# Which is bigger photon or electron

## Physics compact basic knowledge 8, textbook

Theory of Relativity 21 18 Theory of Relativity RG 8.1 and G 8.1 Compton-EŽekt (Compton scattering) 0 ° 10 ° 20 ° 30 ° 40 ° 50 ° 60 ° 70 ° 80 ° 90 ° 100 ° 10 ° 20 ° Scintillator scatter body radiation source for X-ray or γ Radiation Compton established the following: Photons of the X-ray radiation are scattered by the weakly bound electrons and give off part of their energy and their momentum to electrons. A smaller pulse of the photons corresponds to a larger wavelength. Compton determined the change in wavelength both mathematically and experimentally and found a good agreement between measurement and theory. Assuming that energy and momentum are preserved in their relativistic form, the change in the wavelength of the scattered photons can be calculated as a function of the scattering angle: D λ = h ______ m 0 ∙ c 0 ∙ (1− cos θ) D λ ... Change of the wavelength with Compton scattering h… Planck's quantum of action me… rest mass of the electron c 0… vacuum speed of light i… scattering angle Note: D λ does not depend on the wavelength of the radiation or on the scattering material. The expression h _____ (m e ∙ c 0) is called the Compton wavelength of the electron and plays an essential role in determining the range of forces. A1 State the scattering angles for which particularly large changes in the wavelength are to be expected! A2 Describe and justify the prerequisites that are included in Compton's scattering formula and are thus underpinned by Compton's experiments! Calculate the formula! A3 Name examples in which light shows the character of waves or particles! A4 Describe the wavelength for which you expect a particularly large energy exchange between photon and electron! 21.6.4 Fig. 18.1 In 1922 Arthur Compton carried out the following experiment for the first time. He bombarded graphite with X-rays and examined the scattered radiation that occurred. W1 W2 W1 W1 Pair production, pair annihilation If an energetic photon gets into the strong electric field of an atomic nucleus, it can happen that an electron and a positron are created (pair creation). The positron has the same mass as the electron, but has a positive electrical charge - the positron is the electron's antiparticle. Electron Positron Atomic nucleus Photon Fig. 18.2 Schematic representation of pair generation When pair generation occurs, radiation energy changes into rest energy, since a photon has no rest mass, but the two generated elementary particles do. The energy of the photon must at least correspond to the rest energy of the two particles: 1.022 MeV. The excess energy after the conversion remains in the kinetic energy of the particles. A5 Calculate the minimum energy for the creation of an e - e + pair with the help of the rest mass of the two particles! A6 Explain why a single electron cannot be generated from a photon! (Note: conservation of energy, conservation of momentum) Note: To research the smallest components of matter, a similar process is used: Energy (mostly kinetic energy) is converted into rest energy (m 0 ∙ c 0 2) by new elementary particles . In pair annihilation, a particle and an antiparticle collide and disintegrate. Your resting energy is converted into radiation energy. If an electron and a positron meet at low speed, two photons with an energy of 511 keV each arise. 21.6.5 W1 S1 Fig. 18.3 Schematic representation of the annihilation For testing purposes only - property of the publisher öbv