Positrons and biomolecules - from gas phase to liquids*

Positrons interactions with biomolecules have been the subject of much research in recent years (e.g., [1]). In addition to extending theoretical models to encompass complex molecular targets, the ultimate aim is to be able to provide an improved description of positron interactions inside living systems [2]. This is important to, for instance, improve the understanding of radiation damage in Positron Emission Tomography (PET) scans. Most of the theoretical calculations to date have been for interactions with single molecules, which already presents a complicated problem for accurate descriptions of low energy collisions, thanks to the many degrees of freedom of the problem. All of the experimental work has been with molecules in the gas phase, which provides a direct test of these theories, although measurements on molecules that exist as solids at room temperature has been quite limited. 

In this presentation, I will discuss a research program that seeks to extend the experimental and theoretical work on these systems to include molecules that are typically solid at room temperature, as well as extending studies into the liquid phase, both theoretically and experimentally. The experimental work is carried out at the Australian National University, using a Surko trap and beam system [3]. Recent measurements of positron scattering from pyrazine will be presented, and compared to the most recent theoretical approaches. Plans for extending the experimental measurements to solid targets will also be discussed, along with planned measurements of positron interactions with liquid water, with the aim of testing models of positron transport in liquid and soft condensed matter. 

[1] M. J., Brunger et al., Journal of Physical and Chemical Reference Data 46, 023102 (2017)

[2] R. D. White et al., Appl. Radiat. Isot. 83, 77 (2014).

[3] J. P. Sullivan et al., Rev. Sci. Instr. 79, 113105 (2008)