Misplaced Pages

Revision as of 17:05, 23 June 2009

Physics Stub‑class

This article is within the scope of WikiProject Physics, a collaborative effort to improve the coverage of Physics on Misplaced Pages. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.PhysicsWikipedia:WikiProject PhysicsTemplate:WikiProject Physicsphysics Stub This article has been rated as Stub-class on Misplaced Pages's content assessment scale. ??? This article has not yet received a rating on the project's importance scale.

oppenheimer-phillips process

Cleaning up the article

User:Enric Naval discovered some problems with this article and tried to clean it up, but it's clear he doesn't understand the nuclear physics, I cleaned it up so that the explanation would not only be clear to a lay reader, I hope, but also accurate. He has undone much of this, re-adding errors, massively. While I'm certainly not an expert, I've been studying nuclear physics since about 1954, when I was ten years old, and I thought for a long time I would be a nuclear physicist; I went to Caltech and sat through the Richard P. Feynman lectures that became the well-known textbook. So I have a general background, and the article, as edited by Enric, was, unfortunately, really poor, with blatant errors. There are so many I hardly know where to begin, but I'll start by asking Enric to slow down. The article as I left it was reasonably accurate; it might have some errors in it, but, to point to the dimensions of the problem, take the first sentence in Enric's version, bolding added:

This effect is thought to be caused by the combination of the acceleration of the deuteron, the Coulomb barrier of the heavy nucleus that the deuteron is approaching at high speed, and the great distance between the two molecules of the deuteron.

The deuteron is not accelerating, it is merely a high-energy deuteron. In the experiment involved, it has been given that energy by a particle accelerator, but it could, for example, merely be hot (very hot!), or it could be the heavy nucleus that has been given high velocity. It is the kinetic energy of the deuteron, relative to the heavy nucleus, that is relevant. Acceleration is mere history and is no longer relevant.

Secondly, "Coulomb barrier" is a term Enric is familiar with from Cold fusion; it refers to what makes fusion not take place, ordinarily, except at high energies. The Coulomb barrier is not a physical thing, it is not a general term used for electrostatic repulsion, the repulsion between two particles or objects with the same charge. Another name for the field behind this force is "Coulomb field." The term "Coulomb barrier" is not in the source Enric is following.

So the "Coulomb barrier" is not a property of the heavy nucleus, it is, rather, an effect that results jointly from the positive charge of the nucleus and the positive charge of the deuteron, and that positive charge is a property of the proton, and not of the neutron, so the proton is repelled, but the neutron is not. This creates a stress on the deuteron, which stress is resisted by its binding energy.

And then, worst of all, the deuteron is not composed of molecules. It is the nucleus of a deuterium atom, stripped of the electron. Nuclei, except for the basic hydrogen nucleus, which is a bare proton, are composed of quarks, but these quarks are organized or conceptualized into the older known fundamental particles: protons and neutrons. These are subatomic particles, not molecules, which are full atoms that have been chemically bound, through electron sharing.

And that's just the first sentence. Enric, I did know what I was doing when I edited this article, so I'm asking you to revert to my version, and we can then discuss what's not clear to you. Your version is far too mangled to correct one piece at a time. If we can't agree, I'll arrange that we have a diff that shows the difference, so that we can solicit some expert opinion. --Abd (talk) 16:34, 18 June 2009 (UTC)

I found a more detailed descriptoin of the O-P process

gives a different explanation than the one I used in the article. It apparently reports details from the original Oppenheimer-Phillips paper, which could go into the article. Don't know if the paper hosted by uiuc.edu would be considered RS, probably not. I suggest this text:

The process was discovered through deuteron bombardment of bismuth-209, which became radioactive bismuth-210, instead of the reaction expected from direct fusion of the deuterons with bismuth, to a compound nucleus, which would have generated neutron radiation.

--Abd (talk) 03:13, 22 June 2009 (UTC)

Made a fix

This edit elucidates some points that were perhaps unintentionally obfuscated. ScienceApologist (talk) 14:02, 22 June 2009 (UTC)

This edit was fine. What followed is a bit more involved. --Abd (talk) 14:41, 22 June 2009 (UTC)

Clarity and other issues

This diff shows what I did to clear up some problems in wording. For example, please do not use the term "deceleration", as the term is ambiguous. ScienceApologist (talk) 14:33, 22 June 2009 (UTC)

I can see this is going to take some work, with quite a few details to be discussed. Please don't make massive changes to the overall article at this point, but one at a time so we can agree on part even if we disagree on part. There is a fundamental issue to be resolved. Both Enric Naval's version and my version were based on a model of the process where the proton does not join in the fusion, except transiently (i.e., the neutron is captured, so you could consider the whole deuteron "stuck" to the nucleus, but the proton is still repelled strongly by the Coulomb barrier and is thus ejected.) SA, can you show better source on this? I did find a paper by someone who has published in the field, it's cited above. The whole point of the O-P process is that complete fusion doesn't occur; if it occurred, the reaction would be different, with a neutron being emitted instead of a proton. --Abd (talk) 14:39, 22 June 2009 (UTC)

Your understanding as you outline it here is correct, but the wording in the article implied something slightly different. The best sources on this are texts. This one is one of my favorites. ScienceApologist (talk) 15:27, 22 June 2009 (UTC)

There is some problem with this "complete fusion" term that you are outlining. There really is no distinction that is made. The O-P process is only relevant when deuterated nuclei are impossible but neutron-additional nuclei are (at least marginally) stable. I hope you understand. ScienceApologist (talk) 15:38, 22 June 2009 (UTC)

Color me unconvinced. And that's the point. Let me assume that you are more familiar with this topic than I. You haven't explained it to me, then, through your edits to the article or here, such that it's clear to me where we differ. Believe me, if I don't understand, we might create text that will make a reader with less background think that they understand, but they won't. We see that with Enric here, who did read textbooks, two of them.

This will be a bit long. To any reader without the patience to read this, please note: this is, for me, essential to editing this article. It may not be essential for you, nobody will be held responsible for "failure" to read this.

I often write in assertive style. This is the statement of a student, asked to explain in the presence of teachers how he understands the matter, and I am always aware that people with much more knowledge than I will read it. Simply that I assert something does not mean that I "believe" it, rather, I'm trying to express what I understand. If I don't understand, I guarantee you, there will be many others who will likewise not understand, and my "mistakes" will help us all to learn, perhaps the expert will explain better and the matter will become clear to the rest of us.

The only fusion that takes place in the O-P process, as far as I've been able to find from the sources, is a neutron fusing with a target nucleus. It's called a "strip reaction" because the neutron is stripped away from the proton. Now, if we simply arrange for energetic neutrons to bombard the target, with the velocity of these deuterons, they will mostly bounce, for in order to fuse, they must lose energy; in a nuclear reactor, they lose their energy to a moderator, which, through a series of recoils or other interactions, reduces them to the energy of thermal neutrons, which will fuse much more readily.

What happens in this process is that the neutron is bound to a proton. The momentum of this deuteron carries the combination close to the target nucleus; this is where deacceleration is involved. Both the neutron and the proton lose energy to the potential energy of the proton in the electrostatic field. Until the electrostatic force approaches the strong nuclear force that binds the proton and neutron together, we could think of the deuteron as a double-weight proton. We can see in this two complementary effects: the neutron drags the proton closer to the target nucleus than its own momentum would permit, were it not bound, it travels twice as high on the Coulomb barrier as the proton alone would climb. And the proton, being repelled and deaccelerated, slows the neutron until it is slow enough that it is more likely to fuse instead of "bouncing."

If the neutron gets close enough to the nucleus that the strong force takes over, that strong force, between the neutron and the target nucleus, will, again, through the strong force between the proton and neutron, pull the proton closer to the target nucleus until the Coulomb force repelling the proton is greater than the force binding the proton to the neutron, and at that point, the net force begins to accelerate the proton away from the nucleus; the "spring" of potential energy has reached its maximum "compression," and the proton now, being stripped from the neutron, and having half the mass that originally caused the "compression," recovers the energy of the deuteron, and, sometimes, then, some additional energy, which we can attribute to the strong force, as the neutron is stripped, pulling the proton closer, higher up the Coulomb barrier. This is the origin of the possible "negative energy" of the neutron, and why it is possible for the target nucleus, which, from fusion with a thermal neutron, would be left in an excited state, can even be left in the ground state.

I'm aware of many issues burbling around this. The description I've given uses the conceptions of classical physics, not those of quantum mechanics. I tried, in what I wrote in the article, to explain classically but to make the text compatible with the more modern -- and more esoteric -- understanding. I did not invent major explanations but used some analogies not present in the original, such as the compression of a spring, because I believe that these will make the article more accessible to the general reader. A related issue would be the use of cross section (physics) instead of "probability of interaction." Further, I think that cross-section could be a little misleading, because we aren't dealing with a single straightforward fusion process.

I.e., as I understand it from the paper referenced above, they were bombarding bismuth-209 with deuterons at energies where the expected deuteron fusion cross section with the target material is very low, yet they found nuclear effects that did not match the expected fusion products from deuterium fusion.

₈₃Bi + ₁D -> ₈₄Po + ₀n wasn't happening.

Instead, they saw radiation indicating:

₁D + energy -> ₁H + ₀n

together with

₈₃Bi + ₀n -> ₈₃Bi -> ₈₄Po + _-1e.

If I'm correct, the first reaction, with the emanation of neutrons, is what is obtained at energies that will overcome the Coulomb barrier. At the lower energies, the deuteron never fuses with the target nucleus. So what has happened is not an increase of the fusion cross-section. Indeed, at higher energies, sufficient that the deuteron isn't slowed to thermal velocities, the neutron capture can't take place.

I think it quite possible I've made many mistakes due to my recent unfamiliarity with the field. Please correct. --Abd (talk) 21:35, 22 June 2009 (UTC)

Sorry, that's just way too much text for me to make sense of. You'll have to condense your arguments into a few cogent points. I see that you have not changed the article at all, so I'm not sure with what statements you currently take issue. ScienceApologist (talk) 22:04, 22 June 2009 (UTC)

Okay, I'll make some edits, or bring some diffs here to discuss. But I'd hoped we could get clear on the science -- what is the OP process? -- before deciding how to best express it! --Abd (talk) 01:24, 23 June 2009 (UTC)

I see your first misconception here. The Coulomb barrier that is "violated" is the theoretical barrier associated with the Bohr model. The "actual" Coulomb barrier is different because of deuteron polarization. There is no violation of the Coulomb barrier, only the naive "first order approximation" that a nuclear physicist would start out with. ScienceApologist (talk) 01:33, 23 June 2009 (UTC)

I see nothing in our article about the Bohr model that relates to this article except one snippet: That the atom has a "small positively charged atomic nucleus," which, since the Bohr model is about the whole atomic structure, and especially about the electron structure, doesn't seem to me to be any kind of definitive statement about the structure or shape of the nucleus itself. If we assume that a nucleus is a single object with a uniform charge, sure, this model fails, but that isn't part of the Bohr theory; it seems to me that it treats the nucleus as a single small object because it is not concerned about structure on that scale, it's irrelevant to the orbits of the electrons. "Violation" of the Coulomb barrier isn't my language, where did you get it? I think we can just take out "expected from the Bohr model," so, please, revert this edit: .

But there is more. Neutrons aren't affected by the Coulomb barrier. The Coulomb barrier isn't overcome at all in the O-P process. This was the original language, my earlier version:

The process is considered important because it happens with high rate, with deuterons of sufficient energy, and because the required energy is much lower than expected from the Bohr model.

This was practically a direct statement from the source, where "commonly" was replaced with "high rate." In this context, I interpret "Bohr model" to refer to a simplified model of a nucleus, including the deuteron, as a simple body with no structure. In fact, for more complex nuclei, this is not a bad approximation, it fails with the deuteron.

You have, last version:

The process is considered important because it allows a nuclear interaction to take place at energies insufficient to directly penetrate the Coulomb barrier expected from the Bohr model, due to a polarization of the deuteron where the proton-end faces away from the incident nucleus and the neutron-end faces towards the incident nucleus during the most energetically favorable arrangement for the reaction.

I now think that the explanatory clause is too complex for the introduction. The mechanism will be explained in the mechanism section. Your language "insufficient to directly penetrate the Coulomb barrier" implies that it is penetrated indirectly. It isn't penetrated at all; in the strip reaction, the proton, the only part of the deuteron that is affected directly by the Coulomb barrier, never overcomes that barrier. Nor does the proton "help" the neutron to overcome it, for the neutron has no barrier to overcome. Paradoxically, the proton facilitates the neutron's fusion with the target nucleus by slowing it down, otherwise it would usually rebound.

I would simplify to this:

The process is considered important because it happens with a high rate, and because it allows a deuteron to cause a nuclear process without having sufficient energy to overcome the Coulomb barrier.

This follows the source. Coulomb barrier is explained in its article. We can explain how the deuteron manages to pull off this trick in the mechanism section. --Abd (talk) 02:34, 23 June 2009 (UTC)

You still have the misconception. First of all, the connection between cross-sections and reaction rate is imprecise in your formulation. The rate is some flux multiplied by the cross-section (see Nuclear cross section). Secondly, you are correct that what is being used in the Bohr model is a point-source nucleus. That's a good first-order approximation for most Coulomb barriers, but as soon as you add in extensivity to the nucleus you get second order corrections that change the Coulomb barrier to something else. It seems to me you think that there is something magical about this process that allows the deuteron fusion to contradict basic electrostatic repulsion which is simply not the case. All that is happening is that the neutron is able to get closer to the nucleus because of a polarization effect. The proton is kept further away from the target nucleus thus enabling a more efficient fusion process. ScienceApologist (talk) 02:53, 23 June 2009 (UTC)

You still have the misconception. There are these possibilities:

1. I have a misconception. Assuming I'm not stupid, this would mean that I haven't understood the explanations. The probable cause of that is that it hasn't been well enough explained, which points to a probable deficiency in the article, since my background is deeper than that of the average reader. My goal here is clear text, and my own understanding I take as a measurement of that, and we should verify that with the understanding of more normal readers. Not you or I.
2. I don't have a misconception, but you do. In which case, our text -- and sources cited -- have been inadequate to explain the matter to you. The solution is the same as with the first possibility: continued work on the text.
3. Neither one of us has a misconception, but we have not developed the rapport to be able to understand each other, one way or the other or both. From the above, I know that this is happening to some degree. The solution is patience and an understanding of the importance of a cooperative attitude.
4. Both of us have failed to understand this process. Solution: we will ultimately ask an expert to review. I'm not an expert, I'm merely more informed than normal. If you are an expert, SA, then this is my general position on true experts: they shouldn't edit articles within their expertise except non-contentiously. Experts should advise in Talk; experts frequently have a strong POV and often have some level of contempt for those with lesser knowledge. Misplaced Pages needs to develop better guidelines and procedures for dealing with experts, they often end up banned, and probably needlessly.

My text simply says that the process happens with a high rate. That's deliberately imprecise, though it's true and the implications are true. Certainly, rate, in this usage, is a product of cross-section and flux. The original source was even more imprecise, "because it occurs very commonly," which could be read as, this is something that happens frequently, in general, when it doesn't. What's true is that if we set up deuteron bombardment of a target, with the deuterons being of sufficient energy to approach the nucleus to within "striking distance," but well below the energy where ordinary fusion cross-section is appreciable, we see O-P isotopic transmutation (apparently it's easier with nuclei of higher atomic number and eventually all this should be explained in the article, assuming there are sources, which I believe there are.) The link with "high rate" should indeed be Nuclear cross section, that's more specific, and it seems you are referring to "total nuclear cross-section," or possibly to the cross section for the specific reaction of neutron absorption.

Your text says The process is considered important because it allows a nuclear interaction to take place at energies insufficient to directly penetrate the Coulomb barrier expected from the Bohr model.... This really says little more to our reader than "high rate." "directly" implies that the barrier is indirectly penetrated, when it isn't penetrated at all.

If the goal is neutron fusion, we could accomplish it in a number of ways. One would be to bombard with neutrons. For starters, generating high neutron flux is difficult, not to mention dangerous, etc. It's hard to focus a beam of neutrons, they don't respond to electrical or magnetic manipulation. Then, if we have a beam of neutrons, they have too much energy, they won't generally fuse, most of the collisions will simply scatter the neutrons. So we could use a moderator to slow the neutrons. With the O-P process, the positive charge on the proton allows the deuteron to function as a carrier that slows the combination when it encounters the Coulomb barrier, and then, once the deuteron is sufficiently slowed, the neutron is "handed over" to the nucleus at low or even negative energy.

Apparently I correctly inferred the reason why the "Bohr model" is inadequate. That wasn't present in our article, neither this one nor Bohr model, and using the terminology doesn't inform a reader, it simply complicates the explanation, and over-complicated initial explanation is a common error in technical writing. It's necessary to begin with simple, overall concepts, then guide the reader through more detailed explanations.

It seems to me you think that there is something magical about this process that allows the deuteron fusion to contradict basic electrostatic repulsion which is simply not the case. No. You obviously have not considered the article text I wrote, nor my explanations here. I described exactly how electrostatic repulsion operates, using a classical model and considering the deuteron as "like a barbell." The O-P process, to repeat, does not "overcome" or "violate" the Coulomb barrier. I will not speculate on why you haven't understood me, but I'll note that it's not obscure, given other history. I suggest this discussion as an opportunity to overcome old problems, and I'm quite sure that our discussion will improve the article, and rapidly. --Abd (talk) 13:28, 23 June 2009 (UTC)

Here's the issue: I think precision is extremely important. What is occurring in the O-P process is an increase in the effective cross-section of the target nucleus due to the deuteron's charge polarization. This is the most precise way to say it, and is how someone would describe it if they were going to make an empirical model. Theoretically what is happening is a spatial separation of charge which allows for the energetically unfavorable arrangement (like charges adjacent) to be mitigated by an increase in the distance between the target and the deuteron. What we may wish to do is totally rewrite the explanation to make sure that we are unassailably precise. We do not want the reader to come away from this article thinking that there is something going on that allows for the deuteron to violate the energetics of a Coulomb barrier. Nor do we want them to come away from the article thinking that this is a process which occurs all the time (it still requires a substantial amount of energy, just less than an arrangement where there is no charge polarization). I think those should be our goals for the prose. I'll try to word something to that effect. ScienceApologist (talk) 15:03, 23 June 2009 (UTC)

There may be a general issue about encyclopedia content here. Sure, precision is important, but there are general statements and specific statements. Ideally, they don't contradict one another. A precise statement, however, with all the necessary qualifications, can be so complex that a general reader won't understand it, and it may be better to make a general statement that is consistent with a precise understanding, but which does not specify every detail, the detail being supplied as the reader proceeds, step by step, through the explanation. I do agree on most of what is written above on the process. There is insufficient precision, however, ironically, in the statement about the "increase in effective cross section." Which cross section? There are three involved: the cross section for neutron capture, the cross section for deuterium fusion (which requires overcoming the Coulomb barrier, at least in this situation!), or the overall "any nuclear reaction" cross-section. Further, the term "cross section" doesn't directly convey the needed meaning to the reader. Does the reader need to read that article before moving on? What's wrong with "rate," or ordinary language? I settled with rate, or language like that, with a wikilink to cross-section. That makes reading the detailed article clear, but not necessary for basic comprehension. It's also possible to have rate (nuclear cross section), or the reverse, i.e., the technical term first and the explanation in ordinary language second, but my sense is that it's really not necessary. Are we trying to explain the O-P process, or educate the reader in all the technical language they might encounter elsewhere. They don't need to know what "cross section" means to a physicist, at all, in order to understand the O-P process. Hence my view that this adds complexity without being likely to increase comprehension or make comprehension more accurate, and we should avoid that. Experts, particularly, can be vulnerable to doing this. That's why they need editors! What we want, in the end, is to have text that is clear, readily comprehensible without likely error, and signed off by an expert as accurate. It takes work, usually. Now, very specific:

What is occurring in the O-P process is an increase in the effective cross-section of the target nucleus due to the deuteron's charge polarization. If "cross-section" means "likelihood of any particular flux of particles to cause any nuclear reaction," Yes, that's what is happening, but this is a description of the outcome of the process, not the mechanism, and it's expressed in a manner that someone in the field will readily recognize, and that someone without the scientific background will walk away puzzled by the jargon. I urge you to express this in ordinary language, without technical terms that aren't necessary. "Deuteron" at this point is necessary, for example. "Cross section" isn't, and, because of the unclarity of what kind of cross section is involved, merely confuses. When we go into an explanation of how the effect works, the reader will not encounter "cross section." Later, if we go into actual details of the reaction rates, the term would probably be introduced.

Theoretically what is happening is a spatial separation of charge which allows for the energetically unfavorable arrangement (like charges adjacent) to be mitigated by an increase in the distance between the target and the deuteron. What's happening is that the deuteron is (under these conditions) like a barbell, and if one end of the barbell is prevented from getting close enough to fuse, that doesn't prevent the other end, not itself repelled, from swinging around and approaching the nucleus. If we really want to explain this well, we'd give actual distances, and we'd note that the deuteron is practically unique in having such a wide separation between its two constituent nucleons (in effect), such that its polarization is important. I'm telling you, SA, that your explanation of the process may be precise -- though I find the second half of this statement unintelligible, did you get it backwards? -- but it isn't effective explanation for an ordinary reader.

We do not want the reader to come away from this article thinking that there is something going on that allows for the deuteron to violate the energetics of a Coulomb barrier. That's right. Absolutely, we don't want that.

Nor do we want them to come away from the article thinking that this is a process which occurs all the time (it still requires a substantial amount of energy, just less than an arrangement where there is no charge polarization). This actually is imprecise. The reason is that "it" is undefined. If "it" refers to neutron capture, "it" doesn't require much energy at all, and, in fact, the obstacle is often that the neutrons have too much energy. My sense is that with the reactions where the O-P process works, thermal neutrons would do the same job, just fine. (For others, that means "very low energy neutrons.") If "it" means deuterium fusion, "it" doesn't happen at all with the O-P process. If, however, we are referring to a deuteron beam, of modest energy (sometimes even less than the binding energy of the deuteron, and, to be complete, we should describe the energies involved specifically), causing a target to become radioactive, "it" happens at high rate. Under the obvious condition that you've got these energetic deuterons!

That text also implies some continuity with standard fusion (i.e., of the deuteron, which happens at higher energies). This isn't standard deuterium fusion, and it isn't continuous with it, i.e., simply an increase in the reaction rate or cross section.

Paradoxically, the O-P process uses the Coulomb barrier to facilitate neutron fusion. That barrier is essential to it, it slows the deuteron to the point where the neutron is slow enough to react with the nucleus.

Personally, I don't mind, SA, if you write article text per your own original research or personal understanding, without having to extract every fact from sources. One of the ways we get badly written articles is exactly that. Once the article explains the topic well, sources will ordinarily follow, I don't think we are blazing new ground here! To me, the point is to find real consensus on the substance, and then set up verification for full compliance with guidelines. Writing good articles is a process; it should ideally start with a clear understanding of a topic, proceed through clear expression of that for the general reader, and be cleaned up and sourced as part of the editorial process. Writers who can produce, ab initio, fully-sourced, perfect text, are quite rare, and I'm not at all convinced that they are better writers for it, and that's why publishers employ editors and fact-checkers, etc. --Abd (talk) 16:36, 23 June 2009 (UTC)

Pretty good. Now, for a possibly more contentious issue:

Pretty good, ScienceApologist. Some details have been lost. For example, the heavier product nucleus may even be left in the ground state, which wouldn't occur with ordinary neutron capture (with thermal neutrons).

Now, possibly a more contentious issue:

The Coulomb barrier sets the requisite energy that interacting atomic nuclei need to fuse. The coulomb barrier does not set that energy, except under certain conditions. That's why I qualified this statement with "ordinarily." It's not absolute, for at least two reasons: first, tunneling, which means that some level of fusion takes place below the energy implied by the Coulomb barrier, and second, catalysis, where some effect screens the repulsion, the most accepted form being muon-catalyzed fusion. There may be others, such as proposed to explain Cold fusion, in the Tetrahedral Symmetric Condensate theory of Takahashi (for which there is secondary RS), or the Bose–Einstein condensate theory published this month in Naturwissenschaften, or the wild hydrino theory where electrons with reduced energy, below ordinary "ground state," might serve in a manner similar to muons. My point isn't to bring up the whole cold fusion controversy here, but simply to note that there are at least two and possibly more than two exceptions to what was written as an absolute. --Abd (talk) 17:05, 23 June 2009 (UTC)

• Stub-Class physics articles
• Unknown-importance physics articles
• Stub-Class physics articles of Unknown-importance