Radioluminescence decay in crystalline terphenyl excited by electrons: initial structures of slow electron tracks

The track structure of an electron in condensed matter has been investigated by the analysis of the scintillation decay curves of a terphenyl crystal. The excitation has been initiated inside the crystal by Compton electrons and observed by a coincidence device which analyzes only emission corresponding to a well defined energy of the electrons. This energy was varied from 0.12 to 370 keV. The experimental variation with incident energy, of the ratio of the integrated intensities emitted in isolated zones of activation (spurs and blobs) and in short tracks is in good agreement with a computation of the various amounts of energy deposited in spurs, blobs and short tracks, taking as upper limits of the electron kinetic energy for the production of short tracks and blobs, 1 keV and 0.1 keV respectively. Furthermore the data indicate that there is no overlapping of the short tracks, at least during the first μs after irradiation. Finally, the mean energy required to form, within the spurs, a fluorescent singlet state which is not quenched by interaction with other activated species, was found to be of the order of 140 eV and the energy necessary to create a triplet state in the tracks, responsible for the delayed luminescence, was estimated to be about 10 eV. (author)