Talk:Proton-proton chain reaction

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It appears to me the the prep-reaction at the end of the artical is redunent. The infomation is already mentioned in the first part of the artical. But I'm not that confident with my quantum mechanics to just remove it. Lotu 04:23, 6 April 2006 (UTC)

I'm trying to understand the first step in the proton-proton chain reaction a little better. I have a question, perhaps one of you knows the answer. Where do the positron and the neutrino come from? The two protons are made up of quarks, held together by gluons. One of the protons becomes a neutron ... end result is an up quark has become a down quark. The article says that the conversion of the proton to a neutron results from the weak interaction, and the weak interaction article says something about weak interactions allowing quarks and leptons (and their antiparticles) "effectively to change into each other." This is kind of vague. Can anyone out there explain this in a little more detail. The only thing that I can think of is that some of the excess energy has been converted into matter (the positron and the neutrino) because before the reaction we have 6 quarks (two protons) and after the reaction we have 6 quarks (a proton and a neutron) PLUS a positron and a neutrino. Thanks in advance to anyone able to answer my question or confirm my guess that the positron and the neutrino effectively come from some of the excess energy being converted into matter. Sincerely, Dino.

I haven't taken a class in quantum mechanics, so you might want to take my answer with a grain of salt. I think the exces of energy comes from the fact that two protons repel each other, while a proton and a neutron in the deuterium don't. --R.Koot 04:53, 11 August 2005 (UTC)
Yes, the positron and neutrino come from the excess binding energy in 2 protons vs. a deuteron. I suspect R.Koot is right about this coming from the lack of electrostatic repulsion between the proton and neutron (not neutrino) in the deuteron, but I'm not sure. The excess energy must take the form of a positron and a neutrino, not something else, in order to satisfy conservation laws. Specifically, the 2 protons have a charge of +2, but the deuteron has a charge of +1, so a particle with positive charge (the positron) must be emitted. But the positron has a lepton number of -1, so an electron-neutrino (with a lepton number of +1 and charge of 0) must be created to balance that out. ~~ N (t/c) 05:04, 11 August 2005 (UTC)
Fusion is when an unbound state of two particles decays into a bound state by releasing energy, usually as photons. Two protons cannot fuse into helium 2 as there is no such nucleus - because of the repulsion between the protons it would have negative binding energy (i.e. more energy overall than the free particles). However the unbound state of two protons can decay into a deuterium nucleus by emitting a W+ boson, which then decays into a positron and a neutrino. This is like beta+ decay - in terms of quarks, an up-quark turns into a down-quark and a W+. This is a weak interaction, hence the low probability

Another question: "To overcome the electromagnetic repulsion between two hydrogen nuclei requires a large amount of energy, and this reaction takes an average of 10^9 years to complete. " Read as is, it suggests that two protons have to remain in each other's (weak force?) viscinity for 10^9 years before they react. This seems a bit far fetched. What was really meant? Brendan 25 April 2006

I'm also confused by this. Perhaps what is meant is that the reaction takes 10^9 years to exhaust our sun's hydrogen?
In answer to the two above posts, one way to measure reaction rates is the number of reactions per unit volume, per unit time. For example, suppose you look at one cubic metre inside the sun, for one second, and count all the p-p reactions that happen. Chances are, you won't see any because they are very rare. An alternative way to think about the same rate is to assume that you have counted one reaction in your cubic metre, and then ask the question, "How long, on average, did I have to wait to see that reaction?" The answer, in the case of the p-p reaction in the sun's core is about a billion (10^9) years. The actual collision of the protons happens very quickly.
Apetre 21:17, 5 November 2006 (UTC)

Contents

[edit] Alternate Pathway

Is there a reason why two deuterium particles cannot merge into one helium particle? Minervamoon 23:56, 9 May 2006 (UTC)

[edit] Negative Mass

The proton-proton chain reaction needs to obey the law of conservation of mass. Does it?--67.10.200.101 00:51, 1 July 2007 (UTC)

[edit] The triple-alpha process

The first sentence read as follows:

The proton-proton chain reaction is one of several fusion reactions by which stars convert hydrogen to helium, the others being the CNO cycle, and the triple-alpha process.

The triple-alpha process is not a reaction for converting H to He; it's a reaction for converting He to C. I changed this to say:

The proton-proton chain reaction is one of several fusion reactions by which stars convert hydrogen to helium, the primary alternative being the CNO cycle.

However, I think something like this would be more accurate:

The proton-proton chain reaction is one of two primary fusion reactions by which stars convert hydrogen to helium, the other being the CNO cycle.

I don't think there are "several"--other than PP, PEP, and CNO, there are no other significant reactions. But I'm not a physicist; I could be wrong, so I only went as far as my knowledge. --69.107.75.113 07:49, 16 March 2007 (UTC)

If a fraction of the proton's mass is converted to energy, will the positive charge of that partial mass go with it as well? For example , if 0.7% of the mass gets converted ,would the charge decrease by 0.7%? I am asking because when matter becomes excited (in the case of quarks) the charges all remain constant but the masses do not.

[edit] Energy/ charge release

If a fraction of the proton's mass is converted to energy, will the positive charge of that partial mass go with it as well? For example , if 0.7% of the mass gets converted ,would the charge decrease by 0.7%? I am asking because when matter becomes excited (in the case of quarks) the charges all remain constant but the masses do not.

[edit] P-P balancing CNO

I read in Kaler's text that the solar fusion is 93% P-P and 7% CNO. Extrapolating, I figure an F0V star would be half and half. Interesting! But am I correct? (I suppose I'm correct in that there's SOME point where the two reactions are equally present.) 68Kustom (talk) 10:32, 10 February 2008 (UTC)

[edit] References?

There are no external links on the page. If I add one, will it be taken off if it wasn't a source for the information? ZtObOr 00:37, 27 May 2008 (UTC)

[edit] fixed mistake in "The pp chain reaction"

I fixed a mistake in the section titled "The pp chain reaction." The text read like this:

This first step is extremely slow, because it depends on an endoergic beta positive decay, which requires energy to be absorbed, to convert one proton into a neutron. In fact this is the limiting step, with a proton waiting an average of 109 years before fusing into deuterium

This is incorrect. As shown by the equation, the reaction gives a net release of energy. I've put in the following corrected explanation:

This first step is extremely slow, both because the protons have to tunnel through the Coulomb barrier and because it depends on weak interactions. —Preceding unsigned comment added by 76.93.42.50 (talk) 17:15, 30 May 2008 (UTC)