While trying to solve the "clumping problem" in my scifi, I suddenly have an idea:

What if we try to fuse a single proton and a neutron together?
I then briefly read about the criteria for fusion in wikipedia:

The origin of the energy released in fusion of light elements is due to an interplay of two opposing forces, the nuclear force which draws together protons and neutrons, and the Coulomb force which causes protons to repel each other. Because the nuclear force is stronger than the Coulomb force for atomic nuclei smaller than iron and nickel, building up these nuclei from lighter nuclei by fusion releases the extra energy from the net attraction of these particles. For larger nuclei, however, no energy is released, since the nuclear force is short-range and cannot continue to act across still larger atomic nuclei. Thus, energy is no longer released when such nuclei are made by fusion (instead, energy is absorbed in such processes).

The situation is similar if two nuclei are brought together. As they approach each other, all the protons in one nucleus repel all the protons in the other. Not until the two nuclei actually come in contact can the strong nuclear force take over. Consequently, even when the final energy state is lower, there is a large energy barrier that must first be overcome. It is called the Coulomb barrier.
The Coulomb barrier is smallest for isotopes of hydrogen, as their nuclei contain only a single positive charge. A diproton is not stable, so neutrons must also be involved, ideally in such a way that a helium nucleus, with its extremely tight binding, is one of the products.

I then tried to google "proton neutron collision, proton neutron fusion, but found nothing, instead I stumbled upon these

http://en.allexperts.com/q/Physics-1358/neutron-neutron-fusion-easier-1.htm
The first guy said n-n fusion might be energy generating and show 4 links in the article
www.fnal.gov/pub/inquiring//virtual/aas_transcript (broken link)
adsabs.harvard.edu/abs/2005nucl.th...7048A
eprintweb.org/S/article/nucl-th/0507048
http://legacyweb.triumf.ca/publications/pub/arch05/pp-05-25.pdf (actual article itself)
Which all are the same article
http://www.sciencedirect.com/science/article/pii/S0370269305017491 (Leads to a presumably peer reviewed article which I fail to understand)

I then saw this reaction in the article

n + n → d + e¯+ ¯νe (where d=dineutron)

However another guy
http://en.allexperts.com/q/Nuclear-Power-2462/neutron-neutron-fusion-easier-1.htm
He mentioned the intensity of neutron in neutron beams are too low and the n-n interactions is too low to be viable

Also some guys in physicsforums (which also stumbled upon from google)
http://www.physicsforums.com/showthread.php?t=206382
Mentioned that dineutron is unstable thus the n-n fusion is energy absorbing instead of energy releasing (I'm not sure whether it also apply to the equation quoted from the article above)
(Note that the n-n question is asked by the same person: Green)
Now back to the main point

If we fuse n+p together then we should get deutrium nuclei which is stable
Moreover similar to the n-n fusion (which IMO is quite improbable) the columb force does not exist between the proton and the neutron as neutrons are electrically neutral, thus there is little effort to bring the nucleons together

IMO I think it will look like this:
n+p+->D (I cannot see any reason for any neutrinos to be produced in the process, as the neutron does not need to decay when in a nucleus. However it might be possible but I am not sure since I'm not familiar with quantum field theory)
Or
n+H->D




However when considering the 1st wikipedia quote, I then have the following questions
1. Will the two nucleons fuse together when they get close enough for the nuclear force to act between them, or will they just bounce away?
2. If 1 is possible, is the energy of D lower than that of n+p combined?
3. According to 1st wikipedia quote, the extra energy released from the fusion process is due to the columb force and the nuclear force. In the n+p case there is no columb force. Does that means there will be no energy released in this process?
4. In the second hypothetical case, will there be a significant probability that the neutron will absorb the electron of the hydrogen atom and then become the proton, thus preventing the two nucleons from fusing together?

Since you numbers your questions I'll just number my answers....

1. Yes, though how close depends on the nucleons. p+p \to D + \ldots is possible, it's one of the steps in building up the higher elements from just Hydrogen. If it didn't work we wouldn't exist. But that doesn't mean it's easy. The Sun is mostly free protons by mass (the free electrons which partner them as 1/2000 the mass) and despite the core being 15 million Kelvin and many times denser than Lead the average proton will bounce around for billions of years before having another collision with a proton which is close enough to precisely head on, at high enough energy, that they'll fuse into Deuterium. Fortunately there's a lot of protons in the Sun so statistically billions of tons of them manage it every second (releasing millions of tons of energy).

n-n I'd almost expect to be easier, since they don't repel one another. However, neutrons decay with a half life of 11 minutes when not bound with something else so they won't last long. Outside of very very rare instances or artificially orchestrated setups like we make in experiments I doubt this is a main channel for any processes.

p-n collisions will be many orders of magnitude more likely, since each neutron will have many protons around it and there's still no repulsion between them so if Deuterium is energetically favourable to separate p and n I imagine this will happen quite a lot in a star, which brings us to question 2.

2. I'm not familiar enough with this stuff to know the numbers off the top of my head but I would have thought so, else Deuterium would decay because it would be energetically favourable. Tritium is unstable and has a half life in the years (a decade or so?) but Deuterium is considered completely stable.

3. If there's 2 possible forces involved and one of them isn't how do you reach the conclusion no energy is involved? What about the strong force? Nucleon interactions aren't governed by gluon interactions, which is what the strong force is. They are governed by meson interactions giving rise to a Yukawa force, an effective field theory (http://en.wikipedia.org/wiki/Effective_field_theory) for QCD.

The Yukawa force is stronger than the EM force, though not as strong as the strong force. Nucleons will only see their neighbours via the Yukawa force but protons will see all the protons in the nucleus because the EM force is longer range. This is why trans-Lead elements are unstable, there's so many protons all pushing one another that the neighbour to neighbour Yukawa attraction can't hold it together forever. However, in the case of something like Tritium, where there's no real EM repulsion, the instability is Yukawa force related.

It is worth pointing out that when nucleons are really close (certainly as is the case at the LHC) then they can see one another's quarks. A neutron is overall neutral but it still have very weak EM properties because it's got 3 charges inside it, it's a tripole. As such there will be very slight EM corrections to all of this stuff but it'll be small compared to the Yukawa dynamics.

4. Although you can write such a process as p+e \to n (up to a neutrino) what really happens is generally the proton decays into a neutron and spits out a positron. Then the positron ends up hitting an electron. Electron capture can occur but it's less straight forward because you need a huge bath of electrons to drive the process. A proton with too much energy can spit out a positron (and electron neutrino) all by itself.

You should bear in mind that for these sorts of processes the specific quantitative stuff is very difficult to compute. What holds nucleons together is the residual Yukawa force of the strong force. What pushes them apart is both the Yukawa and EM force. And what causes protons and neutrons to turn into one another is the electroweak force. There's all sorts of non-perturbative effects and electroweak corrections and Yukawa limits flying around the calculations, much of which we're only just beginning to do on supercomputers you could chock an elephant with (please, no one chock an elephant with a computer). In principle any one of the possible transitions we're talking about can occur. The sticking point is how often they occur relative to one another, what conditions they prefer or create and how stable are the results.

What precisely are you needing this information for in regards to scifi?

1. Yes, though how close depends on the nucleons. p+p \to D + \ldots is possible, it's one of the steps in building up the higher elements from just Hydrogen. If it didn't work we wouldn't exist. But that doesn't mean it's easy. The Sun is mostly free protons by mass (the free electrons which partner them as 1/2000 the mass) and despite the core being 15 million Kelvin and many times denser than Lead the average proton will bounce around for billions of years before having another collision with a proton which is close enough to precisely head on, at high enough energy, that they'll fuse into Deuterium. Fortunately there's a lot of protons in the Sun so statistically billions of tons of them manage it every second (releasing millions of tons of energy).

n-n I'd almost expect to be easier, since they don't repel one another. However, neutrons decay with a half life of 11 minutes when not bound with something else so they won't last long. Outside of very very rare instances or artificially orchestrated setups like we make in experiments I doubt this is a main channel for any processes.

p-n collisions will be many orders of magnitude more likely, since each neutron will have many protons around it and there's still no repulsion between them so if Deuterium is energetically favourable to separate p and n I imagine this will happen quite a lot in a star, which brings us to question 2.

@1st block (of text) I first know of this when I was browsing that wikipedia article to set up this thread. However I didn't expect it is difficult for the protons to collide despite the sun is very dense

@2nd block
When I first saw this reactions asked by Green in the physicsfroums (via today's google search) the first hting come to mind that will limit this reaction is the short half life of neutron (still it is longer than I expected, I thought it was just in the order of seconds!). Only after reading the other google search links and marlon's reply to green I realise the dineutron is unstable. Thus after all of this I just rule this out as a viable fusion source

@3rd block
to Q 2


2. I'm not familiar enough with this stuff to know the numbers off the top of my head but I would have thought so, else Deuterium would decay because it would be energetically favourable. Tritium is unstable and has a half life in the years (a decade or so?) but Deuterium is considered completely stable.

Yup
Hmm seemed it will be quite a possibility, I'll leave that for later until I can gain access to some convenient neutron sources
Planned expt: place a neutron source in a gas of hydrogen? (This sentense is a rhetorical question, so just ignore it)
More importantly, when I finally gain access to the maths required to compute this thing (won't be far away as I'm in year 1 now)


3. If there's 2 possible forces involved and one of them isn't how do you reach the conclusion no energy is involved? What about the strong force? Nucleon interactions aren't governed by gluon interactions, which is what the strong force is. They are governed by meson interactions giving rise to a Yukawa force, an effective field theory (http://en.wikipedia.org/wiki/Effective_field_theory) for QCD.

The Yukawa force is stronger than the EM force, though not as strong as the strong force. Nucleons will only see their neighbours via the Yukawa force but protons will see all the protons in the nucleus because the EM force is longer range. This is why trans-Lead elements are unstable, there's so many protons all pushing one another that the neighbour to neighbour Yukawa attraction can't hold it together forever. However, in the case of something like Tritium, where there's no real EM repulsion, the instability is Yukawa force related.

It is worth pointing out that when nucleons are really close (certainly as is the case at the LHC) then they can see one another's quarks. A neutron is overall neutral but it still have very weak EM properties because it's got 3 charges inside it, it's a tripole. As such there will be very slight EM corrections to all of this stuff but it'll be small compared to the Yukawa dynamics.

@1st block
I do read about the strong force and know the difference between the nuclear force and it (First encounted that in the http://en.wikipedia.org/wiki/Strong_interaction where there is a nice animation illustrating the process. Before that I have absolutely no idea what mediate tha nuclear force, despite I have already breifly being introduced strong interaction from some pop science source and science magazines).

I also google searched many edu website (one is a brief pdf lecture on gluons)
http://rjs.phys.uvic.ca/sites/rjs.phys.uvic.ca/files/lec13.pdf
Though I must admit I did not understand much as I still have not learnt the maths yet. However that source is sufficient to tell me that gluons tend to bound together due to themselves carry the color charge, hence explaining why the strong force has such a short range despite the masslessness of gluons

@2nd block
Soime of my high school chemistry books (specifically in the chapter of nuclear decay and reactions) have introduce what you mentioned in this block (although they used the more easily understood term "nuclear force"). I was not surprised until the bolded portion. A brief search from wikipedia
http://en.wikipedia.org/wiki/Tritium
said tritium decay via beta decay (which is something related to the weak force)
I did heard about Yukawa force and Yukawa potential (while I was browsing particles in wikipedia) but I understand nothing from them except they have something to do with the strong force

@ 3rd block
Initially I have considered about the neutron still have electric charges despite it is neutral, thus can still somehow interact with protons. However I have second thoughts after remembering that neutrons are quantum objects thus I think it cannot be polarized like classical metal spheres via electrostatic induction

Your explanation helped clarify it


4. Although you can write such a process as p+e \to n (up to a neutrino) what really happens is generally the proton decays into a neutron and spits out a positron. Then the positron ends up hitting an electron. Electron capture can occur but it's less straight forward because you need a huge bath of electrons to drive the process. A proton with too much energy can spit out a positron (and electron neutrino) all by itself.

You should bear in mind that for these sorts of processes the specific quantitative stuff is very difficult to compute. What holds nucleons together is the residual Yukawa force of the strong force. What pushes them apart is both the Yukawa and EM force. And what causes protons and neutrons to turn into one another is the electroweak force. There's all sorts of non-perturbative effects and electroweak corrections and Yukawa limits flying around the calculations, much of which we're only just beginning to do on supercomputers you could chock an elephant with (please, no one chock an elephant with a computer). In principle any one of the possible transitions we're talking about can occur. The sticking point is how often they occur relative to one another, what conditions they prefer or create and how stable are the results.

What precisely are you needing this information for in regards to scifi?
@1st block
The part about electron capture is now clarified, thanks!
From my high school chemistry and physics textbooks, they mentioned the beta- decay more often. In fact before I went to uni prepardatory course last year, I never know beta+ decay exist (this is because before that period during my browsing for particles in wikipedia driven by boredom I came across the proton decay of GUT. Due to my limited understanding I though the proton cannot decay, thus I was shocked when I first heard of beta+)

Also wikipedia and some other sources also mentioned the proton is lighter than the neutron thus won't a neutron beta- decay be more energy favourable hence more common?

@2nd block
I agree with the last part of the sentense
For other portions, because I have no idea what Yukawa force is I cannot give any comment (I'm only slightly more familar with the weak force (that the w and z bosons mediates it. When a up type quark emits a W+ it turns into a down type quark. The W+, being massive is unstable and decays weakly into positron and anti electronneutrino) and strong force (which both a phd at uni and cptbork in the "like charges repel" thread have explained to me that it is many times complicated than what I think, it is not really correct to say which color attracts what). I end up confused when I read about the quantum aspect of the Electromagnetic force other than I know the photon mediates it. I also have an habit of treating the EM force classically. As for gravity, I'm still trying to work out relativity thus don't understand much except that c is constant for all frames of reference, gravity is a result of spacetime curvature by massive objects. I briefly learnt about the Rimenian metric tensor from Michio Kaku's Hyperspace).

(Hopefully this will give you an idea of my particle physics knowledge pool, which is quite limited (and I lernt most of them from wikipedia and sciencemagazines such as newscientist and scientific american). However it is expected to be slowly increasing as I progress up the uni)

@3rd block
Warning potentially crank stuff below, please proceed with extreme critical mind
The origin of this thread, the "like charge repel" thread, "CP violation imply T violation" thread, "positron muon annihilation possible?" thread is the below link

http://secretuniverse.wikia.com/wiki/Negative_mass

The "clumping problem" arise when I found that like charge attract and unlike charges repel from the equations (manipulated with the - sign) for a hypothetical negative mass where all 3 types of mass are negative (as according to wikipedia, this is necessary to conserve momentum and to allow relativity to remain valid in the scenario) and the lowest energy state of those universes are based on magnitude not direction

This means, if I tried to make a hypothetical negative mass atom, the usual proton-electron won't work. Instead I need to use proton-positron. However these lead to 2 consequence
1. All stable negative atoms must be charged (since unlike charges repel, thus there is not way to make it neutral. In addition, you won't call a cluster of neutron an atom do you? Neutrinos (which are the only known neutral leptons) don't work simply they are too weak to form an atom with other particles)
2. Since like charge attract, that means any two like charged negative atoms will be attracted (the attractive force is the combination of the proton AND the positron). In the ordinary matter case, first there is those quantized orbitals to prevent an electron from spiraling into the nucleus and the nucleons will repel each other (electrons also repel each other), thus balancing out the attraction and from stable molecules or ions. However in the negative mass case, based on those equations, there is nothing to balance out the attraction between nuclei (there is only attractive, no repulsion between the like charged negative atoms) The consequence of this is the nuclei will soon hit (The electrons are not an issue as they are still being kept ahead from the nucleus using the orbitals). Then the question arise on whether they will fuse once they touch each other cause if they do that means my whole settings for negative elements will crumble and I have to find alternate ways to get around it. It will also mean negative atoms fuse many orders of magnitude easier than ordinary atoms (IMO I think this is ridiculous)

The find out whether they will fuse on contact. I then think of the closest reality case to my scenario. Eventually the proton-neutron fusion idea popped out of my head and this marks the creation of this thread (A side effect of this idea is that this might be a way out of the technical problems regarding fusion)

In short. The information of this thread will act as a toy model to help me determine how to solve the "clumping problem" of my scifi negative mass

Some intro of me doing scifi:
First, to get some scifi ideas, I have a habit of manipulating, switching signs, swapping terms etc. of maths equations and quantities and see what it turns up. (My most usual method is to add a - sign whenever possible and interpret its physical implications)
e.g. The "dark emitters is it possible?" thread is a result when I try to plug a - sign into the quantity known as luminous intensity
e.g.2. When I add a -sign to mass and wikipedia it, this is how I first got introduced of the highly speculative term known as negative mass

However, because I like truth and hate lies. I will try to find out whether my manipulations is actually possible using known laws of physics. If it is found out to be forbidden, I usually discard the idea unless it is extremely crucial to the plot. Hence the appearance of the "cold flame" thread, the "dark emitters" thread, the "divison by zero, seems flawed" thread (In fact in the past I also discuss similar ideas with my peers and teachers, which there is mixed response)

Because I have seen so many news of scifi stuff have been realise or close to realise (e.g. invisibility cloak). The reason of making my scifi as scientifically accurate as possible is because of * and also because I will actually planned to carry out expts on them when given the chance. IMO the joy of bringing an idea to reality is very large. In other words, my scifi is actually an expt plan of all the wild ideas I came up from my mind and see whether one day I can realise them or prove that they are 100% impossible

*I'm really fed up with plot holes, inconsistencies in scifi, which is often resulted from technobabble (introducing a term which sound technically but actually does not carry any meaning, star trek being the best exmaple of these) or because they have not treat the science aspect seriously (e.g. the problem of entropy in the ontological paradox of time travel, how the unusual properties of a scifi substance arise, the physics behind hyperspace travel etc.). If I build my scifi from bottom up (from the particles to the multiverse) and ensure all of my equations make sense. Then the self consistency of the settings will ensure there are minimal or no plotholes

Since you numbers your questions I'll just number my answers....

1. Yes, though how close depends on the nucleons. p+p \to D + \ldots is possible, it's one of the steps in building up the higher elements from just Hydrogen. If it didn't work we wouldn't exist. But that doesn't mean it's easy. The Sun is mostly free protons by mass (the free electrons which partner them as 1/2000 the mass) and despite the core being 15 million Kelvin and many times denser than Lead the average proton will bounce around for billions of years before having another collision with a proton which is close enough to precisely head on, at high enough energy, that they'll fuse into Deuterium. Fortunately there's a lot of protons in the Sun so statistically billions of tons of them manage it every second (releasing millions of tons of energy).

n-n I'd almost expect to be easier, since they don't repel one another. However, neutrons decay with a half life of 11 minutes when not bound with something else so they won't last long. Outside of very very rare instances or artificially orchestrated setups like we make in experiments I doubt this is a main channel for any processes.

p-n collisions will be many orders of magnitude more likely, since each neutron will have many protons around it and there's still no repulsion between them so if Deuterium is energetically favourable to separate p and n I imagine this will happen quite a lot in a star, which brings us to question 2.

2. I'm not familiar enough with this stuff to know the numbers off the top of my head but I would have thought so, else Deuterium would decay because it would be energetically favourable. Tritium is unstable and has a half life in the years (a decade or so?) but Deuterium is considered completely stable.

3. If there's 2 possible forces involved and one of them isn't how do you reach the conclusion no energy is involved? What about the strong force? Nucleon interactions aren't governed by gluon interactions, which is what the strong force is. They are governed by meson interactions giving rise to a Yukawa force, an effective field theory (http://en.wikipedia.org/wiki/Effective_field_theory) for QCD.

The Yukawa force is stronger than the EM force, though not as strong as the strong force. Nucleons will only see their neighbours via the Yukawa force but protons will see all the protons in the nucleus because the EM force is longer range. This is why trans-Lead elements are unstable, there's so many protons all pushing one another that the neighbour to neighbour Yukawa attraction can't hold it together forever. However, in the case of something like Tritium, where there's no real EM repulsion, the instability is Yukawa force related.

It is worth pointing out that when nucleons are really close (certainly as is the case at the LHC) then they can see one another's quarks. A neutron is overall neutral but it still have very weak EM properties because it's got 3 charges inside it, it's a tripole. As such there will be very slight EM corrections to all of this stuff but it'll be small compared to the Yukawa dynamics.

4. Although you can write such a process as p+e \to n (up to a neutrino) what really happens is generally the proton decays into a neutron and spits out a positron. Then the positron ends up hitting an electron. Electron capture can occur but it's less straight forward because you need a huge bath of electrons to drive the process. A proton with too much energy can spit out a positron (and electron neutrino) all by itself.

You should bear in mind that for these sorts of processes the specific quantitative stuff is very difficult to compute. What holds nucleons together is the residual Yukawa force of the strong force. What pushes them apart is both the Yukawa and EM force. And what causes protons and neutrons to turn into one another is the electroweak force. There's all sorts of non-perturbative effects and electroweak corrections and Yukawa limits flying around the calculations, much of which we're only just beginning to do on supercomputers you could chock an elephant with (please, no one chock an elephant with a computer). In principle any one of the possible transitions we're talking about can occur. The sticking point is how often they occur relative to one another, what conditions they prefer or create and how stable are the results.

What precisely are you needing this information for in regards to scifi?

Thanks for your informative explanations.