Freethought & Rationalism Archive

SULPHUR · 04-25-2003, 04:19 AM

Which were.

beausoleil · 04-25-2003, 07:24 PM

Quote:

Originally posted by Tim Thompson
[B]K-40 decays to Ar-40 by electron capture. That means one of the bottom electrons gets close enough to the nucleus to get absorbed by a neutron, and bumping the element up to Ar. The half life for this is 1.277 billion years. In principle, this decay rate can be changed by any outside effect that alters the wave function of the electrons at the bottom of the cloud; chemical environment or extreme pressure. This has been observed in Be-7, which also decays by electron capture, and the change in half life is on the order of 0.2%. K-40 has more electrons, so it's harder to bother the ones at the bottom. No similar effect has been recorded for K-40, though curiously Zr-89 and Sr-85 have shown similar, ~0.2% effects.

I don't usually think about the physics of the decay, so please bear with me! The change in K-40 might be hard to detect because the half life is so much longer - I'm not sure the K-40 half life is even known to 0.2%. But isn't it a little more complicated still because most K-40 beta decays to Ca-40. (the branching ration is about 90% beta to 10% EC, if I remember), If so 0.2% change in EC probability is about a 0.02% change in half life, all other things being equal. The build up of Ar-40 would change by 0.2%. however - how do they set about the measurement?.

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04-25-2003, 04:19 AM	#31
SULPHUR Senior Member Join Date: Nov 2002 Location: hobart,tasmania Posts: 551	Which were.

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