A fictitious slab with vanishing critical thickness

Abstract

Abstract In one-speed neutron transport theory, it is shown that a fictitious anisotropic fission and scattering kernel with an extreme forward bias would give a critical slab thickness varying non-monotonically with anisotropy. For this particular kernel, the critical thickness increases first with increasing forward bias but decreases later and vanishes at a pertain critical anisotropy. This is a geometrical effect which may be understood by considering the variation of the angular distribution with effectively increasing multiplicity.