metalresearcher
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Isotope distribution in the universe ?
Recently I read that the Argon distribution on Earth is mostly Ar-40 due to the decay of K-40, while on the Sun it is mostly Ar-36.
And here natural potassium contains 1 atom K-40 in each 8600 K atoms. Due to its half life, at the beginning of Earth (4.5 billion years ago) it was
2^(4.5e9/1.25e9)before now it was only 1 : 700.
Might be in (planets of) young stars like Vega, Fomalhaut there should be much more K-40, U-235 and even Pu.
Any ideas on this ?
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Endimion17
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<sup>235</sup>U is created in supernovas and it's decay constant is - a constant. It doesn't matter where are those nuclei present, it
doesn't affect them.
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blogfast25
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The isotope distribution throughout the universe does vary considerably from spot to spot although on much larger scales the universe is remarkably
homogeneous.
You should read up on 'nucleosynthesis'. Heavier elements cannot be synthesised in stars, only in the intense pressure that results from the
implosion/explosion of a giant dying star, what Endi calls correctly a 'supernova', can the intense repulsion between heavier nuclei be overcome and
result in the fusion into an even heavier element like U.
We're all star dust and the Universe is the ultimate recycling machine. It's believed our own star is second, possibly third generation...
[Edited on 15-10-2011 by blogfast25]
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Mr. Wizard
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Quote: Originally posted by blogfast25  | The isotope distribution throughout the universe does vary considerably from spot to spot although on much larger scales the universe is remarkably
homogeneous.
You should read up on 'nucleosynthesis'. Heavier elements cannot be synthesised in stars, only in the intense pressure that results from the
implosion/explosion of a giant dying star, what Endi calls correctly a 'supernova', can the intense repulsion between heavier nuclei be overcome and
result in the fusion into an even heavier element like U.
We're all star dust and the Universe is the ultimate recycling machine. It's believed our own star is second, possibly third generation...
[Edited on 15-10-2011 by blogfast25] |
I agree with your points, with a small addition. Astronomers usually consider anything above Helium and Lithium as 'heavier elements', as they were
not well represented in the aftermath of the Big Bang theory. Almost everything heavier than Hydrogen came from fusion in stars, and everything
heavier than Iron came from supernovas in stars that had burned all the fuel in their cores. The whole point, once again, is that what a chemist calls
a heavy element is different from what an astronomer or astrophysicist would call it. Sometimes they even refer to anything at or above Lithium on the
periodic table as a 'metal', which might add to confusion for the chemists here.
[Edited on 15-10-2011 by Mr. Wizard]
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blogfast25
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Seconded Mr Wizzard. There would be some logic, acc. nucleosynthesis, to call anything above Fe 'heavy', as supernovae provide a natural borderline.
But no, they prefer to try and confuse us and G-d knows we're already easily confused as it is! 
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metalresearcher
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| Quote: Originally posted by Endimion17 | | <sup>235</sup>U is created in supernovas and it's decay constant is - a constant. It doesn't matter where are those nuclei present, it
doesn't affect them. |
But the U-235 / U-238 ratio is decreasing because of the half life of U-235 is 710e6 years and U-238 4.47e9 years which is six times as long. Which
means that in young supernova remainders like the Crab Nebula (only 1000 years old) contains MUCH MORE U-235 and also a lot of short living isotopes
and will even contain Tc and Pm, but also Pu and even elements beyond it (number 95 and higher).
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Endimion17
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| Quote: Originally posted by metalresearcher | | Quote: Originally posted by Endimion17 | | <sup>235</sup>U is created in supernovas and it's decay constant is - a constant. It doesn't matter where are those nuclei present, it
doesn't affect them. |
But the U-235 / U-238 ratio is decreasing because of the half life of U-235 is 710e6 years and U-238 4.47e9 years which is six times as long. Which
means that in young supernova remainders like the Crab Nebula (only 1000 years old) contains MUCH MORE U-235 and also a lot of short living isotopes
and will even contain Tc and Pm, but also Pu and even elements beyond it (number 95 and higher).
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Exactly, but supernovas, compared to everything else in the universe, are scarce.
You mentioned Vega and Fomalhaut. Those are regular stars, and you might want to search for data on their metallicity.
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annaandherdad
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Isotope distribution: deuterium
I'll just mention that the deuterium/hydrogen ratio on earth is higher than the "primordial" ratio, the one that obtained right after the big bang.
Jupiter and the sun have roughly the primordial ratio. Astrophysicists are currently trying to figure out why earth has a higher ratio, that is, what
led to the concentration...seems that comets also have a higher ratio, and earth's water may have come from comets, where the concentration may have
taken place.
Any other SF Bay chemists?
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