Decay Times of Fluorescent Substances Excited by High-Energy Radiation

Decay times of fluorescent light emitted by organic solutions and by onganic and inorganic solids when excited by high-energy radiation are determined under various experimental conditions. The pulse-height ratios for alpha particle and electron excitations are also found. The probabilities for radiative and nonradiative transitions of the light emitting molecule are estimated and compared with values obtained from absorption measurements. The time required for energy transfer is estimated. The ratio of pulse heights obtained under alpha -particle excitation to those obtained under electron excitation are found to be roughly the same for all organic solutions and solids despite wide variations in lifetime; also no difference in lifetime between alpha -particle and electron excitations is found. This is not explained by present theories. A new theory to explain these facts is outlined. (auth)