About EGS: Why was EGS Developed?
When high-energy particles, in the form of electrons and/or photons hit matter, they travel through the material, interacting with atoms and their nuclei in various ways that are easily predicted by physics. The path of each particle can be modeled as a "random walk" as collisions with atoms occur with well-defined probability.
Each individual interaction can generate many more electrons and photons due to collisions as it travels through matter. This process is given the name "shower" because that is what it looks like. The picture above is a computer simulation, generated using the EGS code, showing the interactions generated by a single 1 GeV electron hitting a 2 cm thick tungsten target. Just look at all the electrons (green), positrons (red), and photons (yellow) that are generated in this shower!
EGS was developed to design safe experiments for high energy physics. By modeling these processes physicists could ensure that the shielding they installed would protect everyone around from the short-lived but intense radiation produced when an accelerator beam strikes a target. The same EGS code has been used to design detectors of this radiation and it was used in the design of most of the particle physics experiments in the 1980s.
The EGS code is capable of generating many kinds of pictures. The image above is an example showing 10 high-energy positrons (300 MeV) spread out vertically and incident from the left into liquid hydrogen in a 1-Tesla magnetic field going into the screen. Again, electrons are green, positrons are red and photons are yellow. The trajectories of the electrons are bent into spirals because of the magnetic field that is perpendicular to the page and electrons and positrons spiral in opposite directions. Photons are not affected by magnetic fields. Look at all the particles set in motion from just a few high-energy positrons!
Did you know that a magnet in your TV bends low-energy electrons to different areas of your screen to create an image?
As you could guess, predicting the combined effect of all the interactions in this process is extremely difficult using standard mathematical methods . . . but the EGS code can do it!
