On jeudi 31 mai 2007, Murray, James W wrote:
> While we are talking about X-ray scattering, I have another question. If an
> X-ray is elastically scattered from an electron at an angle theta, its
> energy is the same is the incoming X-ray. However, the momentum is not the
> same, as it now has a component in a perpendicular direction (see fig
> below). As I don't believe that the conservation of momentum really is
> violated, what is the source of the discrepancy?
You cannot correctly describe photon-electron interactions using classical
mechanics. One reason is that the energy (among over properties) of the
electron is quantified, so the photon cannot transfer an arbitrary amount of
energy/momentum to the electron. So you'd have to consider the interaction
between the photon and everything it is bound with (atom, lattice..)
Incidentally, I think the classical delta(lambda) formula for Compton
scattering is computed for a _free_ electron.
Vincent
--
Vincent Favre-Nicolin
Université Joseph Fourier
