1. Sep 11, 2009

CT03

i am not sure if anyone have asked this question, but can someone explain to me how synchrotron radiation have a wide range of spectrum? I thought that an electron only emit a photon with a spectific range of energy depending on the energy loss.

2. Sep 11, 2009

Astronuc

Staff Emeritus
It depends on the acceleration of the electron, which depends on the velocity of the electron and intensity of the magnetic field. The velocity (and kinetic energy) of electrons can be a continuous function.

3. Sep 11, 2009

CT03

Are you saying that if an electron have enough energy, it can produce a photon with a wide range of spectrum when accelerated? I thought a photon can only have a discrete amount of energy and therefore a specific wavelength.

4. Sep 12, 2009

sophiecentaur

The energy of an electron may have discrete values - as when it is 'orbiting' the nucleus of an atom (the Hydrogen Atom is the example everyone starts with. Then it is part of a system, and not on its own.

If you have an electron in a dense material, where there are many atoms around it, then it may have a continuous range of energies (a 'band'). Also, when an electron is 'free' of any nearby charges, it can take a continuum of energy values. You can make it accelerate by giving it a circular path and it can radiate energy. This "synchrotron' radiation can have photons with a range of energies. This is 'classical behaviour' and, was one of the initial problems when trying to build a model of the atom involving orbiting electrons, which 'should' be radiating all the time, but they don't. It required quantum theory to sort it out.
So it is only when an electron has particular quantised energy states (in a system involving other charged particles) that the photons need to have fixed energies. (Each individual photon can, of course, only have one energy value).

5. Sep 12, 2009

Bob S

Hi CT03-
Synchrotron radiation radiation comes from free high energy electrons (usually over 1 GeV) circulating in synchrotron accelerators and storage rings being transversely deflected (accelerated) by strong magnetic fields. The transverse acceleration is conceptually similar to bremsstrahlung from nuclear Coulomb scattering, except the accelerating force is weaker, and the synchrotron radiation is similar in energy to conventional x-rays. The initial and final states of the electrons are not quantized, and the x-ray spectrum is continuous.
Bob S

6. Sep 12, 2009

CT03

Hang on, if all the electrons in a synchrotron got accelerated in the same condition, doesn't that mean they have the same energy? if so shouldn't they produce photons with the same energy range?

Last edited: Sep 12, 2009
7. Sep 12, 2009

Bob S

Hi CT03
See the example after equation 8,71 in
http://geant4.web.cern.ch/geant4/UserDocumentation/UsersGuides/PhysicsReferenceManual/BackupVersions/V9.0/html/node46.html [Broken]
A 10-GeV electron in a 1 Tesla field produces photons with a critical (median) energy of 66.5 KeV.
Bob S

Last edited by a moderator: May 4, 2017
8. Sep 12, 2009

CT03

thanks guys. I think i got it.