Angular distribution of electrons behind barriers comparable to the extrapolated range

A study is reported of the angular distribution of monoenergetic electrons from a betatron which have traversed barriers of Al, Cu, and Pb with thicknesses reaching the extrapolated range. The initial electron energy is in the range 3-8 MeV. The experimental results agree well with Monte Carlo calculations carried out for identical calculations and with the results of earlier work for smaller barriers. The half-width of the electron angular distribution, increasing with increasing barrier thickness, reaches a nearly constant value, while the distribution itself corresponds to the laws of complete diffusion, i. e., converts into a distribution similar to cos²Θ. As the thickness of the absorbers is increased further, the half-width decreases and the distribution becomes narrower, due to the penetration far into the absorbers of electrons which have been scattered predominantly in the forward direction.