Three pieces of acrylic, two of them cylinders and the third rectangular, displaying the discharge pattern or “tree” produced by irradiating the acrylic with an electron beam. Electron accelerators, in addition to important industrial applications, can be used to produce an impressive form of “art”. Lucite blocks, either rectangular or cylindrical, are placed in front of a scanned electron beam. The energy of the electrons that strike the material is chosen so that the beam penetrates roughly half the thickness for flat material or one-third for cylindrical material before stopping and charging up the plastic. (This penetration is the “range of the electrons”).
The length of time required for the beam on the target (typically a few minutes) is dependent on the characteristics of the particular accelerator and of the specific plastic used. This is often found by using a smaller test piece. Following the irradiation a sharp point, which is electrically grounded, is driven a short way into the plastic with a sharp blow from a grounded hammer and an electrical discharge, very similar to a lightning strike, occurs within the plastic. The discharge paths show up as damage to the plastic and produce the beautiful “trees” seen – each one is unique. Too long an exposure of the plastic to a scanned beam can result in a spontaneous discharge to the nearest ground points and will spoil the appearance of the tree; too short a time results in very fine lines that are barely visible.
