Re: Halflife and Randomness

In message <194504265.0000eaea.007.0001@xxxxxxxxxxxxxxx>, TomS <TomS_member@xxxxxxxxxxx> writes

I do have a trivia question (for which I don't know the answer):

There are three basic modes of decay: alpha emission, electron emission, and positron emission/orbital electron capture. (And gamma emission, but this doesn't change the atomic number or atomic mass.)

Is there any nucleus which exhibits all three modes?


There are other decay modes. (Spontaneous fission is the best known one, but there are others, such as double proton decay in Fe-45 and Ar-31.)

To oversimplify, B- decay occurs when there's an excess of neutrons, and B+ decay when there's an excess of protons. So it's going to be rare for an isotope to show both decay modes.

However even-even isotopes are in generally more stable than odd-odd isotopes. Consequently there are some instances in which both modes occur, such as K-40 (19 protons, 21 neutrons) which can decay to either Ca-40 (20, 20) or Ar-40 (18, 22). (Ca-40 apparently decays to Ar-40, by double electron capture, with a half-life of 10^21 years.) In this case alpha-decay to Cl-36 seems not to be possible.

For ground state nuclei you'd be looking for isotopes near the crest of stability, but on the upslope from Fe-56 where alpha-decay is possible.

However there are also excited state of nuclei. These can decay by gamma-emission to the ground state, but can also decay by other decay processes, particularly if the gamma path represents a "forbidden" transition (e.g. if the angular momentum of the two states differs by 2, and the state with intermediate angular momentum has a higher energy than either). It is plausible that a sufficiently excited state of K-40 could decay to Cl-36, but the half-life is probably huge, and the other decay modes much, much, much more frequent.

But, sorry, I can't offer a nucleus which definitely meets the requirements.

Tc-100 and Pm-146 are other isotopes which display both B- and B+ branches.
--
alias Ernest Major

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