The constant wavelength (CW) neutron diffractometer can be placed on one of two locations that are available at the reactor. Although one has a 20% higher thermal flux, the instrument would be better accessible at the other beam line. This practicality makes the daily operation easier, but also the installation of the (heavy) shielding at the beginning.
In Ruud’s drawing above: The (yellow) beam travels from the core to the (red) focussing monochromator which reflects 1.7AA neutrons to the (blue) sample. The scattered neutrons from the sample are counted by the (green) banana-shaped detector that is centered on the sample. The environment around the instrument is shielded from the gamma and neutron radiation by thick (grey semi-transparent) walls.