PULSE-RADIOLYSIS IN IMAGING SCIENCES - SILVER, SILVER-HALIDES, AND OTHER CLUSTERS

Pulse radiolysis has been utilized over the last three decades to stud y a variety of physical and chemical systems, including those relevant to imaging processes. In this overview, we outline the similarities b etween photolysis and radiolysis and highlight the differences. In par ticular, we focus on the time-resolved variants of the two disciplines : pulse radiolysis versus gash photolysis. The strength (and weakness) of the radiolytic techniques is their nonspecificity; the energy is a lways absorbed by the majority medium, the solvent and not the solute. Therefore, once thermalization occurs (much less than 1 ps), the prim ary 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 semicondu ctor clusters. Thus, radiation chemistry principles that were develope d for one discipline are easily transportable to another. The pulse ra diolysis technique with a wide arsenal of detection methodologies is c urrently used to identify short-lived intermediates and to determine t heir kinetic and thermodynamic properties. Together these studies prov ide mechanistic insight into the? behavior of many chemical and physic al systems. We demonstrate the utility of the approach in several area s 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.