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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Frank Sanns
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Re: What forces are at work when neutrons are ejected?

Post by Frank Sanns » Thu Jun 28, 2012 1:03 am

The Uncertainty Principle is not something mystical or magical. It is not even unique to quantum mechanics. It is applicable to all forms of waves including those in the ocean and sound waves too. It simply is a relationship between trade offs. Usually is it measuring time and precision.

If there is a sound wave with 2 meter wavelength and you only measure for one tenth of the time that the wave goes by, they you will not have a very good estimate on the wavelength or the energy of the wave. If however, you measure for a long time for multiple waves to go by, then you will have a good estimate of the wavelength but it will have taken much more time. Nothing magical here. Just basic wave physics.

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

Post by Dennis P Brown » Thu Jun 28, 2012 9:57 am

No one has said the uncertainty principle is magical and please don't add such nonsense.

Also, the quantum uncertainty principle is not the same as what is used for uncertainty in measurement related to ocean waves - the quantum uncertainty principle puts absolute limits on what can ever be achieved with measurements, and relates this to Planck's constant.

Time does not enter into the measurement equation I gave for the uncertainty principle for position/momentum - what you are using is an invalid analogy. Of course if you limit a time dependent measurement in time, you introduce a finite and well determined error relative to wave position - this has no relevancy to the topic of the neutron energy when it is no longer bound within a nucleus - only quantum principles apply to this situation. Macro measurements based on Newtonian mechanics does not apply - this has been proven by experiment.

When one uses the uncertainty principle, and the standard Newtonian momentum/energy relation corrected for relativistic effects, the exact answer for the neutron KE is obtained for the now free neutron.

Continued arguments on this point are silly - if you desire to believe nonsense, that is your right. If you wish to try and disprove this scientific fact, I'll do my best to help you with your ideas and experiments but if you just want to continue to make verbal arguments, you are wasting everyone's time.

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

Post by Jeff Robertson » Thu Jun 28, 2012 11:00 am

Hey Dennis,

I know the uncertainty principle very well, and like Frank says (although wrong context) it is not limited to just Heisenberg's famous equation. The formal mathematical model of quantum mechanics contains a famous equation which relates the uncertainty between any two observables. The famous uncertainty principle which you used is just one application of this generalized uncertainty equation, when applied to position and momentum. The "delta x" and "delta p" in Heisenberg's uncertainty principle do in fact represent standard deviations. Not deviations in human error or measurement, as you said, but in the fundamental observables of the particle in question.

I do, in fact, remember the electro-static force between an electron and proton (can't tell if that was intended to be condescending or rhetorical, I'll assume rhetorical). What keeps the electron from spiraling into the nucleus, at least the way I learned it, is the quantization of the electron's angular momentum, which is derived from the wave function of the hydrogen atom. The electron can only take on certain values of angular momentum which are multiples of the reduced planck's constant (excluding the 1/2 spin of the electron itself). Without this quantum law, the electron would radiate as it orbited around the nucleus (as it's constantly accelerating), spiraling down until it collides with the proton. I'm not sure how Heisenberg's uncertainty principle applies to the electron's stable orbit, that's something I'll have to think about. I suppose as the electron travels closer to the nucleus it becomes more defined in its position (as it is stuck in a potential well and there is a less broad region in which it is likely to be), implying a greater uncertainty in the momentum, but I see this as merely a consequence of the wave equation rather than the governing law itself. The quantization of angular momentum is what I learned to be the main governing law which keeps the electron and proton from colliding. An electron's wave function must be in compliance with Schrodinger's equation, and it so happens that virtually every possible solution of the Schrodinger equation for the hydrogen atom allow only discrete values for the electron's angular momentum.

And in the last section of your post, you justify your method of analysis by saying "well, my numbers were close enough." Just because your numbers are in the ballpark of what they should be does not mean you conducted a proper analysis, that's the ends justifying the means. They weren't even in the ballpark at that - you made some comment about neglecting relativity to justify bumping it up an order of magnitude. You act like I'm insinuating that every other physicist is wrong and I think I have discovered the new standard model, when really I just didn't agree with what you did. I'll read up on this tomorrow, it's very possible that I'm just flat out wrong. If your analysis was in fact correct then I'll own up to it, but it doesn't make any of my other points any less valid. My only criticism of your analysis was that the momentum term in the uncertainty principle relates to the standard deviation, rather than the momentum of the particle itself.

In response to what Frank said, the uncertainty principle is an entire different phenomena than what goes on in macroscopic waves (as Dennis said). All quantum mechanic uncertainty principles are derived from the fundamental probabilistic nature of the wave function, which has no analogy towards the macroscopic world. Any uncertainty which exists on a macroscopic level is due entirely to experimental limitations or human error. That said, whether on purpose or accident, Frank stumbled upon an additional uncertainty principle. His analogy to measuring energy and time wasn't invalid at all, in fact it is an actual equation which is perfectly analogous to Heisenberg's uncertainty principle. That is, (delta E)*(delta t) must be greater than or equal to one half the reduced planck constant. This comes directly from the generalized uncertainty principle.

I'm not sure why you're getting so unnecessarily defensive and snippy. This forum is intended to be an open discussion board for ideas and to talk about various physics topics. Frank is not "wasting everyone's time" as you said, he's participating in an intellectual discussion about the underlying physics of nuclear decay. You come across as having a sense of elitism, when in fact you are not the only one who has knowledge on this topic. Telling people they are wasting everyone's time by posting, saying what they believe is nonsense, and that disagreeing with what you say is on par with trying to disprove scientific fact. Your past couple responses seem a touch pompous and just downright impolite. Whether or not someone's thoughts are accurate or not does not give you the right to have such a toxic attitude.

That said, there are some interesting things to think about here. I think tomorrow I'm going to dust off a couple textbooks and read up on some applications of the uncertainty principle.

Cheers,
Jeff

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

Post by Frank Sanns » Fri Jun 29, 2012 2:02 am

Collapse of a wave function because of observation for example is different than the probability statistics and the uncertainty. The wave function in quantum mechanics is not the same as waves in the ocean as it describes a probability whose form is a wavelike function. However, the Hamiltonian operator (potential and kinetic energies) in the Schroedinger is precisely derived from waves in the ocean. William Hamilton back in the mid 1800s envisioned a planet flooded with water. He imagined what a wave would be like when it passed by its point of origin. Soon it was clear to him that only certain allowed energies (wavelengths) were allowed (constructive interference) while others would not be allowed (destructive interference) as they would quickly die out.

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

Post by Dennis P Brown » Fri Jun 29, 2012 4:55 pm

Jeff,

first off I never said (and this is what you wrote that I said)

"deviations in human error or measurement, as you said, but in the fundamental observable of the particle in question."

I, in fact, said the exact opposite of what you are writing here. I most certainly did point out that the uncertainty principle is not a measure of measurement errors, but an absoult limit on a quatum system.

Also, I did not say my answer was close enough - I carefully pointed out that my approach must be corrected for relativistic effects to get the correct answer.

So here is exactly what I said:

"A rough calculation I did puts it at about 0.1 MeV; this is not corrected for relativistic velocity effects (big effect at these energies) so this value is too low - just as it appears to be - so the real answer would be more like a few MeV. Still, this simple approach shows that the energy of confinement is huge so a neutron (no longer bound by the strong force (read gluon force)) would have a huge KE outside the nucleus."

Note the word 'rough calculation'. And I point out it is not corrected for relativistic effects. Further, at no point and no where did I say my answer was good enough nor even implied that.

Gotta read the post to be accurate Jeff.

I also did add that the other quantum numbers for the electron bound within an atom do in fact come into play but realized this would further confuse someone struggling to understand the uncertainty principle. Glad you decided to expand on that topic but don't imply that I didn't consider this or somehow mised it.

I too have calculated the electron orbits in hydrogen and yes, the other quantum numbers are critical. Also, the orbits are the only solutions. That all said, you really think that will explain the question about why Frank's approch was incorrect? The uncertainty principle does have a factor in this and is a clearer way to explain the issue to him. Maybe not but that is a judgement call. Still, a full hydrogen atom solution would not be helpfull at all.

Relative to the issue of a neutron having KE after leaving the nucleus and why an electron cannot be in a space the size of a nucleus, the uncertainty principle does have a major impact on whether an electron can approch/occupy that volume - do the calculation (and more to the point, most people here can do that calculation using very simple math - that is why I used that example, by the way.)

Yes, spin has a major impact but again, if you notice, the people were just trying to understand why a neutron is 'ejected' with such energy. Your current example does not address this point about the KE of a neutron leaving the atom - my use of the uncertainty principle does and is correct. Frank added a rather simple counter example and I was showing him (without a full blown quantum calculation) that his idea does not work and why. Yes, too simple for people whho have done the real solution of a hydrogen atom. Do you think that would have help Frank understand the error of his counter example?

Jeff, I most certainly did not get "unnecessarily defensive and snippy. " I was polite in my repose after being told by Frank "thread rambles much deeper into conjecture". All I did was point out I used accurate physics. What is defensive about stating a fact?

Or are you referring to when Frank said "Certainty Principle is not something mystical or magical."

This statement is very disrespectful to me and my post and all I answered was "No one has said the uncertainty principle is magical and please don't add such nonsense."

Using the statement 'mystical or magical' relative to my post on a topic that is solid and well know physics was in fact very inappropriate and, frankly, disrespectful to me. So please Jeff, explain where I was silly?

Later I did notice that this thread was continuing to have people add rather far-out attempts to explain away a very simple, straight forward physics concept. Yes, the thread was getting silly and that was said more in jest, but this was true. I will not give the exact example of why I said that because if you read some of the posts, it was not an unreasonable statement. I will not point out its cause out of respect for the poster's honest mistake.

Your knowledge on the subject is obviously good, but others are not so well schooled and I used solid, simple answers to a very good question. Further, I was respectful and handled my posts in a professional manner especially after being told that I was somehow implying that a very clear physics concept was magical - please, my answer to that statement was fully appropiate.

As for the forum, I was in fact doing exactly what it is for - answering an excellent scientific question with well known science. I treated the subject in a manner that I hoped was clear. Please refrain from such incorrect and baseless statements relative to my posts.

Thanks

Aside: your last post, except for the points I don't agree with about my posts, is an excellent explaination and I am glad you added that.

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

Post by Chris Bradley » Fri Jun 29, 2012 5:15 pm

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

Post by Richard Hull » Mon Jul 02, 2012 3:34 pm

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

Post by Chris Bradley » Mon Jul 02, 2012 4:58 pm

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

Post by Richard Hull » Mon Jul 02, 2012 5:40 pm

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 » Tue Jul 03, 2012 1:23 am

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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