6.Al5 observed to leave the nucleus. This number of new particles is called the multiplicity and depends, to first order, on the energy of the incident particle. There is not yet total agreement as to the exact form of the multiplicity function, but most workers use one in which the multiplicity goes as El/ 4 _ Several other things are known about the nucleon-nucleus collisions: 1) approximately .8 of the outgoing particles are pions; 2) the neutral/charged pion ratio is .4 ~ .03; 3) most of the other outgoing particles are nucleons; and 4) a nucleon will leave a collision with a nucleus with about .56 of its original energy. Typical spectra of resuiting particles are known, and have to be considered. After the first collisions there are pions in the beam. When these collide with nuclei they do it inelastically, but otherwise the results are similar. When they do not hit anything and decay, the charged pions create muons and the IT 0 's create photon pairs. Once again spectra are known, and must be considered. Muons are like heavy electrons. Being leptons, they do not engage in nuclear interactions. They have a mean lifetime of about 2xl0-G seconds and decay into electrons. Until then they slow down mostly by ionization and somewhat by radiation. Electrons slow down by both ionization and radiation. The ratio of radiation to ionization energy loss per unit path length is approximately given by the simple formula EZ/800 where Eis the electron kinetic energy in MeV and Z is the atomic number of the target medium (6.A6). From this formula one may see that electrons will slow down mostly by radiation. This radiation is ca~led bremsstrahlung. The resulting photons can get stopped by either electronpositron production, the Compton effect, or photoionization. In general they will produce pairs, which produce more photons, etc., in a cascade effect. The theory behind this is known as electron shower theory, and was first described as a cohesive topic by Rossi and Greisen. Fortunately, the properties of electron showers can be described compactly without having to do detailed event by event analysis.
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