correction de transport

CONT: Correction de transport. Éliminer [oméga] des équations est évidemment une simplification incontestable! Mais a-t-on le droit de supposer que les neutrons sortent des collisions de façon isotrope? Ce n’est évidemment pas exact en toute rigueur, mais on constate qu’en général l’erreur due à cette hypothèse est peu importante, surtout si l’on fait une correction dite de transport consistant à remplacer la section efficace totale [oméga indice t], par la section efficace de transport […]

CONT: Transport correction. Much of the error due to the diffusion approximation comes from the assumption of isotopic scattering. (This assumption is necessary to reach the simple form of the integral transport [and] was also made to establish Fick’s law when we assume that when a neutron leaving dV had probability d[superscript 2 omega]/4[pi] of hitting dS where d[superscript 2 omega] was the solid angle under which dS is seen from the point of emission). The transport correction established from the differential form of the transport operator can compensate for most of this error. Because it is simple to introduce, it is always used in practice. It consists of replacing the total cross-section [sigma] with the so-called “transport” cross-section in the expression for the diffusion of the coefficient.