28B photons, compton eff

28B photons, compton eff - Outline Physics 1C Lecture 28B...

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5/18/2011 1 Physics 1C Lecture 28B "In quantum mechanics we have found a region of the universe where the human brain is simply unable to be comfortable." --James Trefil Outline Last time: Blackbody radiation - Planck’s solution (1918 Nobel Prize) Photoelectric effect - Einstein’s theory (1921 Nobel Prize) Today: Compton effect (1927 Nobel Prize) Quantum Dots Nature’s Use of Quantum Mechanics The Compton Effect In 1923, Arthur Compton (U of Chicago) directed a beam of x-rays toward a block of graphite He detected the scattered x-rays had a slightly longer wavelength than the incident x-rays. This means the scattered photons had less energy than the incident photons. The amount of energy the scattered photons lost depended on the angle at which the x-rays were scattered. This change in wavelength is called the Compton shift (1927 Nobel Prize). The Compton Effect To calculate the shift in wavelength, Compton assumed that the photons act like other particles in collisions. In the collisions, energy, hf, and momentum, hf/c , were conserved. The energy of the incoming photon was: After it collides it scatters by an angle θ . The Compton Effect 0.00243 e h nm mc After the collision the photon has an energy: The wavelength shift becomes: where the Compton wavelength for the electron is a constant: ' 1 cos o e h The Compton Effect Schematic diagram of Compton’s apparatus:
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28B photons, compton eff - Outline Physics 1C Lecture 28B...

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