Pulse Radiolysis in Imaging Sciences: Silver, Silver Halides, and Other Clusters

Abstract

Pulse radiolysis has been utilized over the last three decades to study a variety of physical and chemical systems, including those relevant to imaging processes. In this overview, we outline the similarities between photolysis and radiolysis and highlight the differences. In particular, we focus on the time-resolved variants of the two disciplines: pulse radiolysis versus flash photolysis. The strength (and weakness) of the radiolytic techniques is their nonspecificity; the energy is always absorbed by the majority medium, the solvent and not the solute. Therefore, once thermalization occurs (≪ 1 ps), the primary reactive intermediates are the same regardless of the solute. From this time on, the chemistry that follows is the chemistry of radicals, radical ions, excited states, metal ions at unstable oxidation state, and other reactive molecular products such as metallic and semiconductor clusters. Thus, radiation chemistry principles that were developed for one discipline are easily transportable to another. The pulse radiolysis technique with a wide arsenal of detection methodologies is currently used to identify short-lived intermediates and to determine their kinetic and thermodynamic properties. Together these studies provide mechanistic insight into the behavior of many chemical and physical systems. We demonstrate the utility of the approach in several areas of interest to imaging sciences, in particular, clustering of silver atoms, growth of silver halides, and medium effects on these systems. Other systems of relevance to imaging sciences include reactivity and redox potentials of quinone and one-electron reduced/oxidized dyes.