Phy433_manual_ch7 - 7 Particle Interactions with Matter...

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7 Particle Interactions with Matter Heavy charged particles such as alpha particles, protons, and muons interact with matter and lose energy mainly as a result of Coulomb forces resulting in ionization of atoms in the material. Although the strongly interacting particles can also undergo collisions with the nucleus this has lower probability and is not important at low energies (several MeV). Electrons can also collide with atomic electrons but because the masses are the same the kinematics are quite different. In addition electrons can lose energy through radiative processes (bremsstrahlung) although for low energy electrons (several MeV) that we will be concerned with this is not a very important mechanism. Gamma rays interact with matter in one of three ways: photoelectric effect, Compton scattering or pair production. The relative importance of these three processes depends on the gamma ray energy and on the material; in the region up to several MeV the first two are dominant. The operation of most particle detectors depends on the energy loss of the particle, by one or more of the above mechanisms, in its passage through the detecting medium. 7.1 Energy loss of heavy particles See appendix for a simple derivation of energy loss, dE/dx. If energy loss is expressed in terms of grams/cm 2 then the stopping power, dE/dx is nearly the same for all materials except for hydrogen (where Z/A is 1 rather than approximately 2). The range of a heavy particle of energy, E o , is defined as = 0 ) / ( o E dx dE dE R (3) Energy loss occurs through a large number of collisions with a small energy loss per
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This note was uploaded on 01/28/2012 for the course PHYSICS 433 taught by Professor Henrylubatti during the Fall '11 term at University of Washington.

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Phy433_manual_ch7 - 7 Particle Interactions with Matter...

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