What forces are at work when neutrons are ejected?

It may be difficult to separate "theory" from "application," but let''s see if this helps facilitate the discussion.
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Chris Bradley
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Re: What forces are at work when neutrons are ejected?

Post by Chris Bradley »

Just to mention - having initiated the thread to see if folks wanted to offer Steven an answer to his original question (as it was already a thread-drift elsewhere), I'd say the matter has now been answered in a few different ways, qualitatively and qualitatively, and we seem to have now exhausted the possible suggestions people want to make.

Of course it's likely that we'll never know for sure. Maybe it is too 'fundamental' for us to ever tease apart, or maybe we will tease it apart one day. Who can say? In any case, I had just wondered if folks had thought on it before.

'The Uncertainty Principle' is a different topic - it may be necessary to mention it as part of an answer to the question, but I think that's been done now.

'People's personal interpretation of "The Uncertainty Principle"' is a yet further topic, so is definitely a thread drift.

Thanks.
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Richard Hull
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Re: What forces are at work when neutrons are ejected?

Post by Richard Hull »

Hate to go against convention but no one has yet convinced me that a neutron is a particle, existing as such, within the nucleus! (I am certainly open to the idea though)

Anyone been in a nucleus?

The neutron is obviously an extra nuclear particle. We see it exit bulk matter. We can track it and know that it is highly unstable with a relatively short half life in the wild.

Would it be beyond the pale to suggest that it is a nuclear condensate?..... That certain nuclear conditions or instabilities cause it to form suddenly at the edge of the nuclear influence?

We base all of our intra-nuclear knowledge on a framework of guesses and carefully crafted, testable assumptions that work for us and have satisfied and gratify us. I am thinking that the nucleus cares little for what we think or our machinations. We are comfortable with our explanations for the unseeable and unmeasurable within an edifice whose door is forever closed to us. We only see what is dumped as trash or the debris from our frustrated efforts to go inside by blowing the place to bits and assume the debris has meaning. ( A decent assumption, I guess)

We may be too clever by half and may never know the reality of it all.... If there is any at that level.

Just looking for flies in the ointment.

Richard Hull

I have lived with and accepted that the neutron has life in the nucleus. Do not get me wrong here. someone has got to work in gravity boots or be the Devil's advocate, I guess. RH
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Chris Bradley
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Re: What forces are at work when neutrons are ejected?

Post by Chris Bradley »

> Hate to go against convention but no one has yet convinced me that a neutron is a particle, existing as such, within the nucleus! (I am certainly open to the idea though)
I'd point to activation, one that you have done many times yourself, as the experiment that could provide the answer here: If the neutron does not stay as a neutron when it mixes in with a nucleus, then wouldn't we observe prompt beta emissions *during* neutron absorption into a nucleus, rather than sometime *after*?
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Richard Hull
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Re: What forces are at work when neutrons are ejected?

Post by Richard Hull »

Why should we observe that? (instant beta emission) Because it doesn't fit our theories? Not good enough for me. We have no idea what happens to macro forces in a nucleus. We do make assumptions that they are unchanged, but dream up new forces, both strong and weak to explain away issues based on conteracting the macro extra nuclear forces.

As for beta emission....Another matter entirely! As the balancing act in this process never works out to simple theory, we invent another particle intrinsically massless and, naturally undetectable in any specific beta decay event, but with a kinetic energy that magically rebalances all our probs away. Self consistency retained and testable only over quadrillions of events assumed to be part of past decay events in a vast sea of nuclear events. Good enough for theoretical science and it stands as fact for many. (most)

I have always noted that the neutron decay to a proton and electron, (which are the only actual things ever detected in such decays), might, oddly enough, be what the neutron is composed of, but then there is the retort about spin and magnetic moments, quark balancing, etc., I am told on good authority, kill that concept. Well can't I kill the idea of the neutron being part of an atom? No that is not even to be considered. Give me a break. The neutron in the atom is a must have to make theory work and solve nuclear beta decay issues.

I would be happy with a nucleus of protons and electrons only allowing for but one force that defeats all others and is itself manifested as a variable mass that readily exchanges itself according to a new set of internalized nuclear rules I can't fathom. Certainly better, ocama's razor wise, than a zoo and several extra forces. All other ephemeral particles from neutrons to mesons to quarks can be explained as evaporations from nuclear events so intense and local that different forces and particles exist only in that fleeting environment, but not in the averaged out, current matter/energy cosmic situation. They are not part of the nucleus. They are part of a long dead past belched up from the dead.

Whatever we invent, it is always self-consistent and testable. We call it science because it is all we have to ward off religious dogma and old fashioned superstition. One man's religion is often another man's heresy. Science should not be left out of that mix especially if it starts to tell of things unseen, but imagined even if guided by self consitent theory and is testable. It makes those of us who don't like the other dogmas and disconcerting unknowns feel like we are on solid ground.

For most here, if we are without science, we are truly adrift. I will only let science take me so far afield before I feel a cold breeze up me kilt.

Richard Hull

Why don't neutron stars decay in a few minutes to an hour? Or, in that decay, reform their mass into hydrogen (electron and proton) once clear of the energetic star? Some kind of unknown binding on a scale that is macro, but resembles a nuclear force? Gravity should not slow down decay, or should it? Time dialated decay? RH Too many questions and no good answers.
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Re: What forces are at work when neutrons are ejected?

Post by Steven Sesselmann »

Richard,

I have been following this tread, but as I had nothing intelligent to contribute, I stayed out of it. What puzzled my mind was the forces are at play, what causes a neutron to be ejected with 2.4 Mev energy? Not so much where the energy comes from, but what the nature of the force is.

Could it be,

a) ...centripetal force, ie the nuclei spiral rapidly inwards until one particle lets go?

b) ...the neutron is composite and made up from a proton and an electron, where there is a small probability that the electron finds itself on the far side, thereby leaving the two positive faces in contact.?

c) ...thermal energy of the neutron at room temperature being 2.4 Mev higher than the ultra cold state of being in the nucleus.

d) ...that the neutron doesn't move at all, and that we the observers move through time at a relatively different rate than a sub atomic particle, thereby giving us impression that the particle is moving.

Food for thought...

Steven
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Re: What forces are at work when neutrons are ejected?

Post by Dennis P Brown »

I answered the question on the energy of the neutron 'ejected' from the nucleus very clearly far up in this thread. Whether one wants to believe scientific fact (and that does not mean something else isn't causing the process, only that is how science works) or just go off into speculation is fine. But the answer does not require a force - no more than a photon needs a force to start at the speed of light - that is just as 'counter intuitive’ as the neutron issue yet no one here is asking how that is possible.

So, once more I will answer a question using accepted science which will run against the grain ... but a neutron star does not decay in fifteen minutes for the same reason a neutron does not decay in a nucleus - it is less stable if it decays than if it remains a neutron. A neutron lowers its energy when it is bound. The only way to confirm this is to calculate the energy in each case - trying to use a easy to understand example in our macro world just will not cut it for quantum effects. Can't get around that.
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Re: What forces are at work when neutrons are ejected?

Post by Jeff Robertson »

Another thing to keep in mind when discussing nuclear-related topics such as this is that "force" is a very classical, borderline obsolete term. While it may be appropriate to talk of forces on a macro scale, the concept of forces (in the sense that particles are "pushing" or "pulling" on each other) holds no meaning on the nuclear level (or in the quantum world at all, for that matter). Modern quantum field theory (and most modern quantum theories) states that these "forces" are really the exchange of particles carrying momentum/energy. For the electromagnetic force this is the well known photon, for the strong interaction this is the gluon, and the weak interaction is governed by the exchange of W and Z bosons (some versions of quantum field theory predict an analogous particle for gravity called the "graviton," although gravity is such a small force in comparison that it would be nearly impossible to detect said particle).

That said, if you're trying to explain neutron emission in terms of some force pushing or pulling the neutron out of the atom, you may be left feeling unsatisfied. In fact, if you're trying to reconcile a neutron's behavior with any sort of classical concept of motion or dynamics, chances are good your answer is either wrong or incomplete. Steve's ideas are interesting to think about, but with all the success quantum mechanics has had in explaining subatomic particles, I doubt that neutron behavior can be fully explained with such archaic concepts (although they could very well play a part, this is all just speculation after all).

While I'm more inclined to believe the solutions Dennis or myself proposed (since quantum has been the most successful theory on the nuclear scale to date), I agree with Richard's notion of playing devil's advocate. We can't assume we "know" anything about the neutron. We know nothing for certain about its shape, size, constituents, or behavior. We can't even observe a neutron directly (have you seen a neutron before? because I haven't!), we can only observe its effects on the environment and infer that a neutron must be in play.

All of that said, I'm still a fan of my energy balance proposal . Within every particle there is an internal tug-o-war between the particle's kinetic/thermal energy and the potential energy due to surrounding particles. If the kinetic energy is greater then the particle is free to roam; if the potential energy is greater, then the particle is bound to the system (this is one of the reasons why planets orbit around the sun, and electrons are bound to nuclei). This is how plasma is formed - we give enough energy to the atoms until the nuclei and electrons break free from each other, resulting in a "soup" of ions and electrons freely roaming. Energy conservation is one of the few physics concepts that has survived from classical mechanics all the way through modern quantum theory.

When a neutron is bound to the nucleus, it means that its potential energy due to the strong force is stronger than its internal energy. When some event, such as the collision of an additional neutron with the nucleus, shifts the atom, the neutron is pushed out of equilibrium for a moment. If this shift causes the neutron to temporarily lose enough potential energy so that it drops below its internal energy, the neutron will be able to break free from the nucleus. If it is not enough to upset the neutron's balance, then it'll simply settle back down into equilibrium. These are just my thoughts at least.

Apologies for the long post, this always seems to happen when I start talking about quantum!

Jeff
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Re: What forces are at work when neutrons are ejected?

Post by Frank Sanns »

Jeff Robertson wrote:


> While I'm more inclined to believe the solutions xxxxx or myself proposed (since quantum has been the most successful theory on the nuclear scale to date), I agree with Richard's notion of playing devil's advocate. We can't assume we "know" anything about the neutron. We know nothing for certain about its shape, size, constituents, or behavior. We can't even observe a neutron directly (have you seen a neutron before? because I haven't!), we can only observe its effects on the environment and infer that a neutron must be in play.

Neutrons have no external electric charge so they should and do pass right though solid objects. It is the Coulomb force that keeps normal matter looking and acting the way it macroscopically does. Similarly a visible photon should not interact with a neutron both because of the wavelength of a visible photon would be too long and the lack of charge would make a neutron invisible. A neutron star then should be invisible or should I say transparent to visible light. Gravitational lensing would be expected though as the gravitational forces would still do their work.


> When a neutron is bound to the nucleus, it means that its potential energy due to the strong force is stronger than its internal energy. When some event, such as the collision of an additional neutron with the nucleus, shifts the atom, the neutron is pushed out of equilibrium for a moment. If this shift causes the neutron to temporarily lose enough potential energy so that it drops below its internal energy, the neutron will be able to break free from the nucleus. If it is not enough to upset the neutron's balance, then it'll simply settle back down into equilibrium. These are just my thoughts at least.
>

And what of anti color charge with neutrons? Anti electrical charge is easy to appreciate but when it involves the color charge, all bets are off. Anit matter has its own consequences and ramifications. Is this anti potential energy or positive potential energy or double potential energy? At high packing densities does degeneracy become equivalent to the environment in an atom or vice versa?

Frank Sanns
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We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
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Re: What forces are at work when neutrons are ejected?

Post by Jeff Robertson »

Well I was being facetious with my comment about not being able to "see" neutrons, perhaps I should have made it more obvious. Low energy photons do not interact with neutrons because, as you said, they're electrically neutral. The quarks that make up a neutron (for those who don't know, three "quarks" are what come together to form a neutron) do have electric charges, though, so I believe high energy photons do interact with the quarks inside a neutron. Not completely positive though (no pun intended), if anyone can verify this?

As for anti color charge, I'm not exactly sure what you're getting at. My understanding of anti particles is that they're identical except for having opposite spin and electric charge. If this is true, this would imply that the electromagnetic potential energy of an anti particle would have the opposite sign as the potential energy of its particle counterpart, which is what I think you were saying. The potential we've been talking about in this thread, though, is due to the strong interaction, and as far as I can tell the strong nuclear force interacts with matter and antimatter in the same way.

I'm rather rusty on quarks and all that fun stuff, so take everything I say with a grain of salt.

Jeff
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Re: What forces are at work when neutrons are ejected?

Post by Frank Sanns »

Jeff,

Quantum Chromo Dynamics (QCD) is just one of the many theories related to hadrons which of course includes quarks and obviously then neutrons and protons. I used it as an example because anti matter is not anti coulomb charge matter. Negative and positive electric charges neutralize but they do not annihilate like matter and anti matter (anti color charge). The color charge is an attribute just like a Coulomb charge but with quite different properties. Also spin or mass alone does not cause annihilation .

Quarks, which are the accepted building blocks of hadrons (protons and neutrons in the case of the original thread), have properties that include electric charge of -1/3 or +2/3, mass, spin, and color charge. It is this latter that is quite interesting in the stability or instability of quark composites like protons and neutrons. Call it whatever your will but what is referenced as color charge is what has a profound effect on stabilities, and reactivities. The attributes mentioned above are definitely the smoking gun of ejections from nuclei.

Frank Sanns
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We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
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Re: What forces are at work when neutrons are ejected?

Post by Dennis P Brown »

Understanding how neutrons are ejected by a 'force' or other cause from a nucleus is interesting speculation and I see this thread has provide the opportunity to 'fill in the theory you desire' here. Of course, appeal to alternate explanations is only speculation unless such an alternate theory provides a better - that is more accurate - calculation for the energy that is experimentally measured.

Hence, the basic idea of momentum and the uncertainty principle does provides both the reason and an accurate calculation of the kinetic energy of the neutron under these situations and this approach is the scientifically accepted method and provides the accepted explanation - until someone offers a more accurate calculation by offering a model that provides similar or better answers than they are just using speculation, not science. Readers need to understand the difference.

Aside: I do not wish to imply that speculation is not useful in science - it can be extremely useful besides being fun.
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Re: What forces are at work when neutrons are ejected?

Post by Richard Hull »

Jeff got my drift as devil's advocate in my post.

I might be classically educated, but I am not classically bound.

I understand that if one is gainfully employed in the world of physics one must spout the party line or face dire consequences. I have seen a number of retired physicists go rogue in their thinking, free at last of the peer pressure to muse openly.

For me, Quarks and all there colors and flavors, charms, etc are a joke we play on ourselves for balance sake in explaining physics to a level 4 layers below direct normal world laboratory observation. They are that which was and are no more.

If one is willing to apply big bang energies in the tiny space of a proton then you will see what was before protons and not the constituents of a proton. In the energy ball around this event what we see is stable for nanoseconds or less as the energy ball expands reverting the near big bang space back to 3 kelvins space. What we have recorded was a ghostly apparition, a resurrection, only to be returned to the grave from which it arose.

Richard Hull
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Re: What forces are at work when neutrons are ejected?

Post by Frank Sanns »

Richard, I am with you on this. That is why, while I listed spin and color, I only refer to them as attributes.

Spin, a misnomer that many students think is classical spin when in fact has nothing to do with classical rotation. Then there are fields. Yes those invisible yet powerful nothingnesses. Things leak to and from them but from where and by what mechanism. Does not work for me.

The world of the very small is where the real physics are, and not this macroscopic world that is simply a construct of the electrostatic forces. Things are not as they appear and by the time the mind is developed enough to go beyond, it has already been heavily jaded by what has been seen and learned, and experienced. Science has been stuck for a century, no doubt because of the jade.

Frank Sanns
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We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
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Re: What forces are at work when neutrons are ejected?

Post by Steven Sesselmann »

My 5 cents worth...

I go along with Richard's view, that these particle events create hot conditions similar to those that might have existed in the past, but where I beg to differ is that what we see has anything to do with the past.

To observe how these things looked in the past we would have to observe them from the past, which of course we can not. As observers we are observing the particle smash from ground potential, which is nothing at all like what the particles see.

A particle pair creation in the lab which for us lasts only nano seconds, may for the particles created, last an eternity.

Until we fully understand the observer dependency, we are never going to make sense of it.

In these CERN experiments we should not attempt to understand what we see, but instead we should model the whole event from the perspective of the particles, try to "be" the particle!

Then we will see that it looks a lot like our world, if not exactly like our world.

Remember how long it took before Copernicus unraveled the mystery of the planetary motions.

Steven
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Re: What forces are at work when neutrons are ejected?

Post by Jeff Robertson »

Side note, I was discussing this with an old professor of mine and he believes conservation of momentum is the only law needed to explain neutron ejection. Neutron comes in from the left, strikes the nucleus, knocks a neutron out from the right side. No need for any quantum voodoo or anything beyond classical mechanics.

It makes sense if you think about it. I mean, if a neutron strikes a nucleus then that momentum has to go somewhere right?

Jeff
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Re: What forces are at work when neutrons are ejected?

Post by Frank Sanns »

The original question on this thread is a bit ambiguous as a neutron is not ejected from a stable nucleus. The nucleus has to be unstable because of an unfavorable neutron to proton ratio or energy input from outside of the nucleus. Conservation of momentum alone can not account for the interactions within the nucleus from either situation. While the Fermi energy(Pauli Exclusion for fermions) and momentum transport may explain the rules, it says little about the inner mechanisms.

Frank Sanns
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We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
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