Authorities have blocked off an area of 2,000 square yards where they said adults and children, homes, back yards, cars and domestic animals have been exposed to varying doses of radiation.

Government nuclear experts said they had found seven highly contaminated areas and another seven places where radiation was less dangerous. The high-level radioactive waste from 25 homes and from several hospitals where victims of the accident have been treated, the experts said, is being collected and awaiting burial at a designated site in the Amazon basin.

The accident has caused enormous impact here and abroad, not only because of the high number of casualties but also because it has reminded Brazilians of the potential dangers posed by both a large nuclear reactor near Rio de Janeiro that has suffered many failures and by the large array of equipment throughout the country that is loaded with radioactive material.

Cesium 137 is commonly used in the form of powder or pellets to give a radiation dose to cancer patients and also has wide application in industry, for example in gauging the density of welds. Produced in nuclear reactors, it is one of the lethal substances that escaped during the Chernobyl nuclear disaster in the Soviet Union. Began in September

The story, as pieced together by the authorities, began in early September when several young men stole an unused irradiation machine left behind when the privately owned Goiania Institute for Radiology moved. They hauled the heavy piece off to sell it to a scrap metal dealer, Devair Alves Ferreira, 33, in whose back yard it was left.