Final PhD Seminar

Development of an annihilation radiation broadening experiment applied to spacecraft relevant materials

Mr Jacob Hughes
Pasma Research Laboratory ANU

Studying and understanding the internal structure of materials is key to development of device quality materials with well-defined electrical and mechanical properties. More and more modern materials for highly optimised applications are manufactured material composites, or processed in some way. To understand macroscopic properties exhibited by these materials, often atomic or nano scale changes need to be characterised and understood, as they can be the drivers for these effects.

Positron annihilation spectroscopy is an established analytical technique used to investigate the internal structure of materials, as the different techniques are sensitive at the molecular (sub-nanometre) level and non-destructive. Developing high quality positron spectroscopy experiments can help us to understand the evolution of materials over time in damaging environments, or precisely monitor material behaviour during fabrication and processing. Using the information gained from positron annihilation spectroscopy can lead to performance improvement in devices and materials applications.

At the Australian National University the positron research group has been using positron annihilation lifetime spectroscopy (PALS) which extracts information about defect sizes in materials through the time taken for an implanted positron to annihilate in a material. My contribution to the experimental programme of the laboratory was to implement the complementary technique of Doppler broadening of annihilation radiation (DBAR), which provides the additional ability to investigate the chemical environment at defect sites within a material. 

The successful implementation of the DBAR experiment was used in combination with the existing PALS experiment to examine the damage effects in Kapton polyimide, which had been damaged through ion implantation and exposure to plasma. The goal of this damage study was to investigate the effects of damage which could occur in long term space missions, with components from satellites or spacecraft interacting with trapped ion plasmas inside the Earth’s magnetic field, planetary atmospheres, and the solar wind. Kapton was chosen as the material to damage as it is used extensively as a thermal and electrical insulator.

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