The thermal neutron diffusion cooling coefficient in polyethylene

The di€usion cooling coecient C for thermal neutrons in polyethylene at 20 C has been determined theoretically. Granadaʹs Synthetic Model of the scattering law has been applied to describe the interaction of neutrons with polyethylene. Two approximations of the neutron energy distribution in finite homogeneous systems have been used. The result of the calcula- tion using a rough approximation is CB=2160 cm4 s-1. According to a more advanced form- alism which follows Nelkinʹs analysis of the neutron pulse decay in a finite medium, applying the di€usion theory with transport correction, the value obtained is C=2916 cm4 s-1