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The cascade of electrons generated by a single electron of energy 500, 1.5, 5 and 8 keV in a urea crystal (CON2H4) as calculated by molecular dynamics code [40,41]. The number of secondary electrons generated is plotted as a function of time after the photon absorption event. After 100 fs, there is an electron generated per 21 eV of absorbed energy. The majority of secondary electrons are created in less than 20 fs. (Online version in colour.)
