43// This class is responsible for the generation of primary adjoint particle on the external surface of a user selected volume.
44// The particle are generated uniformly on the surface with the angular distribution set to a cosine law relative to normal of the surface.
45// It is equivalent to the flux going in from the surface if an isotropic flux is considered outside.
46// It uses ray tracking technique and can be applied to all kind of convex volume. Uisng the ray tracking technique the area
47// of the external surface is also computed. The area is needed to fix the weight of the primary adjoint particle.
48// At the time of the development of this class, generation of particle on volume surface and computation of surface was limited in G4,
49// therfore the general ray tracking technique was adopted. It could be now (2009) that direct method of G4VSolid could be used instead. To be checked!