Speed of fusion reactions

[caters]

There are a lot of fusion reactions that go on in a star. First there are hydrogen burning ones.

• Deuterium burning
• The proton-proton chain
• The carbon-nitrogen-oxygen cycle

The Proton Proton Chain has 4 branches. It starts off like this.

The universe has just formed and there is mostly hydrogen. They all have gravity towards each other. They form a star. Now things really begin. First there is the proton-proton chain which starts off like this: 2 H -> He + y(gamma ray)

He -> D(hydrogen 2 or deterium) + e^+(positron) + ve(electron neutrino)

e^+ + e^- -> 2 y

D + H -> He3(helium 3) + y

Than the helium 3 that results goes to at least 1 of these branches

Now how fast does this whole preparation for producing heleium 4 the most common type go?

PP1(first branch)

3
2He +  3
2He →  4
2He +  2 1
1H

10 to 14 million kelvin is the dominant temperature for this.

How fast is this reaction? If we could figure that out we could multiply by the percent fo light helium that goes through this branch and the number of light helium atoms in the average star to get the average helium that reacts in this way to form stable helium.

PP2(second branch)

3
2He +  4
2He →  7
4Be +  γ 7
4Be +  e− →  7
3Li +  ν
e +  0.861 MeV /  0.383 MeV 7
3Li +  1
1H → 

2 4
2He

14 to 23 million kelvin is the dominant temperature for this

How fast are these 3 reactions?

PP3(third branch)

3
2He +  4
2He →  7
4Be +  γ 7
4Be +  1
1H →  8
5B +  γ 8
5B     →  8
4Be +  e+ +  ν
e   8
4Be     →  2 4
2He

This involves 4 reactions. How fast are these?

23 million kelvin is the dominant temperature for this.

PP4(4th and rarest branch of all)

3
2He +  1
1H →  4
2He +  e+ +  ν
e

What is the speed of this?

Next we have the CNO cycles of which there are 2 main types:

• Cold which occurs in stars
• Hot which occurs from x rays and supernovae

CNO 1

12
6C +  1
1H →  13
7N +  γ     +  1.95 MeV 13
7N     →  13
6C +  e+ +  ν
e +  1.20 MeV (half-life of 9.965 minutes^[7]) 13
6C +  1
1H →  14
7N +  γ     +  7.54 MeV 14
7N +  1
1H →  15
8O +  γ     +  7.35 MeV 15
8O     →  15
7N +  e+ +  ν
e +  1.73 MeV (half-life of 122.24 seconds^[7]) 15
7N +  1
1H →  12
6C +  4
2He     +  4.96 MeV

This CNO cycle is why carbon, nitrogen, and oxygen while they are formed later are important at the beggining.

CNO 2

This is not very common.

5
7N +  1
1H →  16
8O +  γ     +  12.13 MeV 16
8O +  1
1H →  17
9F +  γ     +  0.60 MeV 17
9F     →  17
8O +  e+ +  ν
e +  2.76 MeV (half-life of 64.49 seconds) 17
8O +  1
1H →  14
7N +  4
2He     +  1.19 MeV 14
7N +  1
1H →  15
8O +  γ     +  7.35 MeV 15
8O     →  15
7N +  e+ +  ν
e +  2.75 MeV (half-life of 122.24 seconds)

CNO 3

This only is significant in massive stars

17
8O +  1
1H →  18
9F +  γ     +  5.61 MeV 18
9F     →  18
8O +  e+ +  ν
e +  1.656 MeV (half-life of 109.771 minutes) 18
8O +  1
1H →  15
7N +  4
2He     +  3.98 MeV 15
7N +  1
1H →  16
8O +  γ     +  12.13 MeV 16
8O +  1
1H →  17
9F +  γ     +  0.60 MeV 17
9F     →  17
8O +  e+ +  ν
e +  2.76 MeV (half-life of 64.49 seconds)

CNO 4

19
9F +  1
1H →  16
8O +  4
2He     +  8.114 MeV 16
8O +  1
1H →  17
9F +  γ     +  0.60 MeV 17
9F     →  17
8O +  e+ +  ν
e +  2.76 MeV (half-life of 64.49 seconds) 17
8O +  1
1H →  18
9F +  γ     +  5.61 MeV 18
9F     →  18
8O +  e+ +  ν
e +  1.656 MeV (half-life of 109.771 minutes) 18
8O +  1
1H →  19
9F +  γ     +  7.994 MeV

HCNO 1

12
6C +  1
1H →  13
7N +  γ     +  1.95 MeV 13
7N +  1
1H →  14
8O +  γ     +  4.63 MeV 14
8O     →  14
7N +  e+ +  ν
e +  5.14 MeV (half-life of 70.641 seconds) 14
7N +  1
1H →  15
8O +  γ     +  7.35 MeV 15
8O     →  15
7N +  e+ +  ν
e +  2.75 MeV (half-life of 122.24 seconds) 15
7N +  1
1H →  12
6C +  4
2He     +  4.96 MeV

HCNO 2

15
7N +  1
1H →  16
8O +  γ     +  12.13 MeV 16
8O +  1
1H →  17
9F +  γ     +  0.60 MeV 17
9F +  1
1H →  18
10Ne +  γ     +  3.92 MeV 18
10Ne     →  18
9F +  e+ +  ν
e +  4.44 MeV (half-life of 1.672 seconds) 18
9F +  1
1H →  15
8O +  4
2He     +  2.88 MeV 15
8O     →  15
7N +  e+ +  ν
e +  2.75 MeV (half-life of 122.24 seconds)

HCNO 3

18
9F +  1
1H →  19
10Ne +  γ     +  6.41 MeV 19
10Ne     →  19
9F +  e+ +  ν
e +  3.32 MeV (half-life of 17.22 seconds) 19
9F +  1
1H →  16
8O +  4
2He     +  8.11 MeV 16
8O +  1
1H →  17
9F +  γ     +  0.60 MeV 17
9F +  1
1H →  18
10Ne +  γ     +  3.92 MeV 18
10Ne     →  18
9F +  e+ +  ν
e +  4.44 MeV (half-life of 1.672 seconds)

Deuterium burning is not very common but is important for there to be supernovae and really massive stars.

Deuterium is the most easily fused nucleus available to accreting protostars,^[1] and burning in the center of protostars can proceed when temperatures exceed 10⁶ K.^[2] The reaction rate is so sensitive to temperature that the temperature does not rise very much above this.^[2] Deuterium burning drives convection, which carries the heat generated to the surface.^[1]

If there were no deuterium burning, then there should be no stars with masses more than about two or three times the mass of the Sun in the pre-main-sequence phase because hydrogen burning would occur while the object was still accreting matter.^[2] Deuterium burning prevents this by acting as a thermostat that stops the central temperature rising above about one million degrees, which is not hot enough for hydrogen burning.^[3] Only after energy transport switches from convective to radiative, forming a radiative barrier around a deuterium exhausted core, does central deuterium burning stop. Then the central temperature of the protostar can increase.^[2][3]

The matter surrounding the radiative zone is still rich in deuterium and burning proceeds in a shell that gradually moves outwards as the star becomes more and more radiative. The generation of nuclear energy in these low-density outer regions causes the protostar to swell, delaying the gravitational contraction of the object and postponing its arrival onto the main sequence.^[2] The total energy available by deuterium burning is comparable to that released by gravitational contraction.^[3]

Due to the scarcity of deuterium in the universe, a protostar's supply of it is limited. After a few million years it will have effectively been completely consumed.^[4]

I will stop here at the hydrogen reactions until I get a reply and then we will continue the story with helium that results from hydrogen.

[Damo636]

Interesting post, but unfortunately by the time I'd understand any of it, a star would have been born and went supernova! It's times like these I wish I'd stayed a little (lot!) longer!

[old dave]

Caters

  Now that`s what I call a first post! You just took the words out of my mouth.

Come on let`s be having the next  instalment. Don`t let us pea brains put you off. We`re never too old to learn. Seriously though a good thing about this forum is the spread of knowledge and the variety of people you meet.

Listening and waiting.

Dave

[Laurie61]

     

[caters]

Okay. Next are helium burning reactions. These are the main reactions in a star besides the hydrogen burning reactions. There are two processes:

• Triple alpha process
• Alpha process

The triple alpha process is what produces carbon in the star.

4
2He + 4
2He → 8
4Be  (−93.7 keV) 8
4Be + 4
2He → 12
6C  (+7.367 MeV)

Now the negative energy I think is energy released and the positive is energy used.

The Alpha process is what produces other elements in the star from heavier elements and helium.

, Q = 7.16 МeV , Q = 4.73 МeV , Q = 9.31 МeV , Q = 9.98 МeV , Q = 6.95 МeV

Don't know if you can see it clearly but here is how it goes:

C + He -> O

O + He -> Ne

Ne + He -> Mg

Mg + He -> Si

Si + He -> S

S + He -> Ar

Ar + He -> Ca

Ca + He -> Ti

Ti + He -> Cr

Cr + He -> Fe

Fe + He -> Ni(now we are often taught that this is when the type 2 supernova starts but it really isn't)

All of these reactions up there release energy in the form of gamma rays.

Ni + He + y -> Zn(now this formation of zink uses energy and the star goes into supernova causing it to collapse)

[caters]

Now don't confuse the 2He with the 4 in the next line above it with 2 helium atoms.

[ScottS]

Ahhhhhhh I see, it's in ancient Aramaic.

[Zakalwe]

Deuterium is the most easily fused nucleus available to accreting protostars,^[1] and burning in the center of protostars can proceed when temperatures exceed 10⁶ K.^[2] The reaction rate is so sensitive to temperature that the temperature does not rise very much above this.^[2] Deuterium burning drives convection, which carries the heat generated to the surface.^[1]

If there were no deuterium burning, then there should be no stars with masses more than about two or three times the mass of the Sun in the pre-main-sequence phase because hydrogen burning would occur while the object was still accreting matter.^[2] Deuterium burning prevents this by acting as a thermostat that stops the central temperature rising above about one million degrees, which is not hot enough for hydrogen burning.^[3] Only after energy transport switches from convective to radiative, forming a radiative barrier around a deuterium exhausted core, does central deuterium burning stop. Then the central temperature of the protostar can increase.^[2][3]

The matter surrounding the radiative zone is still rich in deuterium and burning proceeds in a shell that gradually moves outwards as the star becomes more and more radiative. The generation of nuclear energy in these low-density outer regions causes the protostar to swell, delaying the gravitational contraction of the object and postponing its arrival onto the main sequence.^[2] The total energy available by deuterium burning is comparable to that released by gravitational contraction.^[3]

Due to the scarcity of deuterium in the universe, a protostar's supply of it is limited. After a few million years it will have effectively been completely consumed.^[4]

I will stop here at the hydrogen reactions until I get a reply and then we will continue the story with helium that results from hydrogen.

Interesting post, though to be fair, it would have been easier just post the Wikipedia link rather than cut and pasting it....

http://en.wikipedia.org/wiki/Deuterium_burning

[HumptyMoo]

I love that science can delve that far into the processes behind a star and it's eventual death, I also love that most of us would greet it visually with "ooooo....ahhhhhh!"

[Chris Rowland]

Interesting post, though to be fair, it would have been easier just post the Wikipedia link rather than cut and pasting it....

http://en.wikipedia.org/wiki/Deuterium_burning

Especially without crediting it.

Seriously, if you are in some sort of education don't do this for assignments.

Chris

[Zakalwe]

Especially without crediting it.

Seriously, if you are in some sort of education don't do this for assignments.

Chris

Or at least take the footnote references out....

[caters]

Now along with the alpha process and CNO cycle there are fusion reactions that fuse 2 carbon atoms.

12
6C +  12
6C →  20
10Ne +  4
2He +  4.617 MeV 12
6C +  12
6C →  23
11Na +  1
1H +  2.241 MeV 12
6C +  12
6C →  23
12Mg +  n −  2.599 MeV

and

12
6C +  12
6C →  24
12Mg +  γ +  13.933 MeV 12
6C +  12
6C →  16
8O +  2 4
2He −   0.113 MeV

all of these are carbon burning reactions. From this carbon you get oxygen, magnesium, hydrogen, helium, neon, and sodium all as atomic byproducts.

The resulting carbon burning provides energy from the core to restore the star's mechanical equilibrium. However, the balance is only short-lived; in a star of 25 solar masses, the process will use up most of the carbon in the core in only 600 years. The duration of this process varies significantly depending on the mass of the star.

Stars with below 8–9 Solar masses never reach high enough core temperature to burn carbon, instead ending their lives as carbon-oxygen white dwarfs after shell helium flashes gently expel the outer envelope in a planetary nebula.

In the late stages of carbon burning, stars with masses between 8 and 11 solar masses develop a massive stellar wind, which quickly ejects the outer envelope in a planetary nebula leaving behind an O-Ne-Na-Mg white dwarf core of about 1.1 solar masses.

Stars with more than 11 solar masses proceed with the neon-burning process after contraction of the inert (O, Ne, Na, Mg) core raises the temperature sufficiently.

[Zakalwe]

all of these are carbon burning reactions. From this carbon you get oxygen, magnesium, hydrogen, helium, neon, and sodium all as atomic byproducts.

The resulting carbon burning provides energy from the core to restore the star's mechanical equilibrium. However, the balance is only short-lived; in a star of 25 solar masses, the process will use up most of the carbon in the core in only 600 years. The duration of this process varies significantly depending on the mass of the star.

Stars with below 8–9 Solar masses never reach high enough core temperature to burn carbon, instead ending their lives as carbon-oxygen white dwarfs after shell helium flashes gently expel the outer envelope in a planetary nebula.

In the late stages of carbon burning, stars with masses between 8 and 11 solar masses develop a massive stellar wind, which quickly ejects the outer envelope in a planetary nebula leaving behind an O-Ne-Na-Mg white dwarf core of about 1.1 solar masses.

Stars with more than 11 solar masses proceed with the neon-burning process after contraction of the inert (O, Ne, Na, Mg) core raises the temperature sufficiently.

Cut and Pasted from here:

http://en.wikipedia.org/wiki/Carbon-burning_process#Stellar_evolution

Should you credit the sources when you are cutting and pasting? Or are you the author of the Wikipedia articles that you copying from?

[caters]

Wikipedia is very accurate in the science and math sections and also in music. I think that maybe I should be crediting where I am copying this from.

[Ant]

If you post again without crediting where you are posting from your time on SGL will be limited.

Thanks

Ant

[cleggy1987]

If you use lithium 6, 7.6 x 10^-23 seconds - 2.7 x 10^-20 seconds witch is used in fermal nucler weapons or li7 - 8 - 9 could you increase the power opt gained  by fusion? by 10s of thousands of times? but storeing that amount of energy maybe impossible with current technology.

Plus you have the problem of getting the power out of the fusion reactor.

But could it be used to power the spaceships of tomorrow?.

By negative chargeing protons and irons and haveing it react with anti-protons and and dark energy/matter already in space around us.

Or maybe something along those lines?.