Ionic Processes in High-Energy-Induced Luminescence of Liquid Organic Systems

Luminescence of dilute organic scintillators in liquid aliphatic hydrocarbon solution excited by very short pulses of x rays decays nonexponentially. In contrast, excitation by pulsed uv gives luminescence the decay law of which can be described by an exponential function. A satisfactory explanation is that under high-energy radiation, the mechanism of excitation of the scintillator involves ion recombination, while direct excitation and energy transfer play a minor role. Additives (nitrous oxide, carbon tetrachloride, piperidine) which do not affect the excited scintillator but react with charged species such as ions and electrons show a marked effect on the luminescence of the high-energy-excited systems only, a result which supports the ionic mechanism. An attempt is made, on the basis of simplified assumptions, to derive from the luminescence intensity–time curves a distribution function of the secondary electrons released by the interaction of the x rays with the system.