- 1.3 -


        For a steady state neutron population, the first term of (2.1) is zero. This gives the steady state

Boltzmann equation for which there are many analytical and numerical methods for obtaining solutions. Exact and approximate solutions which have been obtained for solid core reactors are numerous and will not be presented here. A qualitative description of the usual treatment of the steady state Boltzmann equation will demonstrate that modifications are necessary, in order to properly describe neutrons in a plasma core reactor. When applying the Boltzmann equation to neutrons in a solid core reactor, the usual procedure is to classify neutrons as either epithermal or thermal, according to their energy. The high energy epithermal group includes those neutrons which are emitted at fission energies (average fission energy = 2 MeV) and slowed down to some thermal energy boundary (usually taken as 1 eV to 2 eV). Thermal neutrons are those which have slowed down and are in approximate thermal equilibrium at some characteristic temperature, T, of the medium. Thus the thermal energy range extends from zero to a few eV.

        In the third, fourth, and fifth terms of (2.1), the neutron speed v (or v'), appearing in the macroscopic cross sections is the relative speed between neutron and nucleus. Since solid core reactors typically operate with coolant temperatures in the 500'K to 6001K range (corresponding to