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Name: Juniper
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Question:
can an electron emit an endless supply of photons? in particle accelerators the electrons race around and around and photons are released and studied. I wonder if the same electrons can continue to emit photons or if they dry up?



Replies:
Sure they can emit photons without being used up.
- no electron emits any photon if it is alone and undisturbed. It does not seem to have any internal structure with which to do such a, uh, distinct self-initiated action.
- what emits in a cyclotron is not just the electron, but rather the combination of a moving electron and a magnetic field pushing it sideways pretty hard. This combination does not consume the electron. It just converts some of the kinetic energy the electron has, to the electromagnetic energy in the emitted photons.
- emitting the photon in the magnet-induced turn will slow the electron and maybe deflect it sideways. Will the cyclotron lose its control of the deflected electron, or catch it and re-circulate it? For visible light photons ~ 2eV, and fast electrons >1MeV, the change in trajectory is pretty small, so I think most cyclotrons will successfully snag a large majority of the electrons after they emit their photon of "cyclotron radiation". But I do not really know. Partly it depends on the equipment in the cyclotron. Partly it depends on the sharpness of the turn. A stronger field makes a sharper turn which makes higher-eV photons. (I wonder if one electron emits multiple photons to go around a long curve?)
- there may be some small loss rate, so there will need to be some small make-up rate of added electrons. This is true in any case, because the vacuum in the machine is not usually perfect.

Jim Swenson


Juniper,

Electrons emit photons because they first get energy inputted into them (excitation) and then the release that energy (relaxation). Through this process the electron losses or gains no net energy, so as long as there is a source to continually excite the electrons, they will continually relax and emit photons. The electron remains the same before and after this process.

Matt Voss



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