The thermal neutron beam from the reactor is divided into two parallel beams, one for D2B, the other for D20.
The D20 beam first reaches one of its four monochromators.
The monochromatic beam leaves the monochromator shielding by one of its five take-off ports, each offering a different instrument resolution.
It then reaches the sample (usually a cylinder of powder in a furnace or in a cryostat) which diffracts it in many directions.
The diffracted beams are simultaneously counted by the large microstrip multidetector.
The counts are accumulated during a certain time to give a powder diffraction pattern with a suitable intensity.