On Wed, 20 Oct 1999, Spike Jones wrote:
> > On Tue, 19 Oct 1999, Spike Jones wrote:
> > ...
> > > greenhouse, in which we grow food which is free of carbon 14. If one
> > > eats only food from this greenhouse, one should be able to reduce
> > > substantially the amount of carbon 14 in ones system. Right? spike
> > Robert J. Bradbury wrote: I believe you're approach would work.
> > However I think that most
> > of our internal radiation exposure comes from K40, not C14....
> > ...So while it is an interesting idea, I think we would have to sit down
> > with our caculators and figure out how much this really buys us. Robert
> I chose controlling C14 because carbon is in the DNA. If a carbon atom
> transforms into a nitrogen, it wrecks that strand. Seems like the potassium
> decays would be relatively harmless.
A very good point. The decay of a carbon atom *in* the DNA could have a much greater effect than a K40 atom nearby releasing a large amount of ionizing radiation (since most of the ionization effect is absorbed by the water molecules). However if the K40 abundance or "ionizing potential" can can produce more mutations than the average C14 abundance, then it is the more dangerous element.
> Now that I recall, someone did some calcs on this about a year ago,
> but I do not remember how they figured it would not be a problem. spike
It depends entirely on the abundance of C14 in the DNA vs. the abundance of ionization effects from solvated K40 (or other radioactive isotopes) compared with their half lives and ionizing potentials (and distances from "critical" targets). This isn't a simple equation.
However, my general impression is that in the "real world" the carcinogenesis effects are something like:
plutonium >> radium >> radon > K40 > C14
So I suspect this balances out in terms of the doses and "radioactive efficacy" of the atoms one is typically exposed to. But to really discuss it we need hard numbers.