Extended Lab Projects

NOTE:
If links below to resources are dead check the Google Drive folder for this course: here

Inelastic electron-atom scattering: Franck-Hertz Experiment

This experiment provided evidence of the quantized energy states of atoms in the very early days of quantum ideas, winning the 1925 Nobel prize for Franck and Hertz. Electrons emitted by a hot filament in a partial vacuum are accelerated by an applied voltage and directed toward a collecting plate. A clever arrangement of additional voltages on electrical grids limits those electrons reaching the collector to only the fastest by turning away slower electrons. When the tube is heated, liquid mercury in the tube vaporizes and the electrons traveling through the tube can collide with the Hg atoms in the vapor. These collisions might be elastic or inelastic - i.e. the kinetic energy of the electron before and after may be different. At the atomic level there needs to be a mechanism for the electron to transfer energy to the Hg atom. Ionization is one mechanism for an inelastic collision. A gentler mechanism for energy transfer is to excite one or more electrons in the Hg atom, changing the electron configuration from the ground state to an excited state, instead of stripping it completely. Electrons passing through the tube that experience one of these collisions before reaching the collector no longer have enough energy to reach the collector, and a decrease in the measured electron current through the tube is the consequence.
The objective of this project is to use LabVIEW, a programmable voltage supply and high quality programmable pico-ammeter to implement a version of the experiment that relies less on black-box controller technology and provides more explicit control of the accelerating voltage and a calibrated measurement of the observed current. With these implemented, make measurements of the I(V) characteristic of the Franck-Hertz tube and verify the reported excitation.
There is also a large parameter space for exploration beyond the basic measurement - involving the temperature of the system (which controls the pressure of the mercury vapor), rate of voltage sweep, cathode heating, and counter- or retarding voltage, on the quality of the I(V) curves.

Pulsed NMR

The physics of nuclear magnetic resonance (NMR) is at the core of magnetic resonance imaging (MRI) widely used in medicine. In pulsed NMR, short bursts of radio frequency magnetic fields are used to manipulate magnetic moments that are aligned by a constant magnetic field of a permanent magnet. In this case the magnetic moments are the protons in hydrogen atoms, and NMR detects their collective motion in response to the pulsed RF fields through the induced voltages they produce by rapid precession about the static magnetic field. This experiment will provide experience and understanding of the basic physics of magnetic resonance techniques. The behavior of the spins is governed by two characteristic times: the timescale for spins to exchange energy with each other - the spin-spin relaxation time (T2), and the time for interaction of a spin with its surrounding environment, the spin-lattice relaxation time (T1). These times can be measured in this experiment by fitting data collected.

Atomic Spectroscopy via Diode Lasers

A precision measurement of the splitting of electronic energy levels in rubidium using absorbtion of tuned laser light passing through rubidium vapor. The brief intro link to the right is a good description of the basic physics and experiment. Extend the measurements to investigate the effects of magnetic field via the Zeeeman effect.