COMP: Compton Scattering

The goal of this experiment is to measure the inelastic scattering of photons by free electrons and determine the fundamental parameter of Quantum Electrodynamics (QED) with the highest precision you can achieve. This parameter – the Fine Structure Constant αQED – measures the coupling of the QED gauge boson (the photon) to a charged spin 1/2 point fermion (the electron). Precision measurements of αQED are an important way to look for new interactions beyond the Standard Model of Particle Physics.

In this experiment, the absorption of gamma-rays by materials with various atomic numbers is measured. The total cross section for Compton scattering is determined, and a value for the fine-structure constant calculated. Arthur Compton won the 1927 Nobel Prize in Physics for his discovery of the Compton effect.

Write-Up in PDF Format or Microsoft Word Format.

(The experiment is currently located in MP245; last write-up revision: September 2018.)

Photo of student working on Compton experiment

3rd year Physics undergraduate, Asma Al-Qasimi, working on measuring the Compton Total Cross Section. Note that she very sensibly has a copy of Leo, Techniques for Nuclear and Particle Physics Experiments : a How-To Approach, open on the table in front of her to help her understand the apparatus.