Two thermal neutron beams are injected from opposite directi

Two thermal neutron beams are injected from opposite directions into a thin sample of ^235U. At a given point in the sample, the beam intensities are 10^12 neutrons/cm^2sec from (be left and 2 Times 10^12 neutrons/cm^2 middot sec from the right, Compute: (a) the neutron flux and current density at this point and (b) the fission reaction rate density at this point.

Solution

Neutron flux = 1.0 e+12 + 2.0e+12 neutrons/cm²-sec

                     = 3e+12

U-235 fission corss section for thermal neutron = 505 b = 505 e-24 cm²

fission rate = 3.0e+12 *505 e-24 = 1.515 e-9 /s