While the theft of a truck carrying radioactive cobalt made international headlines, this was unfortunately not the first time thieves or scavengers have exposed themselves or others to lethal radiation. Probably the most infamous case was on September 13, 1987 in Goiania, Brazil. Scavengers broke into an abandoned medical clinic and stole a disused teletherapy machine. These machines are used to treat cancer by irradiating tumors with gamma radiation typically emitted by either cobalt-60 or cesium-137. In the Goiania case, the gamma-emitting radioisotope was cesium-137 in the chemical form of cesium chloride, which is a salt-like substance. When the scavengers broke open the protective seal of the radioactive source, they saw a blue glowing powder: cesium chloride. This material did not require a “dirty bomb” to disperse it. Because of the easily dispersible salt-like nature of the substance, it spread throughout blocks of the city and contaminated about 250 people. Four people died form radiation sickness by ingesting just milligrams of the substance.
The effects could have been worse, but an extensive cleanup effort, costing tens of millions of dollars, captured about 1200 Curies of the estimated 1350 Curies of radioactivity in the disused teletherapy source. To put this Curie content in perspective, a source with 100 or more Curies of gamma-emitting radioactive material would be considered a source of security concern. The International Atomic Energy Agency has published an authoritative account of the Goiania event.
For an in-depth assessment of the radioisotopes of security concern and the commercial radioactive source industry, see the January 2003 report “Commercial Radioactive Sources: Surveying the Security Risks,” by myself, Tahseen Kazi, and Judith Perrera. In that report, we underscore that even suicidal terrorists would have to live long enough to withstand the lethal radiation of a highly radioactive substance to use it as a radiological weapon. Of course, if the terrorists or thieves have training in safely handling radioactive materials, then they would not kill themselves in the process of accessing the material and making it into a weapon.
Based on the news accounts of the recent theft in Mexico, the thieves broke open the box carrying the radioactive cobalt sources and exposed themselves to lethal radiation. They were thus unlikely to have been skilled at handling radioactive materials or even apparently knowledgeable about the cargo they had stolen.
We were lucky this time. The cobalt-60 was reportedly from an old teletherapy machine. While the Curie content has not been reported, I would estimate that it could range from a few hundred Curies to a few thousand depending on the age of the cobalt source. Cobalt-60 has a half-life of 5.27 years, so after that amount of time has elapsed, only half the original amount of radioactivity is left. After two half-lives or about 10.5 years have elapsed, one-fourth of the radioactivity remains; three half-lives, one-eighth and so on. A fresh cobalt-60 source for a teletherapy machine could contain upwards of ten thousand Curies.
While the thieves who exposed themselves will likely die within the next few days from radiation sickness, they fortunately did not expose innocent people. Because cobalt is a solid metal, it is hard to disperse, even with explosives. But if the radioactive material had been cesium-137 in chloride form, this event in Mexico could have been a ghastly replay of the 1987 event in Goiania.
In 2008, the Committee on Radiation Source Use and Replacement of the U.S. National Research Council drew attention to the dangers of cesium chloride. In the report, published by the National Academies Press, the committee ranked cesium chloride as their number one security concern and recommended that the U.S. government take steps to replace the use of this material. Technologies that don’t use radioactive cesium such as X-ray irradiators, for example, are one potentially promising pathways to reduce the use of cesium chloride. The 2008 report discusses incentives to encourage greater development and use of alternative and replacement technologies.
Last year, I wrote a report on “Ensuring the Security of Radioactive Sources: National and Global Responsibilities,” for the 2012 Nuclear Security Summit in Seoul, South Korea. Among the recommendations, I discuss the need for more effective means of tracking shipments, training of response forces, developing replacement technologies for phasing out dispersible sources, and increasing government cooperation in sharing intelligence information about threats to radioactive materials of security concern.
Unfortunately, hijacking of trucks is common in Mexico, but the police were able to track down the truck and the sources were recovered. Without better controls on highly radioactive sources, the next time something like this happens it could be a lot worse.