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It is mentioned everywhere that the percentage of Uranium 235 isotope found in natural uranium is 0.711%. Samples collected from ores around the earth also seem to attest to this claim.

Is U-235 0.711 % anywhere on Earth? What about the Uranium found in Seawater? And what about elsewhere in our solar system (for example, in an asteroid near Jupiter)? If yes, why? Will it be different in a distant solar system?

From what I could gather, heavier elements like Uranium were created in a cosmic event like supernova or neutron star merger, about 6.6 billion years ago. But even if we assume that our entire solar system or Earth was created out of a small fraction of that gas cloud, is it not too improbable that the proportion of U-235 remains same everywhere on Earth (which has been observed so far) or in the entire Solar System?

Johnsmith
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    There's one well-known exception: the Oklo Mine in Gabon, where the abundance of U-235 ranged from 0.44% to 0.60%. I'll let you read the article to discover why. – Michael Seifert Oct 31 '23 at 11:20
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    The factors affecting the distribution of uranium in the Earth are nicely explained here: https://physics.stackexchange.com/q/144758/123208 But those factors don't distinguish between isotopes. What mechanism do you propose which would significantly affect the isotope ratio? – PM 2Ring Oct 31 '23 at 12:46
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    On the galactic scale, we expect some local variations, but from https://astronomy.stackexchange.com/a/16313/16685 "Mixing in the interstellar medium is reasonably effective. The material spewed out from supernovae and stellar winds 5-12 billion years ago has had plenty of time to mix throughout the Galaxy before the Sun's birth" – PM 2Ring Oct 31 '23 at 12:51
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    Isotopic differences can be used to determine where minerals originated from for, e.g., archaeological purposes. Things like determining where tin was sourced for different bronze age artifacts. – Jon Custer Oct 31 '23 at 15:19
  • @Michael Seifert I understand that the proportion of U235 was higher in the past as compared to present due to the shorter half life of U235 compared to that of U238..Also agree with your reference to Oklo natural reactor having lower than the usual U235 content, however, that can be considered as an exception. Even before the Oklo reactor started operating by itself, its U235 content would have been same as everywhere else on earth (at that time, that is around 3.1%)...My question is regarding this. Why will it be the same proportion everywhere on Earth? – Johnsmith Oct 31 '23 at 19:32
  • @PM 2Ring My only guess would be that the gas cloud that led to formation of solar system, and more specifically the Earth, was sufficiently mixed up so that it ended up creating almost same isotopic proportion everywhere – Johnsmith Oct 31 '23 at 19:35
  • @Jon Custer Do you mean to say that tin (or other elements) sourced from different locations on the Earth have significantly different isotopic proportions? That is interesting. Never heard of it before...Can you please provide some more information or references to such techniques? – Johnsmith Oct 31 '23 at 19:38
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    @Johnsmith - perhaps start with https://cordis.europa.eu/project/id/323861 or https://www.sciencedirect.com/science/article/pii/S0305440320301035 – Jon Custer Oct 31 '23 at 19:43
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    @Johnsmith The isotope concentration variations are (almost always) small. From Jon's link: "It was found that the isotope ratios of tin exhibit small but measurable variations in nature making different tin deposits identifiable". In high precision work, even the isotopic variation of water needs to be accounted for, see https://en.wikipedia.org/wiki/Vienna_Standard_Mean_Ocean_Water – PM 2Ring Oct 31 '23 at 20:02

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