Assessment of environmental dosis of ionic radiation in the population of São Paulo, Brazil Elisabeth Yoshimura, Professor of Instituto de Física, Universidade de São Paulo, Brasil. Objectives: - To assess the spatial distribution of environmental dosis of gamma radiation in the city of São Paulo, Brasil. Methods: An investigation was performed to obtain the gamma contribution to the dose received by the population in the city of São Paulo, Brazil. Gamma ray spectroscopy with a sodium iodide scintillator was chosen as the technique, due to the easiness of use, high sensitivity and possibility of detection of an eventual contamination. Measurements were taken at 1 m from the ground, outdoors at the streets, and indoors at commercial places. Besides the gamma spectra, an internal algorithm of the equipment provides the evaluation of the ambient dose equivalent rates. All the maps were prepared using SIGEpi and SPRING (developed by INPE). Results: It was found that the indoor dose rates are, in average, 40% higher than the mean outdoor value. No statistically significant cluster of dose values was found in the distribution of outdoor values over the city territory, although a non-homogeneous pattern is observed. As the indoor sample is concerned, the statistical analysis points to different mean values, according to the category of the commerce.