Positrons are used in the diagnosis of human tumours, through the use of Positron Emission Tomography (PET). They are also mooted as a possible therapeutic tool (positherapy) in the treatment of tumours. This project will investigate and quantify, at the fundamental level, the interactions of positrons with a number of important biomolecules.

PET scans involve detecting the annihilation gamma rays that are produced when positrons are selectively introduced to the site of a tumour. Most of the radioactive positron emitters which are used for these purposes (eg 18F) emit high energy (~600 keV) positrons, which must thermalise, via scattering, before entering the energy regime which is favoured for annihilation (<~20 eV). Annihilation takes place either by direct means, whereby the positron picks up an electron from the surrounding medium and annihilates, or through the formation of positronium, an electron positron pair, which subsequently annihilates. Direct annihilation is only strongly favoured at very low positron energies (<1 eV) while positronium formation is typically strongest in the 5-20 eV region and is generally a process with a much larger probability.

This project will focus on measurements of fundamental scattering processes (total and elastic scattering, vibrational excitation, electronic excitation, positronium formation) using positrons. The experiments will be carried out at the ANU node of the Centre for Antimatter-Matter Studies (CAMS), using the low energy positron beamline located there. The goal is to provide benchmark cross sections for important biomolecules, ranging from H2O and simple acids, such as formic and acetic acid, to the sugars and bases that make up DNA and RNA strands. This information can then be used to build a new model for positron thermalisation and annihilation in the body, a project that is part of the broader research program within CAMS.