mgxs.h5 fixed source 100 30 10 0.0 -5.0 -5.0 40.0 5.0 5.0 1000.0 1.0 material 1 multi-group 100.0 400.0 0.0 -5.0 -5.0 40.0 5.0 5.0 flat s2 10 1 1 0.0 -5.0 -5.0 40.0 5.0 5.0 1 1 flux tracklength