Chapter5_7 - PHY3063 R D Field The Davidson-Germer...

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PHY3063 R. D. Field Department of Physics Chapter5_7.doc University of Florida The Davidson-Germer Experiment Bragg X-Ray Scattering ( photons ): Consider the scattering ( or reflection ) of X- rays from two adjacent planes of atoms (called Bragg planes). To a good approximation the path length difference between ray 1 and ray 2 is, φ sin 2 1 2 d r r r = = , where d is the atomic spacing and φ is the “grazing” angle. Thus maximal constructive interference will occur at K , 2 , 1 , 0 2 sin ± ± = = m d m λ with the 1 st order maximum at d 2 sin 1 = . Davidson-Germer ( electrons instead of photons ): The first evidence of De Broglie’s hypothesis came in 1925 when Davidson and Germer scattered electrons off a Ni crystal. The spacing d for Ni was known from X-ray scattering to be 0.092 nm . Davidson and Germer used with a kinetic energy of 54 eV . The De Broglie wavelength of an electron with a given kinetic energy is
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