Abstract

The interaction of radiation (X-rays or electrons) with matter is of interest to a wide range of areas, including: surface physics, biomedical imaging, radiobiology and astrophysics. In the case of complex, disordered, soft targets such as biological tissue, the interaction physics is complicated by random scatterings, particularly by electrons. At very low energies (< 100 eV), electrons undergo multiple elastic scattering, but can also scatter inelastically off constituent atoms and molecules of the biological target, resulting in excitations and ionizations. Electron energy losses are determined by the dielectric response of the target and the differential interaction cross-section is usually calculated from scattering theory to within the first Born approximation. On a sub-cellular level, low-energy electrons are known to cause DNA damage and subsequent cell death by two methods: 1. directly, through excitation/ionization of sites in the DNA itself, causing lesions such as single or double strand breaks; or 2. indirectly, by producing highly reactive radicals in the surrounding water molecules, which then react with the DNA . Cell irradiation experiments have revealed that in some cases, cells not directly exposed to radiation, but in contact with irradiated cells, can be killed. This bystander phenomenon remains unexplained. In this talk, I will return to the basic physics of inelastic electron scattering in condensed matter and explore the possibility that plasmon excitations propagate between adjacent cells to trigger the biochemical signalling responsible for the DNA damage and subsequent death of cells that are not directly exposed to radiation.