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[This is pretty much a copy and paste job from Technetium question but I wanted to add this one in case there was some other explanation] So, I understand that PM doesn't exist in nature [though, I don't know why every reference I see regarding PM says that and then goes on to state that it is found in some stars...] but, if that's the case, then why is it found in some stars? This element doesn't fuse in stars (I think, I found a graph saying that it does) so it has to be left over from supernovae. Lastly, how many stars have been discovered that contain promethium? Thanks much.

Curious Layman
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    You keep posting about elements not existing in nature. All isotopes exist in nature, they just may not exist in large quantities. – CuriousOne Apr 30 '15 at 08:16
  • @CuriousOne AGain, thank you for making the same point I did in the question. Btw, you know technetium gets its name from the Greek 'tekhnetos' meaning artificial? Furthermore, this website says TC is not naturally occurring http://www.rsc.org/periodic-table/element/43/technetium; as does this one: http://education.jlab.org/itselemental/ele043.html And this one says Pm is only artificially created: http://education.jlab.org/itselemental/ele061.html I could go on here but I think I made my point; I thought I made my point in the question. – Curious Layman May 01 '15 at 22:28

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I found this paper discussing the production of promethium in stars. The paper suggests several possibilities:

  • Fission of heavy or superheavy nuclei

  • Spallation of heavy nuclei by high energy protons

  • Reactions of Nd and Sm with low energy nucleons: the s-process

The longest half life of any promethium isotope is 17.7 years, so it isn't going to be left over from supernovae. Promethium has to be produced continuously for it to be present in stars.

John Rennie
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