PHY213_Chapter27_Sec4to8

PHY213_Chapter27_Sec4to8 - Chapter 27 Quantum Physics...

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Chapter 27 Quantum Physics
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General Physics Quantum Physics II Sections 4–8
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General Physics Diffraction of X-rays by Crystals Diffraction of x-rays can occur if the spacing between the lines is approximately equal to the wavelength of the x-ray radiation The regular array of atoms in a crystal can act as a three-dimensional grating for diffracting x-rays
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General Physics Schematic for X-ray Diffraction A beam of x-rays with a continuous range of wavelengths is incident on the crystal The diffracted radiation is very intense in certain directions These directions correspond to constructive interference from waves reflected from the layers of the crystal The diffraction pattern is detected by photographic film The array of spots is called a Laue pattern The crystal structure is determined by analyzing the positions and intensities of the various spots
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General Physics Bragg’s Law The beam reflected from the lower surface travels farther than the one reflected from the upper surface If the path difference equals some integral multiple of the wavelength, constructive interference occurs Bragg’s Law gives the conditions for constructive interference 2 d sin θ = m λ, m = 1, 2, 3…
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General Physics The main technique used to determine the molecular structure of proteins, DNA, and RNA is x-ray diffraction using x-rays of wavelength of about 0.1 nm
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General Physics Arthur Holly Compton 1892 – 1962 Discovered the Compton effect Worked with cosmic rays Director of Laboratory at University of Chicago Shared Nobel Prize in 1927
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General Physics The Compton Effect Compton directed a beam of x-rays toward a block of graphite He found that the scattered x-rays had a slightly longer wavelength that the incident x-rays This means they also had less energy The amount of energy reduction depended on the angle at which the x-rays were scattered The change in wavelength is called the Compton shift
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General Physics Compton Scattering Compton assumed the photons acted like particles in collisions Energy and momentum
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PHY213_Chapter27_Sec4to8 - Chapter 27 Quantum Physics...

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