Re: Radioactive decay and long-term preservation

Jeff Davis (
Thu, 21 Oct 1999 12:58:00 -0700

Spike wrote:

>I encourage the laughter Jeff. {8^D But I dont get it. Are you saying
>is carbon 14 in coal? I meant, wood has carbon 14 to start with, then
>over the eons it takes to form coal, yer 14 goes away, half every 6k years.

Right you are spike. My mistake in thinking you meant it was *all* gone, as in none, zero, zippo, nada. The not-much-more-than-infinitesimal bit that's left is what is used for carbon 14 dating.

Robert Bradbury wrote:

> I think that most
>of our internal radiation exposure comes from K40

I think Robert may be right. Potassium comprises 0.4 % of the body. That's 272 gms. (statistical average?) Of which 0.0118 % is K40, with a half life of 1.28 billion years. So in 200 years, 0.00000035 gms of K40 will decay (0.00000087 gms in 500 yrs). The predominant decay mode is beta decay (99.99%), with energies (as best I could determine from the SMI periodic table software I used to get these numbers) for the event of 1.312 Mev for the *beta disintegration*, 1.46 Mev gamma emission, and 1.33 Mev *other radiation*.

Perhaps someone else can translate this into rads or some other useful metric of overall radiation damage.

Best, Jeff Davis

	   "Everything's hard till you know how to do it."
					Ray Charles