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The Goiânia accident was an incident of radioactive contamination in central Brazil that killed several people and injured many others. On September 13, 1987, an old radiation source was scavenged from an abandoned hospital in Goiânia, the capital of the central Brazilian state of Goiás. It was subsequently handled by several people and caused serious radioactive contamination, resulting in a number of deaths.
Nature of the source
The object was a small, highly radioactive thimble of cesium chloride (a cesium salt made with a radioisotope of cesium) encased in a shielding canister made of lead and steel with an iridium window. The source was positioned in a container of the wheel type, where the wheel turns inside the casing to move the source between the storage and irradiation positions.
The source contained 74 Terabecquerels (TBq) in 1971. The International Atomic Energy Agency (IAEA) describes the container—51 millimeters (2 inches) in diameter and 48 millimeters (1.8 inches) long—as an “international standard capsule.” The specific activity of the active solid was about 814 TBq·kg-1 of Cesium 137 (half life of 30 years). The dose rate at one meter from the source was 4.56 gray per hour (456 rad·hr−1). It was made in the United States at Oak Ridge National Laboratory and was used as a radiation source for radiation therapy at the Goiânia hospital.
The IAEA document indicates that:
The IAEA states that the source contained 50.9 TBq (1375 Ci) when it was stolen, and that about 44 TBq (1200 Ci, 87%) of radioactivity has been recovered during the clean up operation. This means that 7 TBq remained in the environment; it will have decayed to about 4.4 TBq by 2007.
Theft of the source
When Goiânia’s Instituto Goiano de Radioterapia (IGR) clinic was abandoned in 1985, the cesium capsule was left behind. Over the following years, many squatters and scavengers entered the building. Eventually, on September 13, 1987, two people—Roberto dos Santos and Wagner Mota—came across the radioactive capsule and took it with them in a wheelbarrow. They partly dismantled the equipment, subjecting themselves to external gamma radiation, which caused localized burns to their bodies; one later had to have an arm amputated.
The source is opened
The two men attempted to further open the casing, but failed. They did, however, break the iridium window which allowed them to see the cesium chloride emitting a deep blue light. The exact mechanism by which the light was generated was not known at the time the IAEA report was written. The light is thought to be either fluorescence or Cherenkov radiation associated with the absorption of moisture by the source. Similar blue light was observed at Oak Ridge during the disencapsulation of a 137Cs source in 1988.
The source is sold as scrap
Roberto dos Santos and Wagner Mota sold the object to a junkyard owner—Devair Alves Ferreira (radiation dosage 7.0 Gy, survived)—who intended to make a ring for his wife out of the strange and beautiful blue material.
The sale to the junkyard owner led to many more people becoming contaminated:
The junkyard owner’s wife, Maria Gabriela Ferreira (dosage 5.7 Gy), was the first to notice that many people around her had become severely sick all at the same time. She first suspected the culprit was a beverage they had shared, but an analysis of the juice showed nothing untoward. Her mother came and visited her to nurse her, getting a dose of 4.3 Gy and an intake of 10 MBq (270 µCi).
On September 25, Devair Alves Ferreira sold the scrap metal to another scrapyard.
The source is understood to be dangerous
On September 28 (15 days after the item was found) Maria finally suspected the scrap metal to be the cause. She took the remains of the source by bus in a plastic bag to a hospital, and the physician there rightly suspected that it was dangerous. He placed it in his garden on a chair to increase the distance between himself and the object. Because the remains of the source were kept in a plastic bag, the level of contamination at the hospital was low. The IAEA report suggests that 90% of the radioactivity originally in the source had escaped from it by this point.
A reconstruction of the bus cabin was created at a later time, and it is estimated that a hypothetical passenger who remained in the worst possible location for the entire bus trip (15 minutes) would have suffered a dose of less than 0.3 Sv to the legs. This dose would not cause any injury or acute radiation syndrome. If this hypothetical passenger had been separated by 1.4 meters from the source, then the leg dose would decline to 0.04 Sv. While these prospective leg doses are larger than the normal organ limits for the general public, they are unlikely to cause serious harm in either the short or long term.
The source's radioactivity is detected
In the morning of September 29 a visiting medical physicist (named WF in the IAEA report) used a scintillation counter borrowed from NUCLEBRAS (a national government agency which is involved in the nuclear fuel cycle, including searching for uranium ore) to confirm the presence of radioactivity. The accident response started that evening. Maria, the wife of the scrap metal yard owner, died a month later (23 October) from the effects of the radiation.
The most contaminated people
The outcomes for the 46 most contaminated people are shown in the bar chart below. Several people survived high doses of radiation. This is thought in some cases to be due to the fact that the dose was fractionated. Given time, the body's repair mechanisms will reverse cell damage caused by radiation. If the dose is spread over a long time period these mechanisms can ameliorate the effects of radiation poisoning.
When ingested, radioactive cesium replaces calcium in the bones. The radioactivity then induces cancer in the bone marrow, which then causes leukemia. The following data is too early to show this. In the future, leukemia will affect around 20% of those who ingested the radioactive cesium dust.
Other affected persons
Afterwards, about 100,000 people were examined for radioactive contamination; 244 were found to have significant levels of radioactive material in or on their body. Of this group 129 persons had internal contamination. The majority of the internally contaminated persons only suffered small doses (< 50 mSv, less than a 1 in 400 risk of getting cancer as a result).
1000 persons were identified as having suffered a dose which was greater than one year of background radiation; it is thought that 97% of these people had a dose of between 10 and 200 mSv (between a 1 in 2000 and a 1 in 100 risk of developing cancer as a result).
In light of the deaths caused, the three doctors who had owned and run the hospital were charged with criminal negligence. The main cause of this incident was the severe negligence of the former hospital management who left behind such a dangerous item. The accident demonstrated the importance of keeping an inventory and monitoring of all strong radiation sources by public authorities, which now is legally required in many countries.
Objects and places
Topsoil had to be removed from several sites, and several houses were demolished. All the objects from within those houses were removed and examined. Those which were found to be free of radioactivity were wrapped in plastic bags, while those which were contaminated were either decontaminated or disposed of as waste. In industry, the choice between decontaminating or disposing objects is based only on the economic value of the object and the ease of decontamination. The IAEA recognized in this case, however, that to reduce the psychological impact of the event, greater effort should be taken to clean up items of personal value, such as jewelry and photographs. It is not clear from the IAEA report to what degree this was practiced.
Means and methods
After the houses were emptied, vacuum cleaners were used to remove dust before the surfaces and plumbing were examined for radioactivity. Painted surfaces could be scraped, while floors were treated with acid and Prussian blue mixtures. Roofs were vacuumed and hosed but two houses had to have their roofs removed. The waste from the clean up was moved out of the city to a remote place for storage.
Organic solvents, followed by potassium alum dissolved in hydrochloric acid, were used to treat waxed/greased floors and tables. Sodium hydroxide solutions, also followed by dissolved potassium alum, were used to treat synthetic floors, machines and typewriters.
The clean up operation was much harder for this event than it could have been because the source was opened, and the fact that the active material was water soluble. A sealed source need only be picked up, placed in a lead pot and transported to the radioactive waste storage. In the recovery of lost sources, the IAEA recommends careful planning and using a crane or other device to place shielding (such as pallet of bricks or a concrete block) near the source to protect recovery workers.
Recently, the spread of the contamination in this case has also been used to estimate the effect of a radiological weapon.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Goiânia_accident". A list of authors is available in Wikipedia.|