- 32 -


a significant correction to the relative energy, and hence to the amount of resonance absorption. At the extremely high temperatures which are being considered in the plasma core reactor, this correction may strongly influence reactor criticality and stability.

        Expanding equation (2.13) as before and retaining all terms, the relative energy is



             1              2
             E r = E + f PV N2 - 2E V z          (2.23)



where E     P v2 again denotes the relative kinetic energy

of the neutron stationary nuclei. The relative energy is now a function of all three velocity components (Vx, Vy, V z), rather than the single component Vz as in the case of solid fuel nuclei. Hence, the probability of a neutron collision with a nucleus with velocity VN = (Vx, Vy, V z) is proportional to the three dimensional Maxwellian distribution of nuclei P(VN), where



          P(V d'V          3(2 e 3/2 2/2kT 4 2dV (2.24)
             N 'N     2 M7TkT eVN MN


where V   = Vx2 + Vy2 + Vz2. The effective resonance absorption cross section for a neutron with kinetic energy E is