NEUTRON TRANSMISSION THROUGH TAPERED CHANNELS

The transmission of neutrons through a tapered channel is analyzed and the relationships among various parameters such as the distance betwe en reflections and the polar and grazing angles of a trajectory at eac h reflection are established, These relationships are used in a simula tion to study the transmission characteristics of a cylindrical tapere d channel, The transmission, the transmitted beam angular divergence a nd the number of reflections are determined for different values of th e taper angle and the incident beam divergence. The simulation results for the straight channel agree exactly with the derived analytical ex pressions, Those for the tapered channels can be described using the s ame expressions but with a lower effective critical angle. This reduce d critical angle depends on the length of the taper and on the taper a ngle. For long gentle tapers, the reduction in critical angle is equal to the reduction in channel diameter.