COMPTON EFFECT SERIES

A graphite target was bombarded with monochromatic x-rays and the wavelength of the scattered radiation was measured with a rotating crystal spectrometer. Compton's experiment convinced physicists that light can behave as a stream of particles whose energy is proportional to the frequency.Ī schematic diagram of the apparatus used by Compton is shown in the Figure below. Light must behave as if it consists of particles in order to explain the low-intensity Compton scattering. Thomson scattering, the classical theory of an electromagnetic wave scattered by charged particles, cannot explain low intensity shift in wavelength (Classically, light of sufficient intensity for the electric field to accelerate a charged particle to a relativistic speed will cause radiation-pressure recoil and an associated Doppler shift of the scattered light, but the effect would become arbitrarily small at sufficiently low light intensities regardless of wavelength.). The effect was first demonstrated in 1923 by Arthur Holly Compton (for which he received a 1927 Nobel Prize).The effect is important because it demonstrates that light cannot be explained purely as a wave phenomenon. The scattered radiation experiences a wavelength shift that cannot be explained in terms of classical wave theory, thus lending support to Einstein's photon theory.

This effect is one of many important ones for particle physicists to know when it comes to the interaction of photons with matter.The Compton effect (also called Compton scattering) is the result of a high-energy photon colliding with a target, which releases loosely bound electrons from the outer shell of the atom or molecule. It is observed at the event horizon of black holes. One example is inverse Compton scattering, where the photon gains, instead of losing, energy from matter. The Compton effect was later generalized to Compton scattering, a phenomenon which describes how photons in general interact with matter. Along with other such experiments in the early 20th century, this led to the development of quantum mechanics, which studies how matter and radiation behaves at the smallest level. This means that matter and radiation can act both as particles and as waves depending on the situation of the experiment. The Compton effect was an important piece of evidence of “ wave-particle duality“. Also, it can be seen that the wavelength is either unchanged or decreases, but never increases. This statement means that the change in wavelength is minimum and zero in the forward direction (θ = 0°) and maximum in the backward direction (θ = 180°).įor all other angles, the value is somewhere in between.

We can now describe the change in wavelength as θ is the angle at which scattering is observed. We take the initial and final wavelengths of the X-rays to be λ and λ’ respectively. cannot be created or destroyed) for these two particles together to arrive at the final expression for the change in wavelength. He used relativistic expressions for their energies and momenta.įurther, he used the fact that energy and momentum are conserved (i.e. To arrive at this, Compton studied the collision between the photon and the electron. This loss in energy is visualized by the change in wavelength.Ĭompton provided the formula in 1923. Visualizing the Compton effect as a collision between photons and electrons. When X-rays interact with electrons, the photons come and collide with the electrons, making them move.Īs in most collisions, the photon now loses some momentum to the stationary electron. It is now simpler to visualize why the wavelength changes. Since the change in wavelength could not be explained by classical mechanics, he developed an explanation that treated X-rays as though they consisted of particles called photons.

COMPTON EFFECT SERIES

Compton’s ExplanationĬompton performed his own series of experiments involving X-rays scattering off graphite at various angles. If this intensity was made low enough, they should not interact with matter, in this case electrons, and hence there would be no change in wavelength. According to classical mechanics, X-rays were waves with a certain adjustable intensity. This couldn’t be explained by classical mechanics. The experimental setup for the Compton effect. It was noticed that the scattered X-rays had a change in wavelength which depended on the angle of scattering. The experiment involved a beam of X-rays made to scatter off some form of matter.

The Compton effect was observed when X-rays were made to interact with matter.