## Exercise: Source and PSD

1. Start by inserting a template instrument (Insert menu). Set up an instrument, consisting only of an Arm (keep the example 'a1' Arm instance), a Source_Maxwell_3, a PSD_monitor and an L_monitor. Read the documentation for each of the components to find the needed input parameters. For the source we will help you out, try

       COMPONENT source = Source_Maxwell_3(
           size = 0.1, l_low = 0.1, l_high = 10, dist = 10, xw = 0.01,
           yh = 0.01, T1 = 300, T2=300, T3=300, I1=1e14, I2=0, I3=0)

   Read the Source_Maxwell_3 docs using mcdoc to understand the suggested parameters. The file names for monitors, specified as character strings, should be given surrounded by double quotes ("file.dat").
2. Run a simulation and plot the results, looking at an image of the source plus the wavelength distribution of the source.
3. Narrow down the interval of wavelengths emitted from the source to e.g. l_low=0.999 and l_high=1.001. Rerun your simulation to check the effect. Reset the wavelength interval to [0.1 10] Å.
4. Estimate the solid angle covered by your PSD. Try if you can understand I, the neutron intensity in the PSD, in the two previous runs. Try running the simulation with half or double the number of neutron rays. Try also to vary the source focus area. Explain what you observe.