Measurement of the Thermal Absorption Cross Section in Lucite Using Fermi Age Theory

The diffusion processes of neutrons in Lucite have been investigated. The mechanisms for these processes have been described as having two steps. In the first step, the fast neutrons collide with the nuclei of Lucite, losing energy until they reach thermal energies. In the second step of the diffusion process, the thermal neutrons continue to diffuse through the Lucite without any significant loss of energy until they are finally absorbed or leak out of the system. Experiments were performed to study these two processes and to estimate the absorption cross section in Lucite. The experiments yielded an average range of 6.3 ± 0.1 cm for fast neutrons slowing down to thermal energies and a thermal absorption cross section in Lucite of 0.52 ± 0.02 b.