Ambient dose equivalent rate in Goiânia 12 years after the 137Cs radiological accident.

This paper describes the situation of ambient dose equivalent rates in four of the main foci of 137Cs contamination in the city of Goiânia, Brazil, in 1999, 12 y after one of the worst radiological accidents in the world. During the decontamination, all the buildings of the three highly contaminated sites were demolished and the top soil removed. Afterwards, the soil of two of these lots was covered with concrete, and they remain vacant today. The soil of the third of these lots, identified here as E, previously known as junkyard II, was covered only with clean soil. Three to four years after the accident, new houses were constructed on this lot, and some very poor people live and work there collecting recyclable material. Gamma ray spectrometry, with a portable survey meter, was performed in the quoted places along with outdoor measurements in many other locations of Goiânia. The average ambient dose equivalent rate due to natural background radiation from radionuclides in the soil and cosmic radiation in non-contaminated areas of the city of Goiânia is 62 nSv h(-1). In most of the highly contaminated sites during the accident, the average ambient dose equivalent rate ranged from around 100 to 1,000 nSv h(-1). The only exception was site E, where values of ambient dose equivalent rate as high as 2.6 microSv h(-1) were found.