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The horrors of polonium

Dear Reader,

I read recently how it has been suspected that Yasser Arafat may have been murdered using polonium-210. This claim that polonium-210 has been used for another murder made me think for a moment about radium-226 and its daughters. I can tell you that polonium-210 is one of the radioisotopes which most radiation workers love to hate. Polonium-210 and radon-222 are both alpha emitters which are able to diffuse through rubber and plastics. This makes them more mobile than plutonium is. When you write plutonium you have to be careful to understand that not all plutonium is born equal.

Plutonium-239 is a long lived alpha emitter which has a moderate activity per gram (and emits few gamma photons and neutrons), pellets of plutonium dioxide which have been sintered are solids which are clean to handle inside a glove box. I used to work with a nuclear fuel chemist (John Pecket) who used to make plutonium dioxide fuel, MOX and some very werido fuels. He told me how Pu-239 was a nice radioisotope to work with, while plutonium-238 was a nightmare in comparison. Pellets of plutonium-238 dioxide emit so much heat that they tend to glow red hot, they also tend to emit plenty of radioactive dust. He told me that if you place a Pu-238 pellet in a glove box then within days every surface in the box will be crawling with radioactivity. But even plutonium-238 will not pass through a neoprene glove. Thus at least it will stay inside the glove box, the worst radioisotopes I know are alpha emitters which are very mobile.

You can think of low LET radiations (beta / gamma) as being a bit like a goblin with a big stick. This horrible little monster will chase you around the house before trying to hit you with the stick, it can do you some harm but in some ways there is something worse. For alpha imagine a big bath filled with boiling hot jam, while the bath might not be able to chase you, if you fall in then you are going to get a far worse injury. The alpha is very short ranged but if it does get you then it can go a lot more harm than the beta or gamma.

The super mobile alpha emitters are like a evil goblin armed with a steel bucket of boiling hot jam, this evil goblin is also equipped with running shoes or roller blades so it is able to chase you before throwing the boiling hot jam on you. In short this ones combine the some of worst features of alpha and the more long ranged nasties. The only way to stay safe from this wicked goblin is to lock all the windows and doors of the house and keep him sealed outside, with some luck he will die of old age (become weaker when he decays away) before you have to go outside to mow the grass.

OK time to return from analogyland back to reality

With these mobile alpha emitters special extra precautions are needed to keep them contained, for example with polonium-210 some people have been known to put a glove box inside another glove box to increase the thickness of plastic through which the polonium needs to diffuse. Also for radon-222 some people trap the radon on an absorbent material rather than allow it to wander freely around their glove box.

I feel that many members of the general public have a great misunderstanding of what it is like to work with radioactivity.

I have heard of radiochemists being asked “do you glow in the dark”, the short answer is “no”. While the long answer is that is close to impossible to get sufficient contamination on you to make you glow, the only creditable cases I have heard are of some of the radium dial painters who painted their bodies with the radium based glow in the dark paint.

A paper on the legal battle for compensation can be seen here.

I think that the worst aspect of the radium dial industry was the fact that many workers would lick their brush to get a better shape tip. If you look at this document you will see that radium-228 may have been the real villain rather than radium-226. I hold that the pre 1926 two radium dial painting industry could well be the worst part of the radioactivity sector. It is interesting that it appears that only 20 % of the radium which is taken orally is retained in the human body.

Also according to Norris et. al. as cited in this report the human body is quite good at eliminating radium from its self. Some years ago in America as part of a crazy attempt at curing mental patients some people at Elgin state hospital were injected with radium. Using the data from these medical treatments it was possible in the 1950s to work out a mathematical model for the retention of radium in a human. I have rearranged this equation and used a standard bit of maths which allowed me to calculate a biological half life for radium of only 1.33 days.

This value is rather shocking to me, as a chemist I have always been taught and held the view that radium, strontium and lead are calcium mimics which have very long biological half lives because they become part of the bones. I suspect that if radium is injected or swallowed that only part of the radium which enters the blood stream will end up in the bones. While the biological half life of the radium in the bones may be very long, the biological half life of the radium in other parts of the body will be much shorter.

As a result the half life will appear to change if you consider the whole body after a single intake of radium, I suspected that the biological half life will appear to become longer with increasing time after the intake of the radium. Reading more of the report I found that Norris in 1955 published a mathematical equation which predicts how radium is slowly lost from a human. An article in Nature (March 1969, 221, 1059) suggests that the biological half life for radium in humans (long after the intake) is between 10 and 36 years.

The review of radium in humans points out that Dudley in the 1960s suggested an experiment using short lived radiotracers, the experiment was done using humans and it was found that only 20 % of the radium in a mock dial paint was absorbed when it was taken by mouth while only 0.02 % of the thorium in the dial paint was absorbed.

Another interesting point from the review is the fact that if radium-226 sulfate is deposited in the lungs then 25 % of the radon formed can be exhaled, while if radium-226 is deposited in the bones of a person then 60 to 70 % of the radon can be exhaled. This is an interesting difference, which I suspect is due to the difference in the mobility of radon in bone tissue and radium/barium sulfate. I may well get back to this point later.

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