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Clarify production of Ar-37

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Article says "Radioactive 37Ar is a synthetic radionuclide that is created from the neutron capture by 40Ca followed by an alpha particle emission as a result of subsurface nuclear explosions." but Isotopes of calcium says 41-Ca decays by electron capture to 41-K (not alpha emission to 37-Ar) so what is the precise sequence ? - Rod57 (talk) 14:24, 16 June 2017 (UTC)[reply]

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Updated Measurements of Ar39

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Hello folks,

There are two recent measurements of Ar39 that are relevant for this page.

The high precision measurement of Ar39 specific activity in atmospheric argon (https://link.springer.com/article/10.1140/epjc/s10052-023-11678-6) which has a value of 0.964 (± 0.001 (stat.) ± 0.024 (sys.) Bq/kg of atmospheric argon (8.6 ± 0.4 x10-16 g/g, using update half-life value from below).

New direct measurement of Ar39 using 3.4 years of atmospheric liquid argon data (https://link.springer.com/article/10.1140/epjc/s10052-025-14289-5), of 302 ± 8 (stat.) ± 6 (sys.). This value is in tension with the previous value of 269 yrs, but is a direct rather than an indirect measurement.

Comparison with earlier measurements: https://link.springer.com/article/10.1140/epjc/s10052-025-14289-5/tables/1

I've made some edits to the page to reflect this, but may not have done the references properly. For the table of isotopes, I added the systematic and statistical uncertainties of the Ar39 half-life measurement in quadrature for reporting a single uncertainty on the half-life (10 yrs).

Cheers,

ArgonMan ArgonMan (talk) 16:39, 13 July 2025 (UTC)[reply]

It appears you are part of this experiment, but I'll give you a pass for that. This measurement is problematic, though I do not believe any mathematical error was made, as it is in disagreement with the earlier measurement and does not appear to be so convincing as to disprove the old half-life. And I assume the duration of 3.4 years can't be extended, or you would have done so already - that is only 1/90 of the proposed half-life, which is a remarkably low ratio. A discrepancy like this would normally call for verification but doing so to the required accuracy would probably require 5-10 years after producing a sufficiently radio-pure sample, and I don't know if there are any plans to do so. I am not going to revert you immediately, but I'm not sure whether it should be made official here, replacing earlier data; as the stated error is worse than the current, statistics would seem to dictate at best making an average. Your paper did not, unfortunately, explore how previous estimates could have been wrong by such a surprising amount. 73.228.195.198 (talk) 00:22, 15 July 2025 (UTC)[reply]
Thanks for the follow-up. It's true that I've been involved with the group, but not with this work, and we have been separated for several years now.
None of the previous measurements are direct observations of the decays of Ar39 over extended periods. The techniques used to measure half-lives for long-lived isotopes differ from those with shorter half-lives. Ar39 is incredibly trace in atmospheric argon (x10^-16 g/g, itself only ~1% of atmosphere), and the DEAP experiment had the highest sensitivity and largest abundance of Ar39 in the world for this measurement. Large scale LAr experiments used in neutrino physics have detector energy thresholds that are too high to measure this beta decay, and next generation large LAr experiments in dark matter will remove Ar39 through enrichment (https://cds.cern.ch/record/2751036/files/scoap3-fulltext.pdf).
It's possible that the removed Ar39 could be recaptured for a dedicated measurement, as you suggest, but this would require a substantial effort and funding. Unfortunately, this is not really of interest for particle physicists, as this half-life measurement is mostly relevant for Ar-Ar geochronology.
As shown here:
https://link.springer.com/article/10.1140/epjc/s10052-025-14289-5/tables/1
The uncertainties of the individual measurements are similar, however the quoted measurement of 269 +/- 3 yrs is from 1965, and is systematically limited to the same degree, but with much less sensitive equipment.
Considerable care should be taken when averaging results from vastly different measurement techniques, and comparing the statistical uncertainties is not a sufficient gauge of a measurements' precision. Your point is valid though, but as the paper was only recently published it will take some time for people in the radiochemistry and geochronology fields to flag it for interest. I hope that researchers in those fields will take notice and consider follow-up studies. This was my motivation for posting here on the talk page and suggesting the edits, since all scientists use Wikipedia to some degree, it's a good place to share information from modern measurements of relevant physical parameters, especially across domains. ArgonMan (talk) 14:38, 15 July 2025 (UTC)[reply]
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