Exercise: Insert a sample

1. Now, insert a V_sample() component (Vanadium, scatters in all directions) after the last PSD_monitor and L_monitor. Insert a Beamstop component after the sample, e.g. AT (0,0,0.5) RELATIVE sample. At the same position as the sample, insert a PSD_monitor_4PI_log component of radius 1.0 m., located AT (0,0,0) RELATIVE to your sample. Read the documentation for details on input parameters. Run a simulation. Notice the number of hits.
2. Restrict the solid angle of scattering from the vanadium sample, focus on the PSD_monitor_4PI_log by using target_x=1 and e.g. focus_r=0.2 as input parameter to the sample. Run a simulation. Notice the number of hits. Improvement?