And now for a quick lesson in radiation physics....

If you have been following the international news lately, You may have heard about the death of Alexander Litvinenko, a Russian dissident. Mr. Litvinenko apparently ingested some polonium-210. Po-210 emits alpha particles. Alpha particles are essentially a helium nucleus: two protons and two neutrons. It's a big, bulky, positively charged charged particle which is relatively slow moving. A sheet of paper or the layer of dead skin cells on your body block them quite readily. Even a few centimeters of air can slow them down dramatically.

However, *if* they get inside of you.....that's altogether different. That big, bumbling tendency makes alpha particles the most destructive form of ionizing radiation. This is the same problem that the radium watch dial painters had. Radium on your watch dial or on your paintbrush isn't a problem, as there is no effective dose of radiation. *Licking* the paintbrush to get a better point on it leads to ingestion of the radium paint. And deposition of an alpha-particle emitting element inside the body where there is no layer of dead skin cells to deflect the particles.

Acute radiation syndrome (the technical name for "radiation sickness") is the result of large radiation exposure in a short amount of time. The damage is chiefly caused by the interference in cell division, thus cells which are rapidly or actively dividing are most susceptible to damage. This is why radiation treatments are used in combating cancer. In the human body, normal tissues which are highly susceptible to radiation damage include bone marrow (source of blood cells), the lining of the gastrointestinal tract and hair follicles. Thus the symptoms of acute radiation exposure include hair loss, massive loss of white blood cells (and correspondingly large increase in infection risk), plus nausea, vomiting and diarrhea. Death can be due to infection or water-electrolyte imbalance. Depending upon the dose of radiation received, death can occur in weeks or in hours. Above 10 Sieverts or 1000 rem, death is inevitable.

Polonium was discovered by Marie and Pierre Curie in 1898. Mme. Curie named it after her homeland, Poland. They discovered it when studying pitchblende. After removing the radium and uranium from the pitchblende, the Curies discovered that the pitchblende was even more radioactive than the uranium and radium combined, leading them to hypothesize that some other radioactive substance was also in there. Polonium has an activity level more than 1000 times greater than radium. Polonium is naturally found in uranium ores (it's part of the uranium decay chain) and has also been found in cigarette smoke made from tobacco fertilized with phosphate-containing fertilizers. (Inhalation is another great way to get this element into the body where it can do large amounts of damage.) Polonium dissolves quite nicely in weak acids, so small amounts could be introduced into food or beverage and used to kill someone. Care for a nice glass of lemonade or a carbonated beverage?

Polonium 210 has a half-life of around 138 days. This means that after 138 days, one half of the original amount of the polonium remains. However, at the end of a second 138 day period, all the polonium is not gone. One quarter of the original amount remains. For each passing half-life period, one half the current amount remains.

So where does one find polonium? In commercial products, it's used in some anti-static brushes for removing dust from photographic films. It's also been used as a heat source in lunar rovers. Certainly exposure risks occur in the mining and processing of uranium ores. Basically the stuff is just too toxic for much commercial use and other compounds are used instead. Ingestion of *micrograms* of polonium-210 is sufficient to result in death due to radiation sickness. Just ~7 x10-12 gram will result in 1100 becquerels as a body burden, which is the maximum limit. You can read more on the health effects of polonium at the Hazardous Substances Data Bank.

However, all of us consume some polonium in our every day diets. Argonne National Lab estimates that the annual US consumption of polonium is around 22 becquerels/year. The only way to keep polonium from getting in to your body is to cease eating, drinking and breathing. If you're reading this blog, it's already too late. You are, in fact, naturally radioactive, but that's a story for later.


Stefaneener said…
Lovely lovely and clear explanation for someone who doesn't follow much usually. But, being in Tennessee, you must have many cringe-worthy pronunciations of scientific terms around you daily! I lived in Knoxville for three years.

Thanks for stopping by my blog -- I have to force Thing 3 to give back the Temple Grandin book ASAP. I'm plowing through the Kathy Reich stuff, too.

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