What was the primordial composition of U isotopes in solar system?

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In summary: So, it's not clear what you're arguing. There's no mention of thorium in that article.In summary, the primordial composition of U isotopes in solar system was uranium 238, uranium 234, uranium 235, and plutonium 244. All other isotopes were products of decay of these initial elements. There was a primordial abundance of uranium 236, but excess uranium 236 has not been found in solar system since it decayed.
  • #1
snorkack
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What was the primordial composition of U isotopes in solar system?

Solar system contained isotopes less than a million year halflife, because meteors have clear traces of having crystallized with abundant aluminium 26.

So, what was the actinide composition?

We know the exact amount of uranium 238 because her longest lived mother is Pu-242, half-life 373 000 years. All uranium 238 was in Solar System primordially - she has only decayed since, at a predictable rate and known final amount.

Not so with uranium 235. For though the halflife of U-235 and remaining amount is known, U-235 unlike U-238 has a long lived mother - Cm-247 with half-life of 15,6 million years.

Since Cm-247 is now completely extinct, is it known what fraction of U-235 was primordial and what fraction is daughter of Cm-247?

Now, concerning uranium...
Uranium 236 is also an isotope of uranium. She is herself long lived - 23,5 million years half-life - and daughter of even longer lived - 80 million years - plutonium 244.
Considering uranium 236 and plutonium 244 are both long lived, did primordial solar system contain excess uranium 236 (primordial amounts) or was the solar system short of uranium 236 till she formed by decay of plutonium 244?

Finally, neptunium 237 has a half-life 2,2 million years. Her daughters include uranium 233.

Therefore, the primordial U composition would have been:
U-238 (all there, known amount)
U-234 (already in equilibrium as daughter of U-238, so known amount)
U-235 (how much had formed?)
U-236 (how much was there?)
U-233 (same question)

Can anyone provide the numbers for that isotopic composition?
 
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  • #2
These isotopes are mainly by products of U238 and thorium decay. Their natural abundance is related to their half life and abundance of progenitors. All elements heavier than iron/nickel are the result of supernovae. It is reasonable to assume they originated in relatively nearby supernovae before the solar system evolved.
 
  • #3
Chronos said:
These isotopes are mainly by products of U238 and thorium decay.
No. Only uranium 234 is. The others - uranium 235, uranium 233, uranium 236 and also traces of uranium 240 - most emphatically cannot be formed by decay of uranium 238, nor thorium.
Rather they are products of neptunium, plutonium and curium decay.
Chronos said:
Their natural abundance is related to their half life and abundance of progenitors.

Half lives of progenitors are known. I quoted all of them. But my question is, what were the primordial abundances of progenitors?
 
  • #4
Apologies for the decay chain confusion. Only two uranium isotopes are primordial [birthed by supernova] - U238 and U235. Plutonium 244 is the primordial nuclide that 'mothers' a decay chain producing U240, U236, U233, and U232. U233 is not produced by any known natural decay process. It is known from meteorite studies that no less that 10 progenitor stars contributed to primordial nuclides in the solar system. If you were to assume [erroneously] a single progenitor supernova was responsible for all the uranium in the solar system, it must have occurred about 6.5 billion years ago. See http://world-nuclear.org/info/Nuclear-Fuel-Cycle/Uranium-Resources/The-Cosmic-Origins-of-Uranium/ for discussion.
 
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  • #5
Chronos said:
Plutonium 244 is the primordial nuclide that 'mothers' a decay chain producing U240, U236, U233, and U232. U233 is not produced by any known natural decay process.

Look at the contradiction between your two consecutive sentences!
U-232 is not produced as a daughter of Pu-244, because U-236 undergoes alpha decay to Th-232, which does not undergo beta decay, but alpha decay (to Ra-228).
U-233 is, as I posted above, produced as a daughter of Np-237 so long as Np-237 (half-life 2,2 million years) remains in nature.
 
  • #6
Agreed, inclusion of U233 in the Pu244 decay chain was unintended, as evidenced by the sentence that followed. Take a look at http://periodictable.com/Isotopes/094.244/index.full.html. Given that Thorium 232 is considered primordial, it is not necessary to trace its ancestry back to Pu244 to account for natural production of U232. It is, however, necessary to account for natural production of U236 and U240 in a primordial nuclide decay chain. I may have missed something, but, it does not appear there is any primordial nuclide that naturally produces U233 in its decay chain. It should be noted that Np237 is not considered a primordial nuclide. For a listing of primordial nuclides see http://en.wikipedia.org/wiki/Primordial_nuclide.
 
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  • #7
Chronos said:
Given that Thorium 232 is considered primordial, it is not necessary to trace its ancestry back to Pu244 to account for natural production of U232.
But that´s a fine line. Very fine considering that it is double beta - in fact, there is no actual decay fraction given, so the claim that thorium 232 might undergo double beta is unproven.
Chronos said:
It is, however, necessary to account for natural production of U236 and U240 in a primordial nuclide decay chain. I may have missed something, but, it does not appear there is any primordial nuclide that naturally produces U233 in its decay chain. It should be noted that Np237 is not considered a primordial nuclide. For a listing of primordial nuclides see http://en.wikipedia.org/wiki/Primordial_nuclide.

But that list also omits Al-26, I-129 etc., which are proven to have existed in young solar system. So the omission of Np-237 merely shows that it has decayed since, not that it was not present in nature.
What then were the original ratios in young solar system of:
Pu-244/Th-232?
Cm-247/U-235?
Np-237/Bi-209?
 
  • #8
As already explained, the abundance of primordial nuclides in the solar system is not calculable. They can only be measured. This is problematic for nuclides with short half lives [i.e. less than 80 million years] which are considered non-primordial - as is the case for Al26, I129 and Np237. Any such nuclides that currently exist in the solar system are necessarily the result of the decay chain of longer lived primordial nuclides. [see http://en.wikipedia.org/wiki/List_of_nuclides] [Broken]. Pu244 is at the edge of detectability on this basis. It appears you are less interested in the original question than arguing the details.
 
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  • #9
Chronos said:
As already explained, the abundance of primordial nuclides in the solar system is not calculable.
Precisely. I explained it.
Chronos said:
They can only be measured.
Precisely.
Chronos said:
This is problematic for nuclides with short half lives [i.e. less than 80 million years] which are considered non-primordial - as is the case for Al26, I129 and Np237. Any such nuclides that currently exist in the solar system are necessarily the result of the decay chain of longer lived primordial nuclides.
Or formed recently in different manners, like radiogenic. So measuring their present abundance measures their present production mechanisms, not their primordial amounts.
Chronos said:
It appears you are less interested in the original question than arguing the details.
No. I am interested exactly in the original question. I need to argue the details because they are offered instead of the original question.
It is possible to measure primordial abundances of extinct isotopes by measuring their daughters in meteors.
What have been the measured primordial abundances of the long-lived extinct actinids - Pu-244, U-236, Cm-247 and Np-237?
 
  • #10
snorkack said:
It is possible to measure primordial abundances of extinct isotopes by measuring their daughters in meteors.
Tricky. You can measure the current abundances, but it is hard to impossible to determine which (relatively) short-living isotope started the chain.
 
  • #11
mfb said:
Tricky. You can measure the current abundances, but it is hard to impossible to determine which (relatively) short-living isotope started the chain.

But if they are different element then they should have different chemical behaviour.
Extant actinides:
Th is always 4+. Impossible to oxidize or reduce. Crystal radius 108 nm. It is a highly incompatible element - a strong field cation.
U has oxidation state options. But U3+ is a very strong reducer. UO2(2+) is common on modern Earth - with free dioxygen available. In ordinary space, U would also be U4+ - crystal radius 103 nm.

By contrast, look at the extinct actinides:
Np is on modern Earth easily oxidized to Np4+ or NpO2+, and with some difficulty to NpO2(2+). But under ordinary reducing conditions, where U is U4+ rather than UO2(2+), Np is Np3+ rather than Np4+. And the crystal radius of Np3+ is 115 nm - compare Ce3+, also 113 nm.
Pu is oxidized to Pu4+, PuO2+ or PuO2(2+), with some difficulty - and easily reduced to Pu3+, crystal radius 114 pm, compare Pr3+, 113 pm.
Cm is very hard to oxidize, and is Cm3+ under any common conditions - crystal radius 111 nm, compare Nd3+, 112 nm, and Sm3+, 110 nm.

It seems to me that there is a gross difference in chemical behaviour - long-lived U and Th (together with their extinct isotopes like U-236) should have entered minerals as strong field incompatible cations, whereas the extinct transuranium elements should have partitioned with ceria Earth's.
 
  • #12
Just to ensure we are talking about the same thing, here is the OP:
snorkack said:
What was the primordial composition of U isotopes in solar system?

Solar system contained isotopes less than a million year halflife, because meteors have clear traces of having crystallized with abundant aluminium 26.

So, what was the actinide composition?

We know the exact amount of uranium 238 because her longest lived mother is Pu-242, half-life 373 000 years. All uranium 238 was in Solar System primordially - she has only decayed since, at a predictable rate and known final amount.

Not so with uranium 235. For though the halflife of U-235 and remaining amount is known, U-235 unlike U-238 has a long lived mother - Cm-247 with half-life of 15,6 million years.

Since Cm-247 is now completely extinct, is it known what fraction of U-235 was primordial and what fraction is daughter of Cm-247?

Now, concerning uranium...
Uranium 236 is also an isotope of uranium. She is herself long lived - 23,5 million years half-life - and daughter of even longer lived - 80 million years - plutonium 244.
Considering uranium 236 and plutonium 244 are both long lived, did primordial solar system contain excess uranium 236 (primordial amounts) or was the solar system short of uranium 236 till she formed by decay of plutonium 244?

Finally, neptunium 237 has a half-life 2,2 million years. Her daughters include uranium 233.

Therefore, the primordial U composition would have been:
U-238 (all there, known amount)
U-234 (already in equilibrium as daughter of U-238, so known amount)
U-235 (how much had formed?)
U-236 (how much was there?)
U-233 (same question)

Can anyone provide the numbers for that isotopic composition?
Let's start with the initial question - "What was the primordial composition of U isotopes in solar system?" There are 288 nuclides that were produced in stars AND have half lives long enough to remain in detectable amounts [i.e., are PRIMORDIAL]. A list of these nuclides is here: http://en.wikipedia.org/wiki/List_of_nuclides. You will note that U238 and U235 are the only isotopes of uranium listed as primordial. All other uranium isotopes are either of cosmogenic or radiogenic origin, and NOT PRIMORDIAL.

Moving on to the next statement - " Solar system contained isotopes less than a million year halflife, because meteors have clear traces of having crystallized with abundant aluminium 26. So what was the actinide compositiont?" Al26 is believed to be of cosmogenic origin. This article might be of interest: http://iopscience.iop.org/0004-637X/489/1/346/fulltext/

Moving on to the next statement - "We know the exact amount of uranium 238 because her longest lived mother is Pu-242, half-life 373 000 years. All uranium 238 was in Solar System primordially - she has only decayed since, at a predictable rate and known final amount." U238 is primordial whereas none of its mother isotopes are considered primordial.

And next - "Not so with uranium 235. For though the halflife of U-235 and remaining amount is known, U-235 unlike U-238 has a long lived mother - Cm-247 with half-life of 15,6 million years.
Since Cm-247 is now completely extinct, is it known what fraction of U-235 was primordial and what fraction is daughter of Cm-247?" It is likely impossible to deduce how much U235 was a daughter of Cm247 and how much was produced directly by supernova. See http://world-nuclear.org/info/Nuclear-Fuel-Cycle/Uranium-Resources/The-Cosmic-Origins-of-Uranium/ for further discussion.

And lastly- "Now, concerning uranium...
Uranium 236 is also an isotope of uranium. She is herself long lived - 23,5 million years half-life - and daughter of even longer lived - 80 million years - plutonium 244.
Considering uranium 236 and plutonium 244 are both long lived, did primordial solar system contain excess uranium 236 (primordial amounts) or was the solar system short of uranium 236 till she formed by decay of plutonium 244? Finally, neptunium 237 has a half-life 2,2 million years. Her daughters include uranium 233. " The amount of Pu244 currently present in the solar system is at our limits of detectability. The amount of U236 and Np237 currently present is beyond detectable limits. It is thus very difficult/impossible to assess the abundance of non primordial nuclides in the pre solar nebula. Chances are their abundance was negligible in the pre solar nebula. This is true of any non primordial nuclide.
 
  • #13
Chronos said:
Just to ensure we are talking about the same thing, here is the OP:

Let's start with the initial question - "What was the primordial composition of U isotopes in solar system?" There are 288 nuclides that were produced in stars AND have half lives long enough to remain in detectable amounts [i.e., are PRIMORDIAL]. A list of these nuclides is here: http://en.wikipedia.org/wiki/List_of_nuclides. You will note that U238 and U235 are the only isotopes of uranium listed as primordial. All other uranium isotopes are either of cosmogenic or radiogenic origin, and NOT PRIMORDIAL.
Yes, but that depends on the definition of "primordial" adopted by Wikipedia. I did not ask what the "primordial" U isotopes are now, I asked what they were, then. So what term would you prefer for isotopes formed in star, neither cosmogenic nor radiogenic, that existed in young solar system but have since decayed?
Chronos said:
Moving on to the next statement - " Solar system contained isotopes less than a million year halflife, because meteors have clear traces of having crystallized with abundant aluminium 26. So what was the actinide compositiont?" Al26 is believed to be of cosmogenic origin. This article might be of interest: http://iopscience.iop.org/0004-637X/489/1/346/fulltext/
Al-26 is easily formed cosmogenically and small amounts are formed now. Yet young solar system contained much bigger amounts than was around later.
Chronos said:
And next - "Not so with uranium 235. For though the halflife of U-235 and remaining amount is known, U-235 unlike U-238 has a long lived mother - Cm-247 with half-life of 15,6 million years.
Since Cm-247 is now completely extinct, is it known what fraction of U-235 was primordial and what fraction is daughter of Cm-247?" It is likely impossible to deduce how much U235 was a daughter of Cm247 and how much was produced directly by supernova. See http://world-nuclear.org/info/Nuclear-Fuel-Cycle/Uranium-Resources/The-Cosmic-Origins-of-Uranium/ for further discussion.
Discussion that makes no mention whatever of Cm-247
Chronos said:
The amount of U236 and Np237 currently present is beyond detectable limits. It is thus very difficult/impossible to assess the abundance of non primordial nuclides in the pre solar nebula. Chances are their abundance was negligible in the pre solar nebula. This is true of any non primordial nuclide.
Manifestly untrue for Al-26, therefore why not for U-236?
 
  • #14
The definition of a primordial nuclide is "In geochemistry and geonuclear physics, primordial nuclides, also known as primordial isotopes, are nuclides found on the Earth that have existed in their current form since before Earth was formed. Primordial nuclides are residues from the Big Bang, from cosmogenic sources, and from ancient supernova explosions which occurred before the formation of the solar system. They are the stable nuclides plus the long-lived fraction of radionuclides surviving in the primordial solar nebula through planet accretion until the present. Only 288 such nuclides are known." [re: http://en.wikipedia.org/wiki/Primordial_nuclide] [Broken].

Extinct nuclides is evidently the term we are struggling with to reach consensus - "An ‘extinct radionuclide’ is understood to be one that was formed by a process of stellar nucleosynthesis prior to the coalescence of the solar-system, and which has subsequently decayed away to zero." [re: http://www.onafarawayday.com/Radiogenic/Ch15/Ch15-1.htm] [Broken] Estimated abundances of some extinct nuclides in the pre solar nebula is given by table 1 of this paper - http://arxiv.org/abs/1105.5172. Contributions to daughter nuclides by sources other than extinct nuclides, such as Al26 and I129, complicate quantification of extinct nuclide abundances. See http://arxiv.org/abs/astro-ph/9605128.

I was unable to find any information on the estimated abundance of U236 in the pre solar nebula.
 
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  • #15
Chronos said:
Estimated abundances of some extinct nuclides in the pre solar nebula is given by table 1 of this paper - http://arxiv.org/abs/1105.5172.

Thanks! Finally roughly what I wanted.
 
  • #16
I'm pleased we arrived on the same page. I accept most of the credit for obfuscating matters.
 
  • #17
So:
Cm-247 has been found - to one star confidence. The amount was small, however. By my calculations, it is making the difference between original U-235 concentration of either 24,2197 % or 24,2156 % - so just 0,018 % of U-235 originates from decay of primordial Cm-247. This comes from detected variations of U-235/U-238 ratios in meteors.
By my computations, neglecting the primordial U-236 and Np-237 (not mentioned in the article quoted), the original U composition 4566 million years ago should have been, within tenths of %:
75,6 % U-238
24,2 % U-235
0,2 % U-236
Is it correct, or do you want to see the details of my computations?
 
  • #18
The present ratio of U238 to U235 is about 99.3% vs 0.7%. Did you derive their primordial abundances by extrapolating back using standard decay rates? As far as I know this will only yield approximate abundances at any given point in history. Meteorite studies suggest variations in the abundance of pristine and 'mother' nuclides over time - probably a consequence of injection of these isotopes in variable quantities from multiple supernovae sources. I have no clue how to calculate primordial U236 abundances. I am curious about that computation.
 
  • #19
Chronos said:
The present ratio of U238 to U235 is about 99.3% vs 0.7%. Did you derive their primordial abundances by extrapolating back using standard decay rates?
Yes.
Chronos said:
I have no clue how to calculate primordial U236 abundances. I am curious about that computation.

Calculate or measure?
As I stated, I found no information about primordial U-236, and said I neglected it.
So I assumed that primordial U-236 was in equilibrium with her mother Pu-244.

Now if a daughter is longer lived than mother then she can never come into equilibrium with mother. The ratio of daughter to mother will diverge to infinity as mother decays exponentially and the daughter, not so fast.

Equilibrium is impossible no matter how slightly longer lived the daughter is. Therefore the ratio of daughter to mother will diverge to infinity even when their lifetimes are exactly equal.
My guess was that the equilibrium ratio of U-236 to Pu-244, given their half-lives 23,48 and 80 million years respectively should have been 23,48/(80-23,48). Can anyone tell if the guess is correct?
Now given that the primordial ratio of Pu-244 to U-238 was measured as 0,68%+-0,10 % (in the source), the primordial ratio of U-236 to U-238 comes out as 0,28 %. And given about 75 % total U-238 (most of the rest primordial U-235) is how I got 0,21 % U-236.
 
  • #20
Such calculations are difficult because of contributions from nearby supernovae and galactic sources, which are necessarily of different ages. The estimated abundances U235, U238 and Th232 resulting from nucleosynthesis are summarize here, http://adsabs.harvard.edu/full/1964ApJ...139..637C. The initial ratio of Pu244 to U238 is estimated to be about 7x10E-3 per http://www.uapress.arizona.edu/onlinebks/PPIV/chap35.pdf. The relative contribution by the ISM vs supernovae is, however, difficult to quantify. My best guess as to abundances in the presolar nebula, based solely on nearby supernovae contributions, would be about 61% U235, 39% U238 and .003% Pu244.
 
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  • #21
Chronos said:
My best guess as to abundances in the presolar nebula, based solely on nearby supernovae contributions, would be about 61% U235, 39% U238 and .003% Pu244.

Where do you think did U 235 go, then?
 
  • #22
By the time primordial U238 completed 1 decay cycle, primordial U235 would have completed 6.32 decay cycles. Based on an initial abundance of about 60% U235 to 40% U238, the ratio of U235 to U238 remaining would be about 0.77% to 20%. Of course, that ignores ISM contributions which would further dilute this ratio.
 
  • #23
Chronos said:
By the time primordial U238 completed 1 decay cycle, primordial U235 would have completed 6.32 decay cycles. Based on an initial abundance of about 60% U235 to 40% U238, the ratio of U235 to U238 remaining would be about 0.77% to 20%.
Or about 3,7 % to 96,3 %. Yes. But this is not what the present abundance is.
So when was there 60 % U-235?
 
  • #24
Based on stellar nucleosynthesis models, the production ratio of U235 to U238 is 1.65. If all the uranium in the presolar nebula was freshly minted by a nearby supernova, the ratio should be 62.3% U235 [1.65/2.65] and 37.7% U238. Based on present abundances of 99725 U238 atoms and 720 U235 atoms, uranium abundance in the presolar nebula one U238 decay cycle in the past should be 58666 U235 atoms and 198550 U238 atoms for every 257216 total uranium atoms, or 22.8% U235 and 77.2% U238 atoms. At 1.47 U238 decay cycles in the past, the numbers would have been would have been 265013 U238 to 464072 U235, or at nucleosynthesis abundances of 62.3% U235 and 37.7% U238. If all the uranium in the presolar nebula originated from a single supernova, it had to occur about about 6.5 billion years ago [1.47 U238 decay cycles]. Since the Earth is only about 4.5 billion years old, uranium at near nucleosynthesis abundances must have been mixed with older ISM uranium at lower concentrations to explain current measured ratios.
 

1. What is Primordial U composition?

Primordial U composition refers to the abundance and distribution of uranium (U) in the early universe, specifically during the first few hundred million years after the Big Bang. It is a key factor in understanding the formation and evolution of the universe.

2. How is Primordial U composition measured?

Primordial U composition is measured through the analysis of ancient rocks and meteorites, which contain traces of U that have remained unchanged since the early universe. Scientists also use data from cosmic microwave background radiation and nuclear reactions in stars to determine the primordial U abundance.

3. Why is Primordial U composition important?

Primordial U composition provides insights into the conditions of the early universe and helps us understand the processes that led to the formation of galaxies, stars, and planets. It also has implications for the production of heavy elements and the potential for life-supporting planets.

4. How does Primordial U composition affect our understanding of nuclear reactions?

The abundance and distribution of U in the early universe plays a crucial role in our understanding of nuclear reactions, as U is a key element in nuclear fusion and fission processes. Studying primordial U composition can help us improve our understanding of these reactions and their role in the evolution of the universe.

5. Is Primordial U composition consistent throughout the universe?

While the overall abundance of U is thought to be consistent throughout the universe, there may be variations in the distribution of U in different regions. This is due to the complex processes involved in the formation and evolution of the early universe, which could lead to differences in the primordial U composition in different areas.

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