High-energy photons of 1.022 MeV and above may bombard the nucleus and cause an electron and a positron to be formed, a process called pair production even-higher-energy photons (beyond a threshold energy of at least 1.670 MeV, depending on the nuclei involved), can eject a nucleon or alpha particle from the nucleus in a process called photodisintegration. At energies of a few eV to a few keV, corresponding to visible light through soft X-rays, a photon can be completely absorbed and its energy can eject an electron from its host atom, a process known as the photoelectric effect.
Compton scattering verification#
Experimental verification of momentum conservation in individual Compton scattering processes by Bothe and Geiger as well as by Compton and Simon has been important in disproving the BKS theory.Ĭompton scattering is one of four competing processes when photons interact with matter.
Compton scattering free#
In this scenario, the electron is treated as free or loosely bound. If the scattered photon still has enough energy, the process may be repeated. 2, the interaction between an electron and a photon results in the electron being given part of the energy (making it recoil), and a photon of the remaining energy being emitted in a different direction from the original, so that the overall momentum of the system is also conserved. Compton's experiment convinced physicists that light can be treated as a stream of particle-like objects (quanta called photons), whose energy is proportional to the light wave's frequency.Īs shown in Fig. the comment below on elastic scattering of X-rays being from that effect). Or the assumption that the electron can be treated as free is invalid resulting in the effectively infinite electron mass equal to the nuclear mass (see e.g. Thus, if we are to explain low-intensity Compton scattering, light must behave as if it consists of particles. Thomson scattering, the classical theory of an electromagnetic wave scattered by charged particles, cannot explain shifts in wavelength at low intensity: 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 is significant because it demonstrates that light cannot be explained purely as a wave phenomenon. Compton earned the 1927 Nobel Prize in Physics for the discovery. Louis and further verified by his graduate student Y. The Compton effect was observed by Arthur Holly Compton in 1923 at Washington University in St. Although nucleus Compton scattering exists, Compton scattering usually refers to the interaction involving only the electrons of an atom. The amount by which the light's wavelength changes is called the Compton shift. 1), the energy of the X ray photon (≈17 keV) was significantly larger than the binding energy of the atomic electron, so the electrons could be treated as being free after scattering. In Compton's original experiment (see Fig. The energy of a scattered photon is measured using Bragg scattering in the crystal on the right in conjunction with ionization chamber the chamber could measure total energy deposited over time, not the energy of single scattered photons.Ĭompton scattering is an example of inelastic scattering of light by a free charged particle, where the wavelength of the scattered light is different from that of the incident radiation. The slit passes X-ray photons scattered at a selected angle. Compton scattering occurs in the graphite target on the left. 1: Schematic diagram of Compton's experiment.
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