SHIELDING OF BUILDINGS IN AN URBAN-ENVIRONMENT

The shielding of typical buildings, i.e. the reduction of outdoor to i ndoor exposure due to external radiation, has been measured in 41 Vien nese dwellings. Buildings were selected to best represent the building structure of the city by establishing nine different building categor ies 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 in door exposure was also derived, which ranged from <10% up to 50% of to tal indoor exposure 8 y after fallout. Immediately after fallout, ther efore, possibly significantly higher contributions by indoor contamina tion 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 pre fabricated buildings lower reduction factors of 0.025 and single-famil y houses displaying the lowest reduction factors of 0.11. Due to the e xperimental method these factors do not include any exposure reduction due to wash-elf and other weathering effects which further decrease t he exposure in urban areas as compared to initial fallout levels.