An 'electron tree' produced in a block of plastic (15 cm square by 2.5 cm thick) by a beam of electrons. The electrons initially penetrate about 0.5 cm into the block and stop. As the number of electrons builds up, however, their mutual electric repulsion begins to force them apart. If the beam is switched off before this happens, a subsequent small tap to the block with a metal punch releases the electrons suddenly and they shoot out, rather like lightning, leaving a pattern of tracks that becomes 'frozen' in the plastic.
Model release not required. Property release not required.