experiments_10 - Physics 432 Modern Physics Laboratory...

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Physics 432: Modern Physics Laboratory – Atomic and Molecular Physics Experiments List 1 Optical Spectrum of Hydrogen and Deuterium. Students measure the Balmer series emission lines of hydrogen and deuterium. Results of the measurements are used to derive a value of the Rydberg constant for each of the isotopes. The concept of reduced mass is introduced and the dependence of the Rydberg constant on this parameter is noted. A value for the H-D mass ratio is then derived from the values of the two Rydberg constants. Moseley’s Law and the X-ray Spectra of Atoms. Students measure the x-ray emission lines of multi-electron atoms using a high resolution solid state detector. They learn how the simple physics of the hydrogen atom is generalized to describe the major features of x-ray spectra for Z > 1. Students record the spectra from several samples of unknown composition, thus seeing first-hand how x-ray fluorescence can be used to determine the elemental composition of such samples. They are introduced to the physics of solid state detectors, thus acquiring insight into the remarkable resolving power of these devices. Hanle Effect. The Hanle effect in mercury atoms is used to make a Doppler-free measurement of the lifetime of the first excited state. Light from a secondary mercury source is shown onto a primary mercury vapor cell located in a slowly varying magnetic field. This field induces a Larmor precession in the excited atoms, and as they decay to the ground state the precession results in a time varying spatial distribution of the decay radiation. The magnitude of the decay radiation is measured as a function of magnetic field strength. The data are fit to a Lorentzian lineshape, thus allowing the students to determine the lifetime as one of the fitting parameters. For many decades this method was the only Doppler-free way to measure atomic lifetimes. Phase-sensitive Detection. In this exercise, students are introduced to the so called “lock-in” detector, one of the experimentalist’s most useful and powerful tools for recovering signals otherwise hopelessly buried in noise. The “signal” of interest is generated by a light emitting diode (LED)
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