I Chemical Elements produced inside the Sun

[DaTario]

Hi All,

I would like to know if the following statement is true or false:

The nuclear processes that happen inside the Sun can produce at least one unity of each of the known chemical elements.

Best Regards,

DaTario

 

[ChemAir]

Stellar Nucleosynthesis.

Nucleosynthesis

Some background.

 

[phyzguy]

Hi All,

I would like to know if the following statement is true or false:

The nuclear processes that happen inside the Sun can produce at least one unity of each of the known chemical elements.

What do you mean by "one unity"? One atom?

 

[stefan r]

Hi All,

I would like to know if the following statement is true or false:

The nuclear processes that happen inside the Sun can produce at least one unity of each of the known chemical elements.

Best Regards,

DaTario

False.

Lithium and plutonium come to mind.

What do you mean by "one unity"? One atom?

Assume he means one quanta. An atom. What are the odds of a ¹⁹⁷Au atom appearing?

 

[DaTario]

What do you mean by "one unity"? One atom?

Yes, at least one atom of each of the existing elements, without any external interference. Just the Sun with its initial condition and its natural burning process.

 

[DaTario]

False.

Lithium and plutonium come to mind.
Assume he means one quanta. An atom. What are the odds of a ¹⁹⁷Au atom appearing?

Hi stefan r, thank you for the response, but why are the synthesis of Lithium and Plutonium impossible in the Sun? Please note that my question does not address the discussion about abundancies. It has to do only with the possibility of the corresponding nucleosynthesis to occur in the Sun, due to internal natural processes.

 

[DaTario]

Stellar Nucleosynthesis.

Nucleosynthesis

Some background.

Thank you, Chem Air, but it seems that these pages do not contain explicitly the answer, although they contain a lot of usefull information on this subject.

 

[rootone]

A star the size of the Sun can produce Carbon,
Oxygen and Nitrogen are interesting by products of that.

 

[DaTario]

A star the size of the Sun can produce Carbon,
Oxygen and Nitrogen are interesting by products of that.

Nothing beyond these elements? Is it impossible for an atom of iron (and others havier than iron) to appear in the Sun?

 

[davenn]

Nothing beyond these elements? Is it impossible for an atom of iron (and others heavier than iron) to appear in the Sun?

no, nothing.

http://www.astronomynotes.com/evolutn/s7.htm

Created in and appearing in have 2 very different meanings.
you need to be very careful with your use of terms/definitions

That doesn't mean to say other elements are not present in stars the mass of our sun, but they were not created in the sun

 

[DaTario]

no, nothing.

http://www.astronomynotes.com/evolutn/s7.htm

Created in and appearing in have 2 very different meanings.
you need to be very careful with your use of terms/definitions

That doesn't mean to say other elements are not present in stars the mass of our sun, but they were not created in the sun

I guess I understand the difference now. Appearing suggests that the element was already present in the beginning of the star. Is it correct?
My question has to do with the creating part. By starting from hydrogen going step by step until the formation of , say, Uranium.

 

[DaTario]

http://www.astronomynotes.com/evolutn/s7.htm

From this reference, I took the following:
"The atoms heavier than helium up to the iron and nickel atoms were made in the cores of stars (the process that creates iron also creates a smaller amount of nickel too). The lowest mass stars can only synthesize helium. Stars around the mass of our Sun can synthesize helium, carbon, and oxygen. Massive stars (M* > 8 solar masses) can synthesize helium, carbon, oxygen, neon, magnesium, silicon, sulfur, argon, calcium, titanium, chromium, and iron (and nickel). Elements heavier than iron are made in supernova explosions from the rapid combination of the abundant neutrons with heavy nuclei. Massive red giants are also able to make small amounts of elements heavier than iron (up to mercury and lead) through a slower combination of neutrons with heavy nuclei, but supernova probably generate the majority of elements heavier than iron and nickel (and certainly those heavier than lead up to uranium). The synthesized elements are dispersed into the interstellar medium during the planetary nebula or supernova stage (with supernova being the best way to distribute the heavy elements far and wide). These elements will be later incorporated into giant molecular clouds and eventually become part of future stars and planets (and life forms?)"

A small part of my question is still standing on its foot. When this author, Nick Strobel, says that Stars around the mass of our Sun can synthesize helium, carbon, and oxygen. is he meaning that we are not to expect relevant amount of other heavier atoms to be produced (by nuclear processes) in the Sun or that we must accept that the Sun has not sufficient energy to produce even one atom of those heavier elements, like iron or uranium, for instance?

 

[davenn]

Appearing suggests that the element was already present in the beginning of the star. Is it correct?

Yes, they have come from other massive star supernovas and were present in the dust/gas clouds that coalesced into the sun and the planets

is he meaning that we are not to expect relevant amount of other heavier atoms to be produced (by nuclear processes) in the Sun or that we must accept that the Sun has not sufficient energy to produce even one atom of those heavier elements, like iron or uranium, for instance?

Yes, there isn't enough energy for reactions to produce those heavier elements. It takes more massive stars than our sun

Even one atom of ??
I doubt anyone could prove or disprove that and the big scheme of things, it's hardly relevant
I would rather say … detectable amounts that were guaranteed to have been CREATED in the Sun

 

[DaTario]

Thank you, davenn. Let me just present a last idea on this discussion, which is to me a bit confusing. When we study the thermal state, we learn that, at a given temperature, the probability of existence of particle with a very very high velocity is not zero, although it is very small. With this in view, must we say that the nuclear process that produces a heavier element (just one atom of it) in the Sun is, in fact, impossible?

(This ideia of thermodynamics leads me to think that it is only very unlikely to occur, but once in a while it happens, yielding a negligible population of these species.)

 

[davenn]

When we study the thermal state, we learn that, at a given temperature, the probability of existence of particle with a very very high velocity is not zero,

That's OK for things outside the core of a star.
You do know that it takes 1000's of years for photons produced in the core to get to the surface of the sun ?
there's no room for very high velocities in the core of a star... the densities are too high

 

[Bandersnatch]

I think there is always a non-zero cross section for any fusion reaction to occur, at any temperature above zero. That is to say, there is no hard cut-off absolutely preventing further steps from happening (unless there is? Let's ask @mfb ).
So the probability of there occurring the entire chain of reactions even up to uranium fusion should also have a non-zero probability.

The question would then become 'how probable is it that a star like the Sun can produce at least one of all elements, up to uranium (or even heavier), over its life time?'.
The answer would require running some actual numbers, which I don't have. My gut feeling, though, is that it'd be as probable as for a bowl of petunias to suddenly appear in Earth's orbit.

 

[mfb]

Lithium and plutonium come to mind.

Lithium is created routinely and in huge amounts in one of the proton-proton fusion chains (P-P II).
A couple of uranium atoms will capture neutrons and become plutonium. That is not a common process, but the Sun consists of 10⁵⁷ nuclei.

That's OK for things outside the core of a star.
You do know that it takes 1000's of years for photons produced in the core to get to the surface of the sun ?
there's no room for very high velocities in the core of a star... the densities are too high

The density doesn't matter as long as the system is not degenerate (it is not).

You can multiply the Gamow factor with the Maxwell-Boltzmann distribution to get a rough estimate of the probability that particles have enough energy and fuse. For two protons this chance is very small, but with the huge number of collisions it still happens once in a while. Try the same for two helium nuclei, or even heavier nuclei.

Who said it has to be fusion? Our Sun contains uranium, uranium can fission spontaneously; it releases a few neutrons in the process. The neutrons can be captured by all other elements in the Sun, often allowing them to beta decay to a different element. This is not a common process, but we have 10⁵⁷ nuclei to work with - it does happen.
In addition, cosmic rays strike the surface, leading to various reactions.

Superheavy elements would need some really weird production mechanism, however - a heavy ion coming from space hitting a heavy ion in the outer regions of the Sun or something like that. I'm not sure how often that happens. Probably more than once per 5 billion years.

 

[stefan r]

... My gut feeling, though, is that it'd be as probable as for a bowl of petunias to suddenly appear in Earth's orbit.

There is a chance that a bowl of petunias will appear in Earth's orbit. The probability of a quantum tunneling event is strongly effected by the number of particles involved and the distance that each particle moves. The atoms in your foot rearranging into a bowl of petunias at the end of your leg is much more probable than a bowl of petunias appearing in orbit unless it happens in a satellite because the particles need to move a shorter distance. The core of the sun has high density so the petunia probability should be higher. It is safe to say that a spontaneous quantum bowl of petunias is so unlikely that it has never occurred anywhere in the visible universe since the big bang.

I saw the calculations for one mole of water tunneling in a textbook. The author gave estimates for tunneling from one shot glass to an adjacent shot glass as water. That is less likely than tunneling out of the shot glass. That was much less likely than tunneling event inside the shot glass where the atoms in the water molecules move a few angstroms and become iron and release enough energy to destroy the neighborhood. Even though a spontaneous nuclear explosion in your toe is much much more likely it is still highly unlikely that is has happened anywhere in the visible universe within 4 x 10¹⁷ seconds.

If the same mechanism can happen on Earth or Ceres then I think it is reasonable to say it is not part of "the nuclear processes in the Sun".

Hi stefan r, thank you for the response, but why are the synthesis of Lithium and Plutonium impossible in the Sun? Please note that my question does not address the discussion about abundancies. It has to do only with the possibility of the corresponding nucleosynthesis to occur in the Sun, due to internal natural processes.

The core of the sun burns lithium faster than it produces lithium.

Lithium is created routinely and in huge amounts in one of the proton-proton fusion chains (P-P II).
A couple of uranium atoms will capture neutrons and become plutonium. That is not a common process, but the Sun consists of 10⁵⁷ nuclei.The density doesn't matter as long as the system is not degenerate (it is not)...

Who said it has to be fusion? Our Sun contains uranium, uranium can fission spontaneously; it releases a few neutrons in the process. The neutrons can be captured by all other elements in the Sun, often allowing them to beta decay to a different element. This is not a common process, but we have 10⁵⁷ nuclei to work with - it does happen.
In addition, cosmic rays strike the surface, leading to various reactions.

Superheavy elements would need some really weird production mechanism, however - a heavy ion coming from space hitting a heavy ion in the outer regions of the Sun or something like that. I'm not sure how often that happens. Probably more than once per 5 billion years.

I would not include cosmic ray spallation or spontaneous fission. Both can occur on Earth.

⁷Li is in the p-p chain. ⁶Li can be formed by ³H and ³He. ³H should be extremely rare. Is there an easier route to ⁶Li?

 

[mfb]

OP was talking about a single atom and the Sun. One isotope of lithium is enough and what happens on Earth is not relevant.

D + He-4 doesn’t have enough energy I guess (and photon emission - rare process if possible at all)? Can’t check right now.

 

[Bystander]

Is there an easier route to 6Li?

Along that same/similar line of inquiry, thirty to forty years ago, ⁸Be was "forbidden"/had an infinitessimal lifetime; any more recent measurements/results?

 

[mfb]

Its lifetime is still very short, $(6.7\pm1.7)\cdot 10^{-17} s$.

Edit: Minus sign

 

[Bystander]

1017s(6.7±1.7)⋅1017s(6.7\pm1.7)\cdot 10^{17} s.

Minus? Thanks.

 

[alantheastronomer]

The nuclear burning cores of sun-like stars are convective, which means they have a uniform temperature. While it's true that energies of an isotropic medium lie along a gaussian curve, with few atoms along the high end of the curve, their energies are insufficient to produce the high atomic mass elements to which you are referring.

 

[DaTario]

The core of the sun burns lithium faster than it produces lithium.

But the question posed in the OP is relative to the possibility of creation of these elements by any natural process inside the Sun; it is not related to the corresponding lifetime.

The nuclear burning cores of sun-like stars are convective, which means they have a uniform temperature. While it's true that energies of an isotropic medium lie along a gaussian curve, with few atoms along the high end of the curve, their energies are insufficient to produce the high atomic mass elements to which you are referring.

I would like to ask if you (alantheastronomer) agree with the following sentence, which is your sentence, quoted above, with a small change (bold):

The nuclear burning cores of sun-like stars are convective, which means they have a uniform temperature. While it's true that energies of an isotropic medium lie along a gaussian curve, with few atoms along the high end of the curve, their energies are insufficient to produce even just one of the high atomic mass elements to which you are referring.

 

[stefan r]

The nuclear burning cores of sun-like stars are convective, which means they have a uniform temperature. While it's true that energies of an isotropic medium lie along a gaussian curve, with few atoms along the high end of the curve, their energies are insufficient to produce the high atomic mass elements to which you are referring.

I think G and F stars do not have convective cores. convection is outside of the tachocline. Many K dwarfs are convective to the core. Types A,B,O have core convection.

 

[phyzguy]

The nuclear burning cores of sun-like stars are convective, which means they have a uniform temperature. While it's true that energies of an isotropic medium lie along a gaussian curve, with few atoms along the high end of the curve, their energies are insufficient to produce the high atomic mass elements to which you are referring.

I don't think this is true if we are talking about small quantities (like single atoms). The nuclear reactions in the sun produce free neutrons. Once free neutrons are present, you can build up heavier elements through neutron capture, which does not have a Coulomb barrier. So I think tiny quantities of all elements are built up in the sun.

 

[stefan r]

The nuclear reactions in the sun produce free neutrons.

Which fusion reaction makes free neutrons in the sun? Tritium and lithium can do it but where did they come from? Primordial T and Li should have burned before the sun reached the main sequence.

Carbon 13 + alpha could produce neutrons and will in the sun's ABG phase. The temperature dependence of triple alpha is proportional to T¹⁰ at 100 million K. The Sun has temperatures around 15.7 million degrees K and much lower density. (I did not find a link for reaction rate of ¹³C and ⁴He)

...the reaction rate should be less than ~ 10^-29 cm⁶ s^-1 mole^-2 at ~ 10^7.8 K...

So triple alpha reactions should happen somewhere in the sun within a few orders of magnitude of 1 time per year. I am going to guess that the 13C + alpha neutron source is still less than one neutron per year. In order to create lead from an iron ion the nucleus has to catch over a hundred of them before the hydrogen or ³He gets the neutron.

Once free neutrons are present, you can build up heavier elements through neutron capture, which does not have a Coulomb barrier. So I think tiny quantities of all elements are built up in the sun.

That is true for the s-process elements. Does not cover Radium, or Uranium. There are also stable isotopes that cannot be explained by the s-process.

I do not know if the neutron temperature effects the s-process. Hydrogen moderating the neutron temperature might effect the odds of creating a lead ion.

 

[alantheastronomer]

I think G and F stars do not have convective cores. convection is outside of the tachocline. Many K dwarfs are convective to the core. Types A,B,O have core convection.

The convective zone you are referring to is part of the outer layer of the sun, but the cores of sun-like stars are also convective.

 

[alantheastronomer]

But the question posed in the OP is relative to the possibility of creation of these elements by any natural process inside the Sun; it is not related to the corresponding lifetime.
I would like to ask if you (alantheastronomer) agree with the following sentence, which is your sentence, quoted above, with a small change (bold):

The nuclear burning cores of sun-like stars are convective, which means they have a uniform temperature. While it's true that energies of an isotropic medium lie along a gaussian curve, with few atoms along the high end of the curve, their energies are insufficient to produce even just one of the high atomic mass elements to which you are referring.

I stand by my statement, except for the following correction, that I meant to say "isothermal" and not "isotropic" - the energies of particles along the high end of the velocity curve are still insufficient to produce EVEN ONE of the higher mass elements.

 

[phyzguy]

Which fusion reaction makes free neutrons in the sun? Tritium and lithium can do it but where did they come from? Primordial T and Li should have burned before the sun reached the main sequence.

The proton-proton cycle fuses protons to deuterium. D + D fuses to He3 + n or T + p with equal probability, and of course D + T gives He3 + n. So, given the size of the sun, many free neutrons are produced.

That is true for the s-process elements. Does not cover Radium, or Uranium. There are also stable isotopes that cannot be explained by the s-process.

The question said one atom. There are on the order of 10^60 atoms in the sun. It didn't say anything about which isotopes, how long it takes or what the yield is. so I still think it's true that small quantities of all of the elements will be produced by neutron capture.

 

[stefan r]

The convective zone you are referring to is part of the outer layer of the sun, but the cores of sun-like stars are also convective.

This is well stated but wikipedia says the opposite. Here it says this:

In main sequence stars more than 1.3 times the mass of the Sun, the high core temperature causes nuclear fusion of hydrogen into helium to occur predominantly via the carbon-nitrogen-oxygen (CNO) cycle instead of the less temperature-sensitive proton-proton chain. The high temperature gradient in the core region forms a convection zone that slowly mixes the hydrogen fuel with the helium product.

Here it says this:

At a stellar core temperature of 18 million Kelvin, the PP process and CNO cycle are equally efficient, and each type generates half of the star's net luminosity. As this is the core temperature of a star with about 1.5 M☉, the upper main sequence consists of stars above this mass. Thus, roughly speaking, stars of spectral class F or cooler belong to the lower main sequence, while A-type stars or hotter are upper main-sequence stars.

Wikipedia also has gamma virginis as F0 V at 1.7 solar mass on this table. They have Eta Arietis as F5 V and 1.3 solar mass.

 

[jim mcnamara]

So I think tiny quantities of all elements are built up in the sun.

@phyzguy

I think we have partial verification of the claim "all elements". Could you please provide us with a citation that helps to clear this up fully? Thank you kindly...

 

[alantheastronomer]

Responding to post #31 by Stefan r - the demarcation between which stellar masses have radiative and which have convective cores is not as clear cut as Wikipedia would have you believe...However, the division between upper and lower main sequence is due to what nucleosynthetic processes govern core burning, NOT which means of energy transport occurs in the core.

 

[Vanadium 50]

The convective zone you are referring to is part of the outer layer of the sun, but the cores of sun-like stars are also convective.

I am puzzled by this as well. Figure 6-12 in Clayton suggests virtually no convection in cores of one solar mass stars.

There are on the order of 10^60 atoms in the sun. It didn't say anything about which isotopes, how long it takes or what the yield is. so I still think it's true that small quantities of all of the elements will be produced by neutron capture.

That's not as big a number as it looks. Uranium requires 237 nucleon additions. What does that mean for the probability of each nucleus to glom on another nucleon? Is it 0.1%? 1%? 10%? No - it has to be 71%, otherwise you don't get all the way to uranium.

That said, I believe every (natural) element is present in the sun, but for another reason: uranium fission. The tiny bit of primordial U-235 in the sun is exposed to neutrons and will fission.

 

[DaTario]

I believe every (natural) element is present in the sun, but for another reason: uranium fission. The tiny bit of primordial U-235 in the sun is exposed to neutrons and will fission.

So, due to the preexising Uraniun inside the Sun, which was there even before the star is born, other elements are then produced. This seems to provide a valid answer to the question in the OP, but in order to be complete, if those heavy elements were not present, would the natural ascending (starting basically from H) processes of nucleosynthesis provide all the elements?

 

[mfb]

The proton-proton cycle fuses protons to deuterium. D + D fuses to He3 + n or T + p with equal probability, and of course D + T gives He3 + n. So, given the size of the sun, many free neutrons are produced.

D+D is extremely rare. For every deuterium nucleus there are ~10¹⁷ protons around for p+D -> He-3 + photon. It does happen, so some tritium is produced. But then you have the same problem again: Deuterium is extremely rare. p+T -> He-4 + photon is much more likely than D+T -> He-4 + n. I guess a few neutrons are produced via this reaction path, but the total number must be really small.

That's not as big a number as it looks. Uranium requires 237 nucleon additions. What does that mean for the probability of each nucleus to glom on another nucleon? Is it 0.1%? 1%? 10%? No - it has to be 71%, otherwise you don't get all the way to uranium.

You don't have to start with hydrogen. The Sun contains all long-living isotopes already from its formation, for most elements you just have to add one more neutron and wait for a decay, or just wait for a decay.

That said, I believe every (natural) element is present in the sun, but for another reason: uranium fission. The tiny bit of primordial U-235 in the sun is exposed to neutrons and will fission.

The fraction of induced fission of U-235 should be tiny, but there is spontaneous fission. I said this many posts ago already.

but in order to be complete, if those heavy elements were not present, would the natural ascending (starting basically from H) processes of nucleosynthesis provide all the elements?

If the Sun would have started with hydrogen exclusively it wouldn't contain uranium by now. Probably not even iron.

 

[John Collis]

So, due to the preexising Uraniun inside the Sun, which was there even before the star is born, other elements are then produced. This seems to provide a valid answer to the question in the OP, but in order to be complete, if those heavy elements were not present, would the natural ascending (starting basically from H) processes of nucleosynthesis provide all the elements?

The short answer is no. From a fusion point of view Iron is the end of the line, to continue fusion requires energy to be input, which is why the heavier elements are formed by supernovae. Because the heavier elements are found on Earth it has been known for quite some time that the sun is at least a second generation star, but it is probably 3rd or even fourth generation.

 

[mfb]

to continue fusion requires energy to be input

There is nothing fundamentally problematic with endothermic reactions.
To study if the reaction happens you need a quantitative statement - how much energy is necessary. Too much for fusion of iron to heavier elements, but the same is true much earlier in the Sun. There is nothing special about iron in the current Sun.

 

[phyzguy]

@phyzguy

I think we have partial verification of the claim "all elements". Could you please provide us with a citation that helps to clear this up fully? Thank you kindly...

Well, I don't have a peer-reviewed document, but below is a set of lecture notes:

http://www.uio.no/studier/emner/matnat/astro/AST1100/h06/undervisningsmateriale/lecture-7.pdf

In addition to the D+D source of neutrons I mentioned earlier, this source also talks about several other sources of neutrons in the CNO cycle, which probably have higher reaction rates in the sun. From the above lecture notes:

"The r and s processes There is an exception to this temperature rule if there is a source of neutrons present as neutrons do not feel the Coulomb force. It is possible to distinguish material synthesized in a neutron rich environment from that synthesized in a neutron poor one. s-process (‘s’ for slow) elements are those formed where β-decay is expected to occur before a neutron is absorbed, while r-process 6 (‘r’ for rapid) elements are those formed where new neutrons can be absorbed readily. Sources of neutrons are various, for examples such chains as
He4 + C13 → O16 + n
O16 + 16O → S31 + n

Free neutrons produced in this manner are a way of forming elements beyond the iron peak in binding energy. In ordinary circumstances in stellar cores it is the s-processes that dominate, in extreme situations such as in supernova r-process nucleosynthesis can occur."

I'm not claiming the above reactions are common, or that the free neutrons produced are abundant, but we are talking one atom out of the ~10^59 nucleons in the solar core.

 

[Ratman]

And what are the expected lifetimes of these high-neutron isotopes? Especially compared to the time the nucleus needs to wait to capture another, and another, and another neutron? Getting from lead/bismuth to uranium is hard, and venturing into the realm of superheavies is not very probable even in environment with far higher neutron fluxes, like supernovae. Intermediates needed to clear the gaps in the nuclide chart have too short half-lives. Though it would require checking the numbers to tell how improbable it is for even one in 10⁵⁹ nucleons throughout all 10–12 billion years of Sun's existence.

 

[alantheastronomer]

I was wrong about solar mass stars having convective cores - they're radiative. But this doesn't negate the fact that temperatures in the cores of solar mass stars aren't high enough to produce elements beyond carbon, oxygen, and nitrogen, and the C-N-O cycle doesn't occur in solar mass stars. The s-process and r-process elements are produced exclusively in stars of 8 solar masses and greater.

 

[stefan r]

...The s-process and r-process elements are produced exclusively in stars of 8 solar masses and greater.

This paper says most of the s-process elements come from stars with mass 1_Θ to 3_Θ.

... But this doesn't negate the fact that temperatures in the cores of solar mass stars aren't high enough to produce elements beyond carbon, oxygen, and nitrogen, and the C-N-O cycle doesn't occur in solar mass stars. ...

They are asymptotic giant branch stars. The temperatures are far above what is needed for CNO cycle. They have helium burning in explosive flashes. The s-process elements reach the surface in a series of 3rd dredge ups.

R-coronae Borealis has a mass less than the sun. It lacks hydrogen and there is a class of objects call R-coronae borealis variables most of which also have a hydrogen shortage. The variability comes from puffs of carbon soot blowing out into a planetary nebula.

Sakurai's object is worth reading about too. It has 0.6 solar mass. It was observed coughing up s-process elements in 1996.

The Sun has some CNO cycling according to wikipedia:

pp-chain reaction starts at temperatures around 4×10⁶ K, making it the dominant energy source in smaller stars. A self-maintaining CNO chain starts at approximately 15×10⁶ K, but its energy output rises much more rapidly with increasing temperatures. At approximately 17×10⁶ K, the CNO cycle starts becoming the dominant source of energy. The Sun has a core temperature of around 15.7×10⁶ K, and only 1.7% of 4
He nuclei produced in the Sun are born in the CNO cycle.

 

[alantheastronomer]

The paper states that the s-process nuclei are produced in stars of 1.5-3 solar masses not 1-3 solar masses, but your point is well taken. Also, Ratman's comments in post #40 are entirely relevant!

 

[snorkack]

Sun is not now hot enough to produce carbon and oxygen out of helium by triple alpha process.
However, Sun is hot enough to interconvert preexisting carbon, nitrogen and oxygen by CNO cycle.
Which other preexisting elements can Sun convert?

 

[DaTario]

It seems, given what was said here so far, that, in a realistic model of the Sun, it may have (or have had at some time) the complete set of chemical elements inside, as it has come from a supernovae explosion. It seems that all these elements, specially the heavier ones, are unlikely to survive for long time.
I understand that, once all the heavier ones have been broken in small pieces, and due to the Sun's thermodynamic condition, the reposition of the complete set of chemical elements turns out to be impossible. Would this description be a reasonable synthesis of all that we had here?

 

[snorkack]

It seems, given what was said here so far, that, in a realistic model of the Sun, it may have (or have had at some time) the complete set of chemical elements inside, as it has come from a supernovae explosion. It seems that all these elements, specially the heavier ones, are unlikely to survive for long time.
I understand that, once all the heavier ones have been broken in small pieces,

How much fission does actually happen in Sun?

 

[mfb]

It seems, given what was said here so far, that, in a realistic model of the Sun, it may have (or have had at some time) the complete set of chemical elements inside, as it has come from a supernovae explosion. It seems that all these elements, specially the heavier ones, are unlikely to survive for long time.
I understand that, once all the heavier ones have been broken in small pieces, and due to the Sun's thermodynamic condition, the reposition of the complete set of chemical elements turns out to be impossible. Would this description be a reasonable synthesis of all that we had here?

The sun will keep having some uranium (and its decay products) for hundreds of billions of years, much longer than its lifetime as star.

 

[snorkack]

The sun will keep having some uranium (and its decay products) for hundreds of billions of years,

100 Gyr is 22 half-lives for U-238.

 

[DaTario]

100 Gyr is 22 half-lives for U-238.

When we speak of half-life we mean the atom left alone, don´t we?
Inside the Sun the mean durations of practically every chemical element tend to be far shorter than these estimates (half-lives), aren´t they?

 

[alantheastronomer]

When we speak of half-life we mean the atom left alone, don´t we?
Inside the Sun the mean durations of practically every chemical element tend to be far shorter than these estimates (half-lives), aren´t they?

Every RADIOACTIVE element...the abundances of these elements are far too small for chain reactions to change their half-lives appreciably!