Thursday, July 22, 2010

If Found ... (a scary and sad story)

The Goiânia accident was a radioactive contamination accident in central Brazil that killed 4, injured 28, and produced over 200 cases of detectable radiation poisoning. On 13 September 1987, an old nuclear medicine source was scavenged from an abandoned hospital in Goiânia, the capital of the central Brazilian state of Goiás. It was subsequently handled by many people, resulting in four deaths and serious radioactive contamination of 249 other people. Time magazine has identified the accident as one of the world's "worst nuclear disasters".

The object was a small, highly radioactive thimble of caesium chloride (a caesium salt made with a radioisotope, caesium-137) 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.

Goiânia’s Instituto Goiano de Radioterapia (IGR), located 1 km northwest of Praça Cívica, was abandoned in 1985. A caesium-137 based teletherapy unit was left behind. Over the following years, many homeless, squatters and scavengers entered the building. Eventually, on 13 September 1987, two men — Roberto dos Santos Alves and Wagner Mota Pereira — came across the radioactive teletherapy head and took it with them in a wheelbarrow to dos Santos Alves's house about 0.6 km north of the clinic. There they partly dismantled the equipment, taking the billiard ball-sized cesium capsule out of the protective rotating head. The gamma radiation emitted by the capsule's iridium window made the men nauseous after a couple of days, but they assumed it was due to something they ate. The exposure eventually caused localized burns to their bodies and one later had to have an arm amputated.

The two men attempted to open the cesium capsule, but failed. A few days later, however, one man did break open the iridium window which allowed him 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 in 1988 at Oak Ridge National Laboratory during the disencapsulation of a 137Cs source.) The man scooped out some of the radioactive cesium and tried to light it, thinking it was gunpowder, and eventually gave up.

On September 18 Roberto dos Santos Alves and Wagner Mota Pereira sold the items to a nearby scrapyard. That night the owner, Devair Alves Ferreira, went in the garage and saw the blue glow from the cesium capsule. Over the next three days he invited friends and family to view the strange glowing substance. Ferreira intended to make a ring for his wife, Gabriela Maria Ferreira, out of the material.

Several people who visited the home came into contact with the dust and spread it around the local neighborhood and to other towns nearby. Ferreira's ownership led to many people becoming contaminated. Another brother of the scrapyard owner used the dust to paint a blue cross on his abdomen. He also contaminated the animals at his farm, several of which died. At this scrapyard, a friend of Ferreira's (given as EF1 in the IAEA report) hammered open the lead casing. On 25 September 1987, Devair Alves Ferreira sold the scrap metal to another scrapyard. He survived the incident.

Ivo, Devair's brother, scraped dust out of the source, taking it to his house a short distance away. There he spread some of it on the floor. His 6-year-old daughter, Leide das Neves Ferreira, later ate while sitting on the floor, absorbing some of the radioactive material (1.0 GBq, total dose 6.0 Gy). She was also fascinated by the blue glow of the powder, applied it to her body and showed it off to her mother.

Gabriela Maria Ferreira was the first to notice that many people around her had become severely sick all at the same time, and her actions from that point on probably saved lives. She first suspected the culprit was a beverage they had shared, but an analysis of the juice showed nothing untoward. On 28 September 1987 (15 days after the item was found) Gabriela went with one of her scrapyard employees to the scrapyard then in possession of the materials. She reclaimed them and transported them by bus in a plastic bag to a hospital. There, physician Paulo Roberto Monteiro 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. Gabriela Ferreira died on 23 October 1987.

A model of the bus cabin was subsequently recreated, 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 2.7 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.

In the morning of 29 September 1987 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.

1 comment:

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