Spatial Distribution of Energy Absorbed from an Electron Beam Penetrating Aluminum

An electron beam introduced into an infinite medium is scattered and absorbed as the electrons slow down. The ionization produced by the beam in a plane air cavity perpendicular to the initial beam direction was used to measure the spatial rate of energy dissipation at various distances from the plane of incidence. At beam energies of 57, 80, 104, and 126.5 kev, agreement within a few percent on an absolute basis with the Spencer theory of electron penetration was found if the value of $W$, the average energy to make an ion pair, is taken for air to be 34 electron volts per ion pair.