Compton Effect
Definition and meaning of Compton Effect in chemistry.
The Compton effect is the increase in wavelength observed when X-ray or gamma-ray photons are inelastically scattered by loosely bound or free electrons in matter.
In more detail
When an incident photon collides with an electron, it transfers part of its energy and momentum to the electron, so the scattered photon emerges with lower energy and a correspondingly longer wavelength. The size of this wavelength shift, Δλ, depends only on the scattering angle θ, following the Compton formula Δλ = (h/mₑc)(1 − cos θ), independent of the incident wavelength or the scattering material. The effect was decisive evidence that electromagnetic radiation behaves as discrete particles (photons) carrying momentum, not just waves, reinforcing the emerging quantum theory of light. It remains important for understanding X-ray and gamma-ray interactions with matter, including radiation shielding and detector design.
Key facts
| Field | Physical Chemistry |
|---|---|
| Discovered by | Arthur H. Compton, 1923 |
| Governing equation | Δλ = (h/mₑc)(1 − cos θ) |
| Compton wavelength (electron) | 2.43 × 10⁻¹² m |
In 1923, Arthur Compton directed X-rays at a graphite target and found that the scattered X-rays had a longer wavelength than the incident beam, with the shift matching the angle-dependent prediction of photon-electron collision theory.
Frequently asked questions
How does the Compton effect differ from the photoelectric effect?
In the photoelectric effect a photon is completely absorbed and ejects an electron, whereas in the Compton effect the photon survives the collision but loses some energy, emerging with a longer wavelength (inelastic scattering rather than absorption).
Why does the photon's wavelength increase rather than decrease?
Because the photon transfers kinetic energy to the electron it scatters from; since photon energy E = hc/λ, a loss of energy corresponds to an increase in wavelength.