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Cobalt-60 theft in Mexico

Dear Reader,

It has come to my attention that a truck containing a radioactive cargo from a hospital (A used cancer treatment unit) was stolen recently in Mexico. You will be glad to know that the radioactive cargo has been found. A short comment on the case (made at an early time) by the IAEA can be seen here.

Currently it is unknown why the truck and the radioactive cargo was stolen. I do not know if it was a simple truck theft where they wanted the truck, a scrap metal theft or something more sinister such the theft of radioactivity by someone with the intention of causing harm with it (dirty bombers ?).

I hope when I get some time soon to be able to comment further on this case and on cobalt-60 in general. One report claims that circa 3000 curies of cobalt-60 was inside the machine when it was stolen. From my own personal experience I can tell you that this is a large amount of radioactivity, I would expect that the outside of the shielding could feel warm if that amount of radioactivity is inside. The warmth is due to heat being created in the shielding by the absorption of the beta and gamma rays from the cobalt-60, this heat production (decay heat) is perfectly normal.

We can do some fun calculations with decay heat, but I want to save those for later.

The problem with radioactivity units is that two units for activity exist, the old one (curie) was defined as the amount of radioactivity which is equal in terms of decays per unit time as one gram of radium-226. This is a very large amount of radioactivity, one curie is 37,000,000,000 radioactive decay events per second. Or as I would write it 37 x 109 events per second. On the other hand the modern (SI) unit for radioactivity is the Becquerel which is named after the discoverer of radioactivity. This is defined as one radioactive event per second.

The problem with the  Becquerel is that it is very small and for most applications, event things like expressing how much natural radioactivity is in a person, a kilo of earth from my garden [As far as I know there has never been a radioactive soil contamination problem in the town where I live in Sweden] or a packet of coffee) you need to write a large number.

The great problem I see with the curie and the  Becquerel is that both units are very different to each other in size, the  Becquerel can be thought of being like expressing the weight of a car in grams while the curie can be thought of as like expressing the weight of my dog in terms of equivalents of blue whales.


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