Proton Magnetic Fields

1. Dec 30, 2004

FulhamFan3

We all know that magnetic fields come from moving charge or electron spin.

However if it were possible to have protons as a moving charge in a wire does that cause a B field?

At first I thought that it obviously should but then I thought about how accelerating electrons emit EM waves. That would mean protons can also emit and absorb photons which I think is weird.

Is this possible or are EM waves unique to electrons?

2. Dec 30, 2004

Integral

Staff Emeritus
ANY accelerating charge is a source of EM radiation. Electron, proton or ion, it does not matter. In chemical solutions ions are usually the majority current carriers rather then electrons. Any mobile charged particle can be a current carrier and therefore be the source of EM radiation.

I do not know of any way that you will have mobile protons in a 'wire'. In every thing that I know of which is used for a wire protons are locked in the crystal lattius, therefore are not mobile so cannot be the current carrier. However, as I said above, ions. which may either postitive or negitive, can be current carriers.

Last edited: Dec 30, 2004
3. Dec 30, 2004

ZapperZ

Staff Emeritus
As Integral has explained, the GENERAL rule is that EM radiation is generated via ANY accelerating charge. If a glob of stuff has a charge, and it is being accelerated, you will have EM radiation. Period.

We have many particle accelerators using protons (example: Tevatron at Fermilab), large charged nuclei (RHIC at Brookhaven). These people can easily tell you that these things certainly generate a LOT of radiation when they are accelerated (just look at the amount of shielding required around the storage ring alone).

And while we do not have a proton current flow normally in solids, we can have positive charge flow via the positively charged holes in p-type semiconductors. We know that it is a positvely-charged majority charge carrier via the Hall effect.

Zz.

4. Dec 30, 2004

FulhamFan3

Thanks guys. Although Zapper brings up another question. Even though positive CHARGE moves in a semiconductor no positive PARTICLES. Is that enough to create a B field?

Integral. I know there isn't a situation where mobile protons move in a wire. It's a theorectical construct like einsteins light clock. It's not something we'll ever see but you can still get good physics from it. Anyway I think a proton-beam would be the samething.

5. Dec 30, 2004

krab

Zz: the shielding around most hadron accelerators is unrelated to the radiation emitted by the accelerated particles. It is due to the energy being sufficient to radioactivate the environment.

Ff3: Protons in a wire is not so theoretical-only. As Zz says, proton currents flow in proton accelerators. It's just that the "wire" is actually a vacuum chamber. You can measure the magnetic field created, and also, accelerated protons emit photons. You may have gotten the misconception that only electrons emit because of the fact that the emitted power is very mass-dependent:
$$P\propto 1/m^4$$
Thus, an electron of given energy passing through a magnetic field (that accelerates it sideways) emits 1800^4= 11 billion times as much energy in photons as a proton would.

6. Dec 30, 2004

Gokul43201

Staff Emeritus
I'm not sure if you mean the same thing, but what I thought was that some of the ions will unavoidably strike walls of the vacuum chamber, or the collimators and such, producing gamma rays (and possibly neutrons as well). The purpose of the shielding, was to block this radiation.

I thought this was the dominant source of radiation, and it seems that krab is suggesting something similar.

7. Dec 30, 2004

krab

Yes. What I mean is that the particles are energetic enough that when stray ones hit the vacuum chamber walls, or air molecules or whatever, they can penetrate right into other nuclei and break them up. The resulting debris contain unstable nuclei that emit alpha, beta and gamma radiation.

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