Half lives being constant


by hunt_mat
Tags: constant, lives
hunt_mat
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#1
Mar22-12, 06:42 AM
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Hi,

I has talking to someone aboutthe half lives of certain radioactive isotopes not be constant. He cited this paper:
Chih-An Huh, “Dependence of the Decay Rate of 7Be on Chemical Forms,” Earth and Planetary Science Letters 171(1999):325-328

And it seems that they can change, and quite considerably, to within around 1% or so. So my question is, would this be valid for all radioactive isotopes or just certain ones?

Mat
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Vanadium 50
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#2
Mar22-12, 08:04 AM
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Isotopes that decay by electron capture can have their half-lives changed by modifying the electronic configuration. In the extreme case, if you fully ionize a nucleus that decays by capturing an electron, it won't be able to decay.
Vanadium 50
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Mar22-12, 08:06 AM
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To add, Re-187 is unstable against beta decay. Fully ionized Re-187 is stable: the electrons shift the beta energy by about 20 eV, but since the energy is very low (3 eV or so), it moves it from above threshold to below threshold.

hunt_mat
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Mar22-12, 08:12 AM
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Half lives being constant


Interesting. I thought that radioactivity was caused by instability of the nucleus and therefore was based upon probability for the decay.

So if some elements decay via electron capture they're probably not a good one to date things with?

Thanks for the information by the way.
Vanadium 50
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Mar22-12, 11:01 AM
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The environmental changes are normally miniscule, so it doesn't matter. Electron capture works just fine in K-Ar dating.


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