Goiânia: 12 years after the 137Cs radiological accident.

In 1987, in the city of Goiânia, Brazil, occurred one of the worst radiological accidents ever reported. The remains of 137Cs contamination in a terrain where part of a radiotherapy unit had been manipulated in 1987 were measured in 1999-2000, and some of the results are presented here. Using the technique of gamma ray spectrometry in situ and in the laboratory, the ambient dose equivalent rate at 1 m above the ground and 137Cs concentration in soil were determined. Values higher than the ones established by the Brazilian National Nuclear Energy Commission (CNEN) as action levels in 1987, namely 0.8 microGy x h and 22.5 kBq x kg(-1), were obtained in that terrain. The 137Cs distribution profile in the soil shows high values of the specific activity in a layer located at a depth of 10-40 cm from the surface, where the soil is mixed with rubble, reaching values as high as 175 kBq x kg(-1).