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note: because important websites are frequently "here today but gone tomorrow", the following was archived from http://matpitka.blogspot.com/2010/11/why-positrons-are-so-shy.html on 11/08/2010. This is NOT an attempt to divert readers from the aforementioned website. Indeed, the reader should only read this back-up copy if the updated original cannot be found at the original author's site.
Why Positrons are so shy
Matti Pitkänen / November 5, 2010
Postal address:
Köydenpunojankatu 2 D 11
10940, Hanko, Finland
E-mail:
URL-address: http://tgdtheory.com
(former address: http://www.helsinki.fi/~matpitka )
"Blog" forum: http://matpitka.blogspot.com/
http://www.newscientist.com/article/dn19682-cloaking-effect-in-atoms-baffles-scientists.html
"Cloaking Effect" in atoms baffles scientists
by Hazel Muir / New Scientist Nov. 4, 2010
Atoms called Positronium inexplicably scatter off gas particles as if they were lone electrons even though they contain an anti-electron as well. The finding hints that engineers could use the well-known scattering properties of electrons as a rule of thumb in designing future medical scanners that employ Positronium. It could also help interpret puzzling astronomical observations.
"Knowledge of how Positronium interacts with the surrounding medium is important whether this is human tissue or interstellar gas," says experiment leader Gaetana Laricchia of University College London.
Positronium atoms are like Hydrogen atoms except that the proton is replaced by a positron ( the positively-charged antiparticle of the electron). The atoms are unstable and their 2 constituent particles disappear in a puff of gamma rays within a microsecond.
When a beam of electrons or positrons flies through a gas, they scatter off the gas particles at predictable rates. Scientists guessed that Positronium atoms -- being twice as heavy as an electron and electrically neutral -- would have very different scattering rates.
Competing effects
To test this, Laricchia's team fired Positronium atoms at 1,100-to-4,400 kilometres per second into various gases including Hydrogen, Krypton, and water vapor. Curiously, the scattering rates for positronium were almost identical to that of a plain electron as though the positron's influence was somehow "cloaked".
James Walters, a theorist at Queen's University Belfast who studies matter-antimatter interactions, says the result will be tough to explain mathematically because the scattering process is so complex.
"When Positronium hits an atom, the electrons in the atom don't know what to do. Do they stick with the nucleus or try to chase after the positron?" he asks. "There's a lot of competition going on and theoretically it's difficult to model that accurately."
Limiting damage
Laricchia speculates that the electron might play a dominant role in each Positronium scattering by getting closer to a gas particle -- on average -- than the positron does.
Whatever the reason for the strange results, they could have important consequences for medical PET (positron emission tomography) scanning. PET scanners pick up gamma rays emitted by Positronium formed when a radioactive tracer that emits positrons is injected into the body.
Knowing the Positronium scattering rates should clarify how the particles deposit energy along their tracks as they collide with molecules in tissue. "That's required to limit damage to healthy tissue," Laricchia told New Scientist. It would also help refine estimates of how far Positronium travels, allowing tumor volumes to be measured more accurately.
Positronium also forms in space. Understanding its interaction with interstellar gas clouds could prove crucial for determining the positions of some mysterious positron sources in the Milky Way (right).
Comments
1. Is This Really That Baffling"
by Mulder / Fri Nov 05, 2010 19:06:40 GMT
Obviously when the scattering process occurs it is mediated by the electron. The positron plows into the electron clouds of the atoms ***as a separate entity*** - annihilates emitting a gamma ray which may down-convert or pair-create.
From the reference frame of the Positronium, the oncoming gas molecules have a short wavelength and are able to probe the Positronium as 2 particles (not a composite indistiguishable particle). One process is a relatively low-energy scattering event (hence the conventional result). The other is a high energy annihilation-creation event.
2. re. Is This Really That Baffling
by Mark Bridger / Sat Nov 06, 2010 07:21:08 GMT
Mulder, you could be right. But then why are scientists baffled by this result?
Maybe there is another hint here that we don't yet have a full understanding of the nature of the atom. The other hints being a smaller proton in the muon atom (see here). And the large proton halo calculation (see here).
I believe a fuller understanding of the atom will also help to explain dark matter(s); the apparent "alpha axis"; how matter was generated at the birth of the Cosmos; and why there happens to be more matter than anti-matter. And with that newer, more complete understanding, we should be in a better position of knowledge to achieve efficient nuclear fusion.
Re Positronium: in my understanding, its instability is due to it not really being an atom (which should have a nuclear particle in it). The electron might -- given the Uncertainty Principle -- appear briefly, virtually, atomically-bound but must soon become a separate particle. Especially in the real moment of or by the time of scattering.
Why Positrons are so shy
Matti Pitkänen / November 5, 2010
Postal address:
Köydenpunojankatu 2 D 11
10940, Hanko, Finland
E-mail:
URL-address: http://tgdtheory.com
(former address: http://www.helsinki.fi/~matpitka )
"Blog" forum: http://matpitka.blogspot.com/
There is really dramatic news in New Scientist (see above). Positrium atoms consisting of positron and electron scatter particles almost as if they were lonely electrons! This is called the "cloaking effect" for positron. If this is not a bad joke, this is something totally devastating from the point-of-view of QED and all that we have believed until this day;-).
I have said the words "many-sheeted space-time" and "dark matter hierarchy" so many times that it should be easy to guess that the following arguments will be attempts to understand the cloaking of positron in terms of these notions.
1. Let us start with the erratic argument since it comes first to mind. If the positron and electron correspond to different space-time sheets and if the scattered particles are at the space-time sheet of electron, then they do not see positron's Coulombic field at all.
The objection is obvious. If a positron interacts with an electron with its full electromagnetic charge to form a bound state, the corresponding electric flux at the electron's space-time sheet is expected to combine with the electric flux of electron so that Positronium would look like neutral particle after all.
Does the electric flux of positron return back to the space-time sheet of Positronium at some distance larger than the radius of atom? Why should it do this? No obvious answer.
2. Assume that Positron is "dark" but still interacts classically with the electron via Coulomb potential. In the TGD Universe, "darkness" means that positron has large hbar and Compton size much larger than Positronic wormhole throat (actually wormhole contact, but this is a minor complication) would have more-or-less constant wave function in the volume of this larger space-time sheet characterized by zoomed up Compton length of electron.
The scattering particle would see a point-like electron plus background charge diffused in a much larger volume. If hbar is large enough, the effect of this constant charge density to the scattering is small and only an electron would be seen.
3. As a matter of fact, I have proposed this kind of mechanism to explain how the Coulomb wall (which is the basic argument against cold fusion) could be overcome by the incoming deuteron nucleus. Part of deuterons in a Palladium target would be dark and have a large size just as the positron in the above example.
Also, one of my proposals for the absence of anti-matter is that anti-particles reside at different space-time sheets as dark matter and are apparently absent. Cloaking positrons (shy as their discoverer Dirac;-)) might provide an experimental proof of this idea.
Comments
1. At 11:34 AM, Ulla said...
This would act as a Dirac cone. It is hard to explain in any other way.
The doomsday of M-theory? And they will fall deep. I missed this one, but yesterday was a great TGD-day. Also the changing Planck constant maybe can be proved. In fact, it has been proved already since 1986, I found out. From CERN. :) http://physics.aps.org/articles/v3/8
Alpha clustering in light nuclei is now well established. These states are found at the decay thresholds in nuclei with neutron number equal to the atomic number (N=Z) and having total mass A<30. In many instances, they are associated with chains of α particles forming elongated, exotic shapes.
For instance, the so-called Hoyle state in C12 -- whose existence is essential for the nucleosynthesis of Carbon via the triple-α process -- is an example of an α-cluster state. Because these configurations cannot be described by the shell model, so-called cluster models have been developed to characterize these states. In heavier nuclei, cluster states have not been observed. Nevertheless, the concept of α particles existing inside the nucleus even in heavier systems is employed in order to describe α decay.
A cluster of He-atoms? Gravity forms the strings (on shell) as a condensate? Is this the proof for a changing hbar too?
Thanks Matti for being there. Let's kick the boy in the ass now :) Out into the world with him!
2. At 12:37 AM, Matti Pitkanen said...
… I have been working with Quantum Biology and the Quantum Theory of Consciousness since 1995-or-so. For a decade, I spent more time with these topics than TGD proper since the situation in theoretical particle physics had become very frustrating (for reasons that we all know). After 2005, the focus has been more in the mathematical and interpretational aspects of TGD proper since many new ideas emerged.
Maybe this decade will be a new Golden Age of Theoretical Physics when all certainties will be challenged. For instance, the finding about Positronium may force us to profoundly modify the views about matter-antimatter asymmetry and CP breaking, which after all belong to basic mysteries of recent day Physics. I believe that this kind of experiment could have been done for decades ago. If it were, what would Physics look like now? Interesting question.
3. At 1:06 AM, Ulla said...
It is exactly the biology and the consciousness that is the main proof for TGD :)
How can a theory of Physics ever neglect Biology as if living things never exist? That is the most stupid thing they could ever have done. It is exactly Biology that leads to the right theory of Physics. … …
4. At 3:14 AM, Ulla said...
The many faces of QCD, Valentine Zakharov about scalar fields. https://docs.google.com/fileview?id=0B97SuPi0LQhqZTg0ZTkxYzgtZDEwYy00NzZiLWJjZmItMDQ4ZjkwZWJhNTY1&hl=en&pli=1 . Field theory seems to fail; dual geometry will do it. Go to the lattice.
Quasi-solution because of the need for fine-tuning. Singular monopole solutions, infinite clusters emerge. Surfaces as defects. Dual gluon fields. It is much about areas.
Condensed strings are to be magnetic , zero magnetism, and topology-charged, time-oriented, Higgs mechanism with Goldstone bosons. Has he studied TGD? :)
Entanglement entropy is alpha entropy. That was new to me. How does the entropy succeed with 2 different alphas of Graham D.?
There is an entropy problem with BB. 2 different entropies?
5. At 3:53 AM, LEO VUYK said...
In my humble view, elementary particles are hardrock strings pushed around by the oscillating Higgs vacuum lattice.
If the electron and positron string "click together into a neutral Positronium, then the cross-section of this entity is about the same as one electron. As a result, the scattering effects on argon are not very much changed.
http://3.bp.blogspot.com/_ArDoWzECXSo/RpOCJjlPsTI/AAAAAAAAALg/Vv6ljD45e7M/s1600-h/positronium+ortho-para.jpg
http://bigbang-entanglement.blogspot.com/2007/01/introduction.html
6. At 4:20 AM, Matti Pitkanen said...
To Leo Vuyk,
I think that the basic challenge is to explain the characteristic angle dependence of the scattering on a charged particle.
I am not sure whether a scattering from a purely geometric object with vanishing charge -- or in improved approach from electric dipole -- can reproduce this (as a matter of fact, the Coulomb scattering cross-section diverges) and scattering amplitude also in forward direction.
Constant background charge density gives a rather minor correction to the scattering amplitude which is non-vanishing only in forward direction when the size of positron becomes very large.
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