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Buckeye
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When electrons collide with positrons, we get gamma-rays and other particles. Keeping in mind E=mc^2, is the result better called "annihilation" or "conversion"?
malawi_glenn said:The process when a particle meets its antiparticle is called annihilation.
An example of "conversion" is "Internal conversion" , when an exited nucleus interacts with the atomic electrons which takes a way the excitation energy - instead of the nucleus emitting that energy in form of photons (gamma radiation)
Buckeye said:OK. Does the word "annihilation" mean the total destruction of the particles?
malawi_glenn said:
Buckeye said:Wikipedia is not necessarily a reliable source, but let me ask this. If annihilation means the total destruction of particles, then why do we get two photons? The production of something from the interaction of something else seems like a conversion. Why is this process called "annihilation"?
malawi_glenn said:I know that article is a good one.
Energy can't be destroyed, only converted. So you can call it a conversion process of energy.
It is called annihilation since it refers to the particles in the initial state, they are the ones beeing totally destroyed. And the emphasis is on the particles perspective since we are dealing with particle physics.
This is consistent (the definition of annihilation vs. conversion) with the internal conversion process, where energy is converted to kinetic energy of an atomic electron instead of photon radiation (roughly speaking).
Fundamental, you gain only one photon in the electron-positron vertex, but that photon will be virtual! So in order to get a real photon, either the electron or the positron must radiate of a photon before annihilation (1st order feynman for real annihilation). http://www.shef.ac.uk/physics/people/cbooth/eegg.gif [Broken]
In this way, you combine two virtual diagrams, to constitute a real-non virtual-diagram.
And this is also in agreement of experiment, QED is the best tested physical theory there is. It is amazing i must say :-)
So a summary: Annihilation of particles, conversion of energy
Buckeye said:OK.
What is the meaning of the equal sign (=) in the equation E=mc^2?
Does the equal sign indicate annihilation or conversion?
malawi_glenn said:The "=" sign refers to that mass is a form of energy, just as there is kinetic energy, potential energy etc.
So the equal sign plays a role both in annihilation and conversion, annihilation is 'followed' by conversion. The initial energy of the positron and electron (both mass-energy and kinetic energy) is converted to photon(s) with the same energy.
The answer to the question "Does the equal sign indicate annihilation or conversion" is (again) that the question itself is wrong. The equal sign just tells you how much energy you can get from a mass [tex] m [/tex]. Just as [tex] E_{kin} = mv^2/2 [/tex], etc. In fact, the full formula for energy of a (free) particle (i.e no potential) is [tex] E^2 = (mc^2)^2 + (pc)^2 [/tex].
malawi_glenn said:I would not bother, as long as one knows what all is about and what is happening.
I would still stick that the energy is converted, from the form of real particles (electron,positron) into the form of photons (another kind of particle). The term annihilation refers to that the particles in the initial state stops to exist.
the term 'made' is a quaite amateurish word, i would write "the particles are not actually converted into nothing, but rather into new particles - c.f electron-positron colliders"
malawi_glenn said:The "=" sign refers to that mass is a form of energy, just as there is kinetic energy, potential energy etc.
So the equal sign plays a role both in annihilation and conversion, annihilation is 'followed' by conversion. The initial energy of the positron and electron (both mass-energy and kinetic energy) is converted to photon(s) with the same energy.
The answer to the question "Does the equal sign indicate annihilation or conversion" is (again) that the question itself is wrong. The equal sign just tells you how much energy you can get from a mass [tex] m [/tex]. Just as [tex] E_{kin} = mv^2/2 [/tex], etc. In fact, the full formula for energy of a (free) particle (i.e no potential) is [tex] E^2 = (mc^2)^2 + (pc)^2 [/tex].
Buckeye said:Unfortunately, not all textbooks are well written so many students will get the wrong idea. Government leaders who control funding are relying on Wikipedia for information and definitions when they justify the release of money to colliders, universities and the like.
malawi_glenn said:i) I agree that many textbooks and resources are quite unpedagocail.
iii) How to define a particle depends on what representation you use to describe a physical system. An elementary particle, I would say that it is an entity with no internal structure. It is not made up of anything else than it self and can not be divided into smaller pieces nor have excited modes nor undergo decay.
iv) What do you mean by "only measures momentum"? One wants to detect energy and ionization loss also, otherwise we don't know what particle we detected. Measuring only momentum is trivial, just have a track chamber and a magnetic field close to the interaction vertex. Measuring only momentum is useless.
v) The most probable annihilation mode of electron and positron is if they annihilate in (almost) rest, then the two photons will have an energy of 0.511MeV each, and emitted in right angles of each other.
vi) You can create higher energy photons from annihilation aswell, and also more than two photons from electron-positron annihilation aswell.
vi) The probablity for [itex] p [/itex] [itex] p \leq 2[/tex] photon emission in one annihilation process are related to those of 2 photon emission as:
[tex] \frac{\text{Rate}(e^+e^- \rightarrow p\gamma )}{\text{Rate}(e^+e^- \rightarrow \gamma \gamma )} = \mathcal{O}((p-2)\alpha) [/tex]
Independent of energy, i.e 4 photon emission is (1/137)*(1/137) times the probability to get 2 photon emission.
I thought you had 80 books about quantum physics, that you had read from cover to cover?
malawi_glenn said:iii) Separate and distinctive existence (reads in my philosophy book)
v) Energy and momentum conservation, here is a whole thread devoted to that process, where I try to teach a guy from eastern europe how it works. https://www.physicsforums.com/showthread.php?t=226986
vi) how about google: positronium - orthopositronium (which is 3 photon decay) ? which have been know for very long.
My class mates from Germany said that they might have seen 4 photon decay in positronium, can talk with them again when I see them on tuesday.
malawi_glenn said:besides, there is no collision axis if the electron and positron annihilates at rest.
Also, do you have reference on your statement "photons come out at 90 deg angles to the collision axis"
malawi_glenn said:"no one has a detector that only measures Momentum"
Can you elaborate? You are just goofing.
Have you studied orthopositronium yet?
We haven't been able to detect dark matter yet since it does not interact under any of the forces other than gravity.Buckeye said:Nope, not goofing. Thinking. Why can't we detect dark matter?
Ok, could you please tell us what a "momentum only" detector is? Note that you are only permitted to talk about mainstream, or published, peer-reviewed material here. If what you are suggesting has not been peer reviewed, then the only place in which you can discuss it is the Independent Research forum.Buckeye said:Maybe because it has no EM properties which means a momentum only detector might be able to detect dark matter.
Annihilation or conversion refers to the process in which matter is transformed into energy, or vice versa. This concept is based on Einstein's famous equation E=mc^2, which states that mass and energy are interchangeable.
Annihilation or conversion can occur through several different processes, including particle-antiparticle annihilation, matter-antimatter reactions, and nuclear fusion or fission reactions. These processes involve the transformation of particles or nuclei into energy.
Annihilation or conversion has significant implications in the fields of physics and astronomy. It helps us understand the fundamental nature of matter and energy and plays a crucial role in our understanding of the universe and its origins.
In everyday life, annihilation or conversion is not a dangerous process as it only occurs in extreme conditions, such as in nuclear reactions or in the center of stars. However, in certain scenarios, such as in nuclear weapons or accidents at nuclear power plants, it can have catastrophic consequences.
In theory, annihilation or conversion can be reversed through the process of pair production, in which energy is transformed back into matter. However, this process requires immense amounts of energy and is not currently feasible with our current technology.