What is the validity of half lives being constant in all radioactive isotopes?

[hunt_mat]

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

 

[Vanadium 50]

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]

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]

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]

The environmental changes are normally miniscule, so it doesn't matter. Electron capture works just fine in K-Ar dating.