Measurements of gamma radiation in Swedish houses by means of mailed CaSO4-Dy dosimeters

A nationwide investigation of gamma radiation in Swedish houses has been made. The occupants of 2 000 apartments and houses have been picked out at random and asked to participate. The measurements were made with CaSO4-Dy thermoluminescence dosimeters. Three such detectors were sent to each of the selected dwellings by mail. The detectors were accompanied by instructions in which three different places in the apartment were carefully specified and the participants put the detectors in these places themselves. After a period of four weeks the detectors were returned for evaluation. Desirable detector qualities for this kind of investigation are discussed and some measurements to check the qualities of CaSO4-Dy dosimeters are described, including energy dependence, fading, annealing, sensitivity to light and response to cosmic radiation. The problem of determining the transit dose during mail transport is also discussed. Some preliminary results are shown for four different kinds of building materials. The preliminary mean annual absorbed tissue dose in Sweden is 0.58 mGy (58 mrad) when the contribution from cosmic radiation has been subtracted