Positron Annihilation Lifetime Spectroscopy (PALS) has become a powerful tool in the analysis of material properties at the nano-scale. This project will involve using the high energy materials beamline to investigate nano-porosity and vacancies in a variety of materials ranging from polymers and semiconductors to naturally occurring and man made minerals. Due to the nature of this research program there is a large scope for students to design and implement their own project which can be done in collaboration with other facilities such as those at the Australian Nuclear Science and Technology Organisation.

At the ANU we have developed two new positron beam lines for studies of positron interactions with atoms, molecules and materials. One of the beam lines is designed for high energy (0.5 - 20 keV) studies of materials. In this apparatus, a fast pulse of positrons is injected into the material of interest. The injection energy determines, on average, how deep they penetrate before thermalising to low (<50 eV) energies. After thermalising the positrons annihilate, creating two 511 keV gamma rays. These gamma rays are detected and the time between their detection and the initial pulse injection is accurately measured. The lifetime of the positrons in the material is a sensitive measure of the material properties, in particular the size and distribution of open space or pores within the material.

During the project the student will develop skills in:

• Material science and condensed matter physics
• Handling positron beams and gamma ray detection
• High vacuum practice
• Working in a team environment
• Fast pulse processing and high speed data acquisition
• Data analysis and interpretation
• Computer control of experimental hardware