Neutron Scattering Facilities at the Research Reactor DR3

DR3 is a heavy-water-moderated 10 MW thermal neutron research reactor. The 26 fuel elements contain 2.5-3.5 kg uranium enriched to less than 20% "2"3"5U. Neutron beams emerge from four horizontal through-tubes tangential to the reactor core. Two of the horizontal tubes are used for neutron scattering experiments in the field of materials research.

The vertical tubes are predominantly used for isotope production and materials testing. The thermal neutron flux is about 3.5x10"1"3 n/cm"2/s in the centre of the 7-inch diameter horizontal through-tubes. The thermal neutron flux in equilibrium with the D_2O moderator (50 deg. C) has a nearly Maxwellian distribution peaking at 1.1 A.

At the maximum flux position in the two horizontal through-tubes used for materials research are installed scatterers designed with a considerably higher scattering power for thermal neutrons than for fast neutrons and #gamma#-rays. The scatterer is either a 10 mm slab of light water, providing a nearly thermal Maxweellian spectrum at the beam port, or a chamber filled with supercritical hydrogen gas at 16 atmospheres and 38 K, a so-called cold neutron source.

The spectrum from a cold source has a considerable flux enhancement in the long wavelength region when compared to the thermal water scatterer. Neutron beams are available for materials research from two thermal and two cold beam ports in the Reactor Hall. One of the cold beams is shared with a 20 meter long cold-neutron guide-tube which provides three beam ports in a separate building, the Neutron House, with could neutrons.

Only neutrons that have undergone total reflection from the Ni-coated glass plates in the bent guide-tube arrive at the end of the guide tube in the Neutron House. The angle of total reflection is proportional to the neutron wavelength.