Template talk:NUBASE2020

Note on stable nuclides

The total number of nuclides classified as stable in NUBASE is 254. However, three of these nuclides—⁷⁸Kr, ¹²⁴Xe, and ¹³⁰Ba—have been observed to undergo double electron capture, all prior to 2020. As such, to the best of my knowledge at the time of writing, there are 251 (observationally) stable nuclides not known to decay, i.e. observationally stable. ^Complex/_Rational 23:01, 22 November 2022 (UTC)

So, you are doubting NUBASE2020? esp does "prior to 2020" would suggest that they made a mistake or error? And, is the "(observationally)" a clue or irrelevant? Bracketing a defining word is not clarifying imo. I think that word needs its scientific base/clarification at enwiki anyway. DePiep (talk) 07:03, 23 November 2022 (UTC)

"Observationally" just means that those 251 have never been observed to decay. The word is just there because some of them are expected to decay and some of these decays have been looked for.

I agree with CR; we have reliable sources that ⁷⁸Kr, ¹²⁴Xe, and ¹³⁰Ba do decay, so we should reflect that. I wonder if the reason why NUBASE2020 doesn't have them is because these are the only known nuclides with double-EC as a decay mode? Double sharp (talk) 11:30, 23 November 2022 (UTC)

It is not about that I would not know or understand "observationally". I say that if it is relevant, it should be added rationally at appropriate places. For example, in the wording of Ds. (Do the big tables need a standardised footnote option for this?) DePiep (talk) 13:09, 23 November 2022 (UTC)

We have such a footnote, for example in isotopes of platinum: we write "Observationally Stable" for the concerned isotopes (¹⁹²Pt, ¹⁹⁴Pt, ¹⁹⁵Pt, ¹⁹⁶Pt, ¹⁹⁸Pt), and have a footnote saying that the nuclide is believed to undergo decay to something else, with a lower bound on the half-life where it exists. Double sharp (talk) 16:30, 23 November 2022 (UTC)

OK then, OP answered (with Observationally Stable). My questions clear (unbracket Obsv.St.!), so I'll leave this thread unless I get a question. DePiep (talk) 17:11, 23 November 2022 (UTC)

oops, except this: is clear for editors when to use "Stable" or "Observationally stable" per isotope? Is HL the indicator? DePiep (talk) 17:14, 23 November 2022 (UTC)

The distinguishing factor for "observationally stable" is whether such a decay is energetically possible. For instance, ²⁰⁷Pb has a mass of 206.9759 Da, and is theorized to undergo alpha decay to ²⁰³Hg; the products have a combined mass of 206.9755 Da and the balance of 0.0004 Da is liberated as energy—the alpha particle's kinetic energy—implying that this reaction can theoretically occur. However, the energy released (Q-value) is so low that the theoretical half-life exceeds the age of the universe by many orders of magnitude; this decay has a predicted half-life of 10¹⁵² years! As such, ²⁰⁷Pb is observationally stable because its decay can occur, but for all practical purposes it may be treated as stable.

Very rare and probably unobservable decays, however, are important to distinguish from decays that are energetically impossible, i.e. energy is required to induce a decay rather than released from the decay. As an example, ¹⁶O has a mass of 15.9949 Da, whereas ¹²C + ⁴He have a combined mass of 16.0026 Da, which means the energy equivalent of the remaining 0.0077 Da must come from outside the system and so the alpha decay of ¹⁶O to ¹²C is absolutely forbidden, i.e., ¹⁶O is absolutely stable rather than observationally stable. Indeed, fusion of ¹²C + ⁴He is energetically favorable, and so is the reaction by which stars produce oxygen.

I hope this explanation serves as a clear reference. ^Complex/_Rational 17:55, 23 November 2022 (UTC)

Or to phrase it very pithily: (1) a stable nuclide cannot even theoretically decay; (2) an observationally stable one theoretically can, but no one has seen it doing that. Probably the most obvious example of (2) is "too fast to die" ^180mTa. Of course "theoretically" is limited to known physics. (If protons do decay, then there are no absolutely stable nuclides.) Double sharp (talk) 18:30, 23 November 2022 (UTC)

Thanks you both. I wanted to note that this is article-worthy material, not talkpage-help IMO. (I was not going to edit isotopes with this anyway). Please check out (& improve?) target Observationally stable. More so because it deviates from/adds to NUBASE2020 if I am correct. DePiep (talk) 09:43, 24 November 2022 (UTC)

That link seems accurate enough to me. Certainly it could be further expanded, but what it says now is correct. Double sharp (talk) 10:49, 24 November 2022 (UTC)

References

^Complex/_Rational 23:01, 22 November 2022 (UTC)