spectroscopy, hence the rates of reactions can be determined. This allows the relative abilities of substances to react with the reactive species generated by the action of radiation on the solvent (commonly water) to be measured. This experiment is known as pulse radiolysis which is closely related to flash photolysis. In the latter experiment the sample is excited by a pulse of light to examine the decay of the excited states by spectroscopy; sometimes the formation of new compounds can be investigated. Flash photolysis experiments have led to a better understanding of the effects of halogen-containing compounds upon the ozone layer. Chemosensor The SAW chemosensor is nonionic and nonspecific. It directly measures the total mass of each chemical compound as it exits the gas chromatography column and condenses on the crystal surface, thus causing a change in the fundamental acoustic frequency of the crystal. Odor concentration is directly measured with this integrating type of detector. Column flux is obtained from a microprocessor that continuously calculates the derivative of the SAW frequency. See also Radiolysis Milton Burton References Nuclear chemistry