Pair Production and photon-matter interactions Contents: Photoelectric effect Compton scattering Absorption Pair production Whiteboards.

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Presentation transcript:

Pair Production and photon-matter interactions Contents: Photoelectric effect Compton scattering Absorption Pair production Whiteboards

Photoelectric effect TOC 1.Photon knocks electron from atom 2.Photon disappears in the process

Compton Scattering TOC 1.Photon bounces off electron 2.Electron absorbs some energy 3.Photon has longer wavelength after collision

Absorption TOC 1.Photon hits electron in orbital 2.Electron moves to excited state 3.Photon disappears in the process 4.Only for photons with the right energy

Pair production TOC 1.Photon with sufficient energy passes near nucleus 2.Energy of photon turns into matter 3.Pair of matter/anti matter is created 4.Nucleus must carry off some momentum Electron m = 9.11 x kg Charge = -e Positron m = 9.11 x kg Charge = +e Help me! I’m going to be annihilated presently!

Solving pair production E = hf = hc/ E = mc 2 E - Energy m - mass c = 3.00 x 10 8 m/s 1 eV = x J So matter can turn to energy and vice versa. Example 1: What energy is needed to create a single electron in J and in MeV? (an MeV = 1 x 10 6 eV) TOC

Solving pair production E = hf = hc/ E = mc 2 E - Energy m - mass c = 3.00 x 10 8 m/s 1 eV = x J Example 2: What energy photon (in MeV) is needed to create a electron-positron pair each with a kinetic energy of.34 MeV? What is the wavelength of that photon? Photon energy = energy to create matter + kinetic energy TOC

Solving pair production E = hf = hc/ E = mc 2 E - Energy m - mass c = 3.00 x 10 8 m/s 1 eV = x J Example 3: A nm photon creates a electron positron pair. What is the kinetic energy of each particle? TOC

Whiteboards: Pair production 11 | 2 | 323 TOC

1.362 MeV W photon energy = energy to create mass + kinetic energy =.511 MeV MeV MeV MeV = MeV A photon creates a electron-positron pair each with a kinetic energy of.170 MeV. What is the energy of the photon? (in MeV)

129 MeV W Proton rest mass = 938 MeV photon energy = energy to create mass + kinetic energy 2134 MeV = 938 MeV MeV + kinetic energy kinetic energy = 258 MeV/(2 particles) = 129 MeV A 2134 MeV photon creates a proton, negatron pair, each with how much kinetic energy? (2)

666 keV W E = hf = hc/ E = hc/, = (6.626 x Js)(3.00 x 10 8 m/s)/( x m) = ( x J)/(1.602 x J/eV) = eV = 2354 keV photon energy = energy to create mass + kinetic energy 2354 keV= 511 keV keV + kinetic energy kinetic energy = 1332 keV/(2 particles) = 666 keV A photon with a wavelength of x m creates a electron- positron pair with how much kinetic energy each? (answer in keV)

Wave behaviour: So - is light a wave or a particle? Refraction Interference Diffraction Particle behaviour: Photoelectric effect Compton scattering Absorption Pair production

What is light? Complementarity - Using a variety of models to describe a phenomenon. Particle behaviour Wave behaviour Light is described totally by both wave and particle behaviour For a given experiment, light is a wave xor a particle