Why do some unexpected isotopes occur naturally?

[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 occurring?

 

[fzero]

According to http://www.nndc.bnl.gov/nudat2/reCenter.jsp?z=48&n=58, the half-life of ¹⁰⁶Cd is $10^{20}$ years. The universe itself is only $10^{10}$ years old, so an isotope like this would not have had time to significantly decay.

 

[holly56]

According to http://www.nndc.bnl.gov/nudat2/reCenter.jsp?z=48&n=58, the half-life of ¹⁰⁶Cd is $10^{20}$ years. The universe itself is only $10^{10}$ years old, so an isotope like this would not have had time to significantly decay.

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?

 

[Bill_K]

Cadmium-106 could decay to Palladium-106 but it is still NATURALLY occurring?

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.

 

[snorkack]

According to http://www.nndc.bnl.gov/nudat2/reCenter.jsp?z=48&n=58, the half-life of ¹⁰⁶Cd is $10^{20}$ years.

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.

 

[mfb]

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).

 

[snorkack]

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