# Compton Scattering

1. Sep 23, 2004

### timmyeatchips

To back me up with some of my chemistry courses this year, I picked up a quantum mechanics book that looked like it included some fairly simple introductions to quantum principles.
However, in the first chapter it used Compton scattering, the lowering in wavelength of X rays due to collision with atomic electrons, as early evidence for the existence of the photon.

My question is, how does this partial loss of energy fit in with the idea of photon energy being quantised?

2. Sep 23, 2004

### humanino

Welcome Timmy, and please let some chips for everyone

You must first be aware that it is not possible to deviate a photon, but in Compton scattering it looks like it is. Planck earlier used the formula $$E=h \nu$$ to find the good black-body radiation spectrum, both in infra-red and ultra-violet light, and this was the birth of QM. Compton used this formula and the idea that photon is a regular particle, but only in that he applied conservation of energy and momentum as in regular billard game. This allowed him to derive his $$\lambda_f-\lambda_i=\frac{h}{m_ec}\left (1-\cos(\theta)\right )$$ that explained Xrays diffraction by crystals.
See hyperphysics for instance.