeding 100 L are enclosed for evaluating their exhalation rate. The environment is conditioned by a heating unit, a humidifier and an air blower, in order to control temperature and humidity over the range 12-45 °C and 15-99% respectively; an aerosol generating system is used to produce particles. The container is equipped with several monitoring transducers on line to data acquisition computers. Radon progeny radiation is continuously monitored in-situ via a 2x2'' Am-doped NaI detector stabilised for spectrum shifts. Several port holes located on the upper and side walls, allow for grab sampling of the radon progeny on high efficiency filters by pumping approximately 15% of the enclosed N2 through the container using accurate flowrate control. The filters are then analysed using high-resolution gamma and alpha spectrographic techniques. The container is calibrated with a Ra-226 source of a nominal activity of 102.8 kBq, shielded in a small metal drum with a lid which can be remotely opened or closed. Concentration of the homogeneously distributed radon can be regulated up to 100 kBq/m³ by appropriately closing or opening the drum. The efficiency of the container has been experimentally determined ranging within 5-30% depending on the environmental conditions inside it.