# Understanding what happens when particles have a higher energy

abotiz
Hi,

Iam having trouble understanding (or actually picturing) things I have learned, now that I look back at it.

When the photon have a higher energy, what does this mean besides the frequency is higher? Does the photon "cover" a smaller area because it turns up and down so quick so it does not have much time to go "far up and far down"?

Also, about the Neutron - Boron inteaction (the capture). When the Neutron has a high energy the cross section is low, but when the neutron has low energy the cross section is high. Is there an intuitive answer to this?

Basically, what happens or what is the difference when the particle have a higher energy
1) Photons
2) Charged particle (protons and electrons), e.g. does the electric field around them expand
3) Neutral particles (neutrons)

Regarding #2, I do know that when you accelerate a charged particle to light speed, it will never reach light speed, instead its mass would expand instead (E=mc^2). But what else happens, the classical-physics would say it would have a higher speed, e.g. will be in point A in less time. But the relativistic answers are interesting!

Also, the electron is not a particle right? Its like a cloud? This makes it more interesting to what happens when it is accelerated.

Thank you!

RGevo
Hi Abotiz,

I can try to answer some of these.

Basically, what happens or what is the difference when the particle have a higher energy
1) Photons
2) Charged particle (protons and electrons), e.g. does the electric field around them expand
3) Neutral particles (neutrons)

So for the photon, we can measure the energy of the photon by looking at its frequency or wavelength.

E = hc/lambda

Meaning for a very high energy photon...it has a small wavelength. If we want to understand this qualitatively, we can think of the photon as being a probe/measuring device. If you have a metre stick with only 1cm divisions, it is hard to say anything about the size of objects smaller than 1cm. All you can really say is that it is smaller than the 1cm division. The same is true for the photon. It cannot resolve objects smaller than its wavelength. Therefore, if you want to look at very small things you need to get very high energy photons.

The electron is a 'point-like' particle. Meaning, it may not be a point in reality... just we haven't found a high enough energy probe to resolve the object. It terms of cloudiness, I think you are referring to 'self interactions'. The electron is charged, so you can imagine it interacting with pairs of charged particles (via photons) in its presence.

In fact this is seen by measuring the electromagnetic coupling 'constant' at different energies. At high energies, the coupling gets stronger as you probe more deeply into this 'cloud' and are less effected by shielding from these other interactions around the electron.

Under acceleration particle radiate, if they are electromangetically charged this could be photons. If they are colour charged (like quarks) this could be gluons (as well as any other interactions possible for the particle in question).

I'll leave the neutron for someone else to comment!

Hope this helps

Mentor
Also, the electron is not a particle right? Its like a cloud? This makes it more interesting to what happens when it is accelerated.

The electron most certainly is a particle.
What's throwing you here is the way that (for historical reasons) we use the word "particle" to describe the various subatomic things even though they do not behave like little grains of sand, except smaller.

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Mentor
Also, about the Neutron - Boron interaction (the capture). When the Neutron has a high energy the cross section is low, but when the neutron has low energy the cross section is high. Is there an intuitive answer to this?

Intuitively the neutron capture cross section is higher for the low energy neutron for the same reasons that a slow-moving fly is more likely to stick in a spider's web than a fast-moving one.

WARNING: This sort of "intuitive" hand-waving is no substitute for learning the underlying physics. You cannot reliably generalize it to other similar-looking problems, and if taking it at face value causes you confusion, the problem is in the hand-waving, not the physics.

Mentor
Regarding #2, I do know that when you accelerate a charged particle to light speed, it will never reach light speed, instead its mass would expand instead (E=mc^2).

That's not quite how it works (consider, for example, that right now you are moving at 99.999% of the speed of light relative to someone somewhere in the universe, but nothing strange is happening to your mass). There are some good threads over in the relativity forum on this. For now, I'll just mention that the various interesting relativistic effects apply equally to charged and uncharged particles.