Positron Imaging Centre

Demonstration Rig

The technique of PEPT, developed at the University of Birmingham in the UK, has been applied in the demonstration video below. The Demo Rig in the video portrays the real-time ability of the detectors, and is routinely used in open days and outreach events both on and off campus.

The clockwork robot stands between 2 banks of position sensitive radiation detectors holding a small radioactive source (50 kBq of Na-22 in 2mm glass bead) in its hand. This source decays via positive beta emission (emitting a positron or anti-electron).

The emitted beta particle quickly annihilates with a normal electron, and the rest mass of the pair is converted into energy in the form of two gamma rays. These are constrained to travel back-to-back due to energy and momentum conservation.

Provided both of these gamma photons are detected a line can be joined between the two respective detection elements, along which the annihilation site must be positioned. The technique of Positron Emission Particle Tracking (PEPT) then uses a small number of these lines to accurately locate the radioactive particle in space.

On the computer screen behind the robot the data from the detector system is displayed, the green lines show each of the detected trajectories for the pairs of gamma photons. Clearly these converge at the position of the source particle; where the PEPT algorithm is used to draw a small box for each location.

Typically this technique is used to study physical and industrial systems, and can be used on opaque systems with considerable thickness of material: thus the process studied can be at industrially relevant conditions (e.g. elevated temperature and pressure). It is expected that a particle can be located at a frequency of 1kHz, with precision of around 0.5mm in 3 dimensions.