ENVIRONMENTAL RADIOACTIVITY IN HIGH BACKGROUND AREAS OF BRAZIL

A geotectonic belt encompassing the archeo-brazilian block in Brazil has numerous foci of intense mineralization closely related to the diastrophic phases of its evolution during the ages. Abundant minerai deposits and a number of hydrothermal spas are located along the belt and in many areas radioactive minerals are associated with the lines of fracture and with the upward diffusion of metallic and metalloidic elements to the surface, resulting in local infiltration or generalized contamination of the strata. Five different types of radioactive ore deposits have been distinguished. Results are reported from a 6000-kilometer field trip through the northern part of the state of Rio de Janeiro, the state of Espirito Santo, and the southern part of the state of Bahia. Measurements were made of the radiation levels. The survey was confined to regions where radiation levels were at least several times the normal background level. The survey was conducted as part of a study of the biological effects of chronic exposure to low levels of ionizing radiation. The geological features of the region are discussed in detail. Measuring instruments and methods are described and results of the survey are presented. (C.H.)