  This article is devoted to the design of importance sampling method for the
Monte Carlo simulation of a linear transport equation. This model is of great
importance in the simulation of inertial confinement fusion experiments. Our
method is restricted to a spherically symmetric idealized design : an outer
sphere emitting radiation towards an inner sphere, which in practice should be
thought of as the hohlraum and the fusion capsule, respectively. We compute the
importance function as the solution of the corresponding stationary adjoint
problem. Doing so, we have an important reduction of the variance (by a factor
50 to 100), with a moderate increase of computational cost (by a factor 2 to
8).
