Shielding of buildings in an urban environment

The shielding of typical buildings, i.e. the reduction of outdoor to indoor exposure due to external radiation, has been measured in 41 Viennese dwellings. Buildings were selected to best represent the building structure of the city by establishing nine different building categories according to different construction periods. The measurements were performed by comparing the gamma flux outdoors to that indoors by in situ gamma spectroscopy and calculational correction for dose build-up. From the measurements the contribution of indoor contamination to indoor exposure was also derived, which ranged from <10% up to 50% of total indoor exposure 8 y after fallout. Immediately after fallout, therefore, possibly significantly higher contributions by indoor contamination may have to be expected. Exposure reduction factors amounted to 0.021 ± 0.006 on the average, old buildings from between the wars and after WW2 showing higher reduction factors of about 0.009, modern prefabricated buildings lower reduction factors of 0.025 and single-family houses displaying the lowest reduction factors of 0.11. Due to the experimental method these factors do not include any exposure reduction due to wash-off and other weathering effects which further decrease the exposure in urban areas as compared to initial fallout levels. (Author)