Aaron Boyden wrote:
}
} "Bruce A. Perreault - Magistrate" wrote:
} > When these depleted shells explode they release particles less
} > than 5 microns in size into the atmosphere! What do you think
} > these minute radioactive particles do once they are breathed
} > into the body?
}
} Based on the best current information about the effects of low levels
} of radiation, the answer is virtually nothing.
>
>Uh. Not cause cancer?
The answer did not say that, it said _virtually_ none.
That answer is correct.
The reason is that DU is primarily 238U (having been "depleted" of most, but not all, of the somewhat shorter-lived 235U isotope that is used as a nuclear explosive), and the lifetime of 238U is a mere 4.468 x 10^{9} years. Materials with billion year lifetimes do not pose a major health risk. You live with that risk every day from a wide variety of naturally occuring radioactive materials.
The radiological risk is proprotional to the specific activity (decays per second per unit mass) of whatever you are looking at, which is inversely related to the lifetime, and the kind of particle released in the decay (alphas being the worst in the body). That is, longer lifetime, less risk, other things being equal.
The risk of an alpha emitter like 238U is much greater than that of a beta emitter such as 40K with 'only' a 1.25 x 10^{9} year lifetime, but more 40K atoms decay in any given time period and there are more atoms in a given mass. Taken together, this means a given mass of 238U (which has 6 times fewer atoms and 3 times less activity but has 20 times the risk) is about the same as a given mass of 40K. Note that 40K is also naturally occuring and, since it is potassium, makes up part of your body at all times. You are probably buying into the concept that any radioactive material (such as your body, what with its 40K and 14C) is inherently dangerous. Those natural sources of radioactivity have a low risk because our bodies evolved mechanisms that repair most minor damage from radiation and other insults our cells put up with. You need exposures many times the natural level before risk becomes detectable in a population.
You might also be jumping to an unwarranted analogy to the risk of inhaling small amounts of plutonium. By comparison, the lifetime of 239Pu (used in nuclear weapons) is only 24,000 years and the lifetime of 238Pu (used in RTGs) is only 87.7 years. The former is 4.468x10^{9}/24,000 = 186,000 times more dangerous than 238U. That is, you would need to inhale about 200,000 of those micron sized dust particles to equal the effect of one from 239Pu. Note that some tons of 239Pu were vaporized during atmospheric testing....
...People who are out to scare you rarely present all of the facts.