Electron Emission from Fast Proton and Carbon Ion Interactions with Gold Nanoparticles and Amorphous Solid Water

Abstract

Widely used in the treatment of cancer, radiation therapy delivers a lethal dose of energy to malignant tissue. Modeling the deposition of energy in the interactions of the radiation with biological material is important to accurately predict the dosimetry and the subsequent biological outcomes. Recently, nanoparticles have been observed to increase the effective damage during radiation therapy. In this study, charged particle interactions with biological materials were studied to model energy deposition and electron transport, as well as a comparison study of fast ion interactions with gold nanoparticles acting as radiosensitizers. Electron emission from metal and hydrated metal surfaces was measured for irradiation by protons and carbon ions in an energy range of maximum energy deposition, 1 to 6 MeV (near the so-called Bragg peak). Doubly differential electron emission yields were measured under ultra-high vacuum conditions using the spectroscopic technique time-of-flight analysis for low-energy electrons. This study included targets that are relevant for biological modeling, such as amorphous solid water, as well as for nanoparticle radiosensitizers, such as gold nanostructures, for which surface plasmon resonances have been proposed to contribute to the secondary electron emission.