Measurement of multiple scattering of 13 and 20 MeV electrons by thin foils.

To model the transport of electrons through material requires knowledge of how the electrons lose energy and scatter. Theoretical models are used to describe electron energy loss and scatter and these models are supported by a limited amount of measured data. The purpose of this work was to obtain additional data that can be used to test models of electron scattering. Measurements were carried out using 13 and 20 MeV pencil beams of electrons produced by the National Research Council of Canada research accelerator. The electron fluence was measured at several angular positions from 0 degree to 90 degrees for scattering foils of different thicknesses and with atomic numbers ranging from 4 to 79. The angle, theta 1/e at which the fluence has decreased to 1/e of its value on the central axis was used to characterize the distributions. Measured values of theta 1/e ranged from 1.5 degrees to 8 degrees with a typical uncertainty of about 1%. Distributions calculated using the EGSnrc Monte Carlo code were compared to the measured distributions. In general, the calculated distributions are narrower than the measured ones. Typically, the difference between the measured and calculated values of theta 1/e is about 1.5%, with the maximum difference being 4%. The measured and calculated distributions are related through a simple scaling of the angle, indicating that they have the same shape. No significant trends with atomic number were observed.