Time-of-flight Apparatus

The time-of flight experiment is a typical crossed beam apparatus consisting of an electron monochromator and a gas jet, with the electron and atomic beams crossing at right angles. A Faraday cup is placed opposite the exit aperture of the electron gun to monitor the electron beam current. Various analysers have been used inside the experiment in the past, including a Hemispherical energy analyser with a channeltron detector, a large hemispherical analyser (~15 cm radius) with a Position Sensitive Detector and an earlier Time-of-flight detector (consisting of a drift tube and a channeltron).

At present, experiments are focused on studying near threshold excitation processes in atoms and molecules. We have developed a Time of Flight energy analyser and detector in order to overcome the severe problems associated with the "absolute" detection of low energy scattered electrons. Instead of using a conventional electrostatic analyser to determine the energy of scattered electrons we are using their time-of-flight between the collision volume and a detector as a measure of their energy. The detector is a large area, position-sensitive device giving us increased sensitivity. By pulsing the electron beam, and looking at the scattered electrons detected as a function of time and position, we can determine their energy and scattering angle. By comparing inealstic processes to elastic scattering, we can also determine the cross section for each process.

Centre Researchers working on this apparatus

Professor Steve Buckman, Dr. Julian Lower

Student Projects available

Vibrational and Electronic Excitation of Molecules by Positron and Electron Impact