Why do some unexpected isotopes occur naturally?

1. Jan 25, 2013

holly56

Why do some isotopes occur naturally even though a seemingly valid decay with non-negligible energy release ~Mev, could energetically happen? E.g. Cadmium-106 could decay to Palladium-106 but it is still NATURALLY occuring?

2. Jan 25, 2013

fzero

3. Jan 26, 2013

holly56

Thanks - is this because there is a difference in the orbital angular momentum of the parent and daughter nuclei? I know it HAS a really long half-life, but I don't know how to prove that to myself - what are it's features that result in this?

4. Jan 26, 2013

Bill_K

Cd-106 is, for all intents and purposes, stable. The quoted half-life of >1020y is only a lower limit. Decay to the next element Ag-106 is not energetically allowed, and a hypothetical decay to Pd-106 would require a double beta decay.

5. Jan 27, 2013

snorkack

NO. The LOWER BOUND of the half-life is $10^{20}$ years. There is NO half-life, because there is no upper bound of half-life.

6. Jan 27, 2013

Staff: Mentor

In theory, all those isotopes (including all with at least 42 protons) should be unstable, but their lifetimes are so long that those decays were not observed yet.

As an example, 209Bi was in this list, too, until its radioactivity was discovered (with a half-life of ~2*1019 years).

7. Jan 27, 2013

snorkack

Which isotope is alleged to have been observed to undergo double electron capture?