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My favorite isotope story is the detection of tungsten-180's decay. W-180 has a half life of 10^18 years. It was observationally stable, until its theoretical r
by segfaultbuserr 3y ago
My favorite isotope story is the detection of tungsten-180's decay. W-180 has a half life of 10^18 years. It was observationally stable, until its theoretical radioactivity was confirmed in 2009 by Cryogenic Rare Event Search with Superconducting Thermometers - an experiment meant to search for dark matter. Tungsten was used inside the detector, and the sensitivity of the instrument enabled the detection of W-180's alpha decay with confidence [0]. Dark matter was nowhere to be seen, but at least they still got an interesting minor result.
> All naturally occurring tungsten isotopes are expected to alpha decay into hafnium, but with extremely long lifetimes. Since the decay energies for all these decays are in the same energy range as beta and gamma backgrounds from the natural decay chains, their observation is a difficult task. Yet with cryogenic scintillator experiments, these backgrounds can be discriminated from the alpha signal, leading to a basically background free measurement of such alpha decays, see figure 13. Hence, the natural decay of W-180 was observed unambiguously for the first time.
Update: Apparently it was not the only rare decay detected during a dark matter experiment, in fact dark matter searches are a major source of rare decay detection. Previously in 2003, Bismuth-209's radioactivity was also detected as a bonus result of a dark matter search, with a half life of 10^19 years. [1] In 2019, the XENON1T experiment detected the radioactivity of Xenon-124 (again, because Xe was used inside the detector), with a half life of 10^22 years. By far it's the rarest radioactive decay ever directly observed by physicists [2].
[0] https://en.wikipedia.org/wiki/Cryogenic_Rare_Event_Search_with_Superconducting_Thermometers https://en.wikipedia.org/wiki/Cryogenic_Rare_Event_Search_wi...
[1] https://physicsworld.com/a/bismuth-breaks-half-life-record-for-alpha-decay/ https://physicsworld.com/a/bismuth-breaks-half-life-record-f...
[2] https://en.wikipedia.org/wiki/Isotopes_of_xenon#Xenon-124 https://en.wikipedia.org/wiki/Isotopes_of_xenon#Xenon-124
- kevinventullo 3y agoIf the half-life is 10^22 years, doesn’t that mean after one year you’d expect a proportion of (0.5)^(10^-22) of the atoms to be the same? This is very close to 1-A^-1 where A is Avogadro’s number. I think this means that with a mol of this stuff, you’d expect about one atom to decay after a year. If I have that right, it does seem mind blowing that they were able to detect it.
- xhrpost 3y agoAt 10^22 years, where do we draw the line between what we consider stable and what is "radioactive" or "decays"? If the heat death theory of the universe is true, then isn't everything above iron eventually going to "decay"?
- segfaultbuserr 3y agoIf proton decay is real, all atoms will eventually cease to exist, but it is still an open question. More than one experiments are still waiting for an event.
- deleted 3y ago[deleted]
- NeoTar 3y agoHalf-lives that long really begs the question to me - does every heavy nucleus (i.e. heavier than Iron-56) have a half-life? Does Gold-197 which is 'stable' actually just have a half-life of 10^50, or 10^100 years?
- fsh 3y agoThere are nuclides heavier than 56Fe, for which no decay mode is energetically allowed. 197Au is not one of them, because it could in principle do alpha decay. Wikipedia has a long list of theoretically stable nuclides (no decay mode possible), and observationally stable nuclides (at least one decay mode possible, but not observed): https://en.wikipedia.org/wiki/List_of_nuclides https://en.wikipedia.org/wiki/List_of_nuclides
- jychang 3y agoAlso, proton decay is a thing. At a certain point, if the proton is unstable, the half life of the nucleus is longer than the proton itself.
- jacquesm 3y agoThat's super impressive. How many discrete events did they observe? The Tungsten isotope page lists two alpha decays per year per gram, that must have been quite the mass of Tungsten if they got a usable signal out of that. Amazing result, if you think about it: your measurement is so accurate that you can measure you measuring gear falling apart.
- knodi123 3y agoDoes this suggest that over long enough timescales, everything is radioactive?