Absorption of 20-eV to 50,000-eV Electron Beams in Air and Plastic

Absorption in air and plastic of 20-eV to 50,000-eV monoenergetic electron beams was studied. A cylindrical ionization chamber operated at 10^-3 to 250 torr was used to measure absorption in air. The average energy expended per ion pair, W̄, was found to increase, with decreasing electron energy, from 33.5 eV/ion pair at 10,000 eV, to 52 eV/ion pair at 100 eV, to 74 eV/ion pair at 20 eV. Electrons transmitted and reflected by plastic foils and the ionization produced by the electrons were determined for foils from <tex-math>$0.24\ \mu {\rm g}/{\rm cm}^{2}$</tex-math> to <tex-math>$5,240\ \mu {\rm g}/{\rm cm}^{2}$</tex-math>. The electron range, R, in units of 100 μ g/ cm² (equivalent to microns at unit density) for air and plastic was found to depend on electron energy, E, in keV, as <tex-math>$R=0.0431(E+0.367)^{1.77}-0.007$</tex-math>, for E between 20 eV and 100-keV. A corresponding stopping power, dE/dX, in <tex-math>${\rm keV}\ {\rm cm}^{2}$</tex-math> per 100 μg was found to fit the relation <tex-math>$dE/dX=13.05(E+0.367)^{-0.771}$</tex-math>. Estimates were made of the energy transmitted, reflected, and locally absorbed for 150-eV to 50,000-eV electron beams in collodion. Particle energy losses of 100 keV per micron of absorber thickness were determined for electron energies below 500 eV.