Radiological survey of Goiânia by a mobile monitoring unit.

In September 1987, a 137Cs teletherapy source was ruptured in Goiânia and environmental consequences ensued. After the initial response to this accident, a radiological survey throughout the city was performed using a mobile unit. This unit was equipped with two Geiger-Müller detectors outside the vehicle and one 102 X 102 mm NaI(Tl) detector connected to a dual recorder. All three detectors were placed 1 m above ground. The survey system covered a wide range of exposure rates, from environmental levels [typically 3.9 X 10(-10) C kg-1 h-1 (15 X 10(-6) R h-1) in Goiânia] up to 2.6 X 10(-3) C kg-1 h-1 (10 R h-1). Eighty percent of the Goiânia urban area was covered by this survey, and except for some specific locations, the contamination was restricted to the main foci surroundings occurring in a nonhomogeneous pattern. The highest value observed in the city after the main foci decontamination was 1.8 X 10(-7) C kg-1 h-1 (0.7 mR h-1) in the 57th Street area where the source was originally opened. The system, designed to perform the survey in the city, played a fundamental role during the decontamination process.