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-raysfrom two adjacent planes of atoms (called Bragg planes). To a good approximation the path length differencebetween ray 1 and ray 2 is,φsin212drrr=−=∆, where dis the atomic spacing and φis the “grazing” angle. Thus maximal constructive interference will occur at K,2,1,02sin±±==mdmλwith the 1storder maximum at d2sin1=. Davidson-Germer (electrons instead of photons): The first evidence of De Broglie’s hypothesis came in 1925when Davidson and Germerscattered electrons off a Ni crystal. The spacing dfor 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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