In this work the neutron multiplication in a source driven subcritical nuclear system is studied for a particular physical model of symmetrical slab geometry. On both sides of a central spallation source region, bare fissile blankets are placed. The neutronics of the system is represented in terms of two-group diffusion equations. We elaborate on the development and evaluation of the multiplication factors for source and fission neutrons (k(s) and k(f)). The results are compared with the conventional multiplication factor k(eff) of the fissile system. In the present static context, k(eff) is important only from the safety point of view, whereas the other two factors are figures of merit measuring the effectiveness of a source neutron to start a fission chain and that of any one fission neutron to maintain a fading chain which further contributes to source multiplication.