STOPPING POWER OF THIN ALUMINUM FOILS FOR 12 TO 127 KEV ELECTRONS

Abstract

The stopping power of aluminum for electrons having energies of 10 to 125 kev was studied by measuring the average energy loss directly by calorimetric means. Two differert aluminum foils were studied of thicknesses 50.3 and 107.8 mu g/cm/sup 2/. At these thicknesses the scattering was not excessive for the incident electron energies used. The maximum path length correction was 20.6%. This was for the thickest foil and lowest incident electron energy. The foils were evaporated foils evaporated rapidly so that their thicknesses were uniform. The maximum measured energy loss was 2.5% of the incident energy and was found for the thicker foil and lowest energy. The minimum measured energy loss was 0.28% of the incident energy. This was for the thinner foil and maximum incident energy. The experimental results gave excellent agreement with Bethe's stoplength corrections were made. Since the stopping power of aluminum, according to theory, then any aluminum oxide coating on the foils would not be expected to affect the results significantly. On the basis of these experimental results, it appears likely that Bethe's stopping power theory is accurate for the energy range studied and for light materials. This is to be expected in that the beam energy was always more than five times the ionization potential of the deepest electron shell (K shell ionization potential is 1500 volts in Al). (auth)