AN UNDERGRADUATE EXPERIMENT ON X-RAY-SPECTRA AND MOSELEYS LAW USING ASCANNING ELECTRON-MICROSCOPE

We describe an undergraduate laboratory experiment developed for sopho more modern physics students, using the x-ray analysis feature of a sc anning electron microscope. The experiment described is a fundamental physics measurement performed with a state-of-the-art apparatus not us ually used in pedagogical physics experiments. The characteristic x-ra y spectrum of elements shows a simple progression that can be quantita tively explained by the conceptually important Bohr-Rutherford shell m odel of atomic structure. Students measure the K alpha and KP x-ray sp ectra from metals in the range of 12 less than or equal to Z less than or equal to 41. The measurements allow the verification of Moseley's law scaling of x-ray energies with atomic number and a quantitative me asure of the data's fit to the shell model. (C) 1996 American Associat ion of Physics Teachers.