Tuesday, June 7, 2011

Radiation: So Many Experts - So Much Controversy

I spend much more time than I should trying to understand why there is so much disagreement among experts over the subject of radiation. We are bathed in radiation every day of our lives. Some is harmful, some beneficial and some we cannot agree upon. The Three Mile Island incident started my first inquiries into ionizing radiation. The sudden interest in Radon gas prompted another inquiry. Chernobyl brought it to mind again. Now Fukushima has piqued my interest again.

Before Fukushima I just assumed that Plutonium was extremely dangerous. It was the terrorist dream material. It was used to make the big bombs. It was supposed to be the most poisonous of the radioactive elements made by man.

Trying to sort out which experts to believe, I have spent more time studying Plutonium and Radium this time around. It is hard to find an expert opinion that makes sense.

Radium 226 is the most stable of the radium isotopes and is naturally occurring. It is a decay product of Uranium 238, the most common form of Uranium. Radium 226 has a fairly short half life at 1601 years. It decays by releasing an alpha particle into Radon 222 giving off 4871 KeV of energy. Radon 222 has a half life of only 3.8 day and decays by releasing an alpha particle into Polonium 218 with a half life of 3.1 minutes, giving off approximately 5500 KeV of energy, which decays to Lead 214 with a half life of 3.1 minutes giving off an energy of approximately 5000 KeV, which decays by Beta emission to Bismuth 214 which beta decays with a half life of 27 minutes to Polonium 214 with a half life of 20 minutes to Lead 210 with a half life of 160 milliseconds. I'll stop there since Lead 210 has a half life of a full 22 years.

Plutonium 239 decays has a half life of about 24,000 years which decays to Uranium 235 releasing 5245 KeV. Uranium 235 has a half life of 700 million years.

Energy wise, if you consume Radium 226, there is a lot of radiation released within a day or so on the order of 23,000 KeV, after one Radium 226 atom pops. Radium has a pretty significant decay chain with a large biological impact. Still, since it is common in Brazil nuts, it does not seem to be that harmful with tests indicating it is safe in levels up to 1000 times normal background.

Plutonium 239 with about of the quarter of the energy and 15 times less likely to pop than Radium 226 is considered 100 times more dangerous. That does not make sense.

In a reactor, Plutonium 239 produces 207,100 KeV during fission. There should not be a great likelihood of fission in the body, but perhaps this is where the 100 times more dangerous comes from, an unlikely situation. During fallout following a nuclear incident, it is pretty unlikely that large concentrations of Plutonium 239 would end up in an area far from the power plant. That is the case at Fukushima, a few traces were found and only one appears to be confirmed from power plant. The rest appear to be due to atmospheric testing in the fifties and sixties.

The danger from ionizing radiation is the decay frequency and energy per decay. There is some danger from the chemical properties of the heavy metals, but that is unlikely to be the case in food contamination. So Radium 226 should be 4 times more dangerous than Plutonium 239 if ingested.

So this has me really suspicious of some of the anti-nuke experts warning of the dangers of fallout from Fukushima in the US and Canada. That fallout may possibly increase radiation levels by 5 pops per day versus about 25 pops per second from a good thick steak or 15 pops per second from a tofu burger. The source of the ionizing radiation may be different, but it is the energy that counts.

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