Added Cosine for Source

Added the cosine of the direction in the source term.  In addition I am
using a 30% LiF compound (I just uncommented out the 10% LiF material).
XSDRN XNF Found

The XNF (source strength) for the XSDRN calculation was set to be 1.0,
and the convergence parameters were set.  These values create a
moderately accurate simulation (thought there is a little scaling
issues).