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).

Measurements performed in Goiânia after a new intervention action in 2001.

Brazil's worst radiological accident took place in 1987, in the city of Goiânia. In 1999 and 2000, detailed measurements of 137Cs contamination were performed in junkyard II, one of the places involved in the accident. High values of 137Cs activity per unit mass were found in soil layers at depths between 10 and 40 cm from the surface, reaching values as high as 175 kBq x kg(-1). High values of 137Cs concentration in fruits and plants were also observed. Moreover, values of ambient dose equivalent rate at 1 m above the ground were found to be higher than the limit of 1.0 microSv x h(-1) set by the Brazilian National Nuclear Energy Commission (CNEN) in 1987. In February 2000, the CNEN was informed about the results of our measurements. As consequence, in August 2001, the CNEN performed a new intervention action in the area, covering all its extension with a concrete layer and removing some plants and trees. The new remedial action reduced the dose rate to approximately 13% of the value prior to covering the site in concrete, reaching values below the CNEN limit, as demonstrated by the measurements presented here.