The HB-2 thermal neutron beam tube is situated radially relative to the reactor core, looking directly at the fuel. Two beryllium inserts are installed in the spherical tip of the beam tube to maximize the thermal neutron flux within the critical acceptance angle of the neutron scattering experiment equipment. The beam tube cavity outboard of the reactor vessel has a rectangular cross-section that converges vertically and diverges horizontally such that the aperture at the outboard window is a rectangle nominally 6-in tall by 10-in wide. A carbon steel collimator assembly is located just outboard of the beam tube window. This collimator assembly provides further neutron-beam collimation and houses a fast-neutron filter to increase the signal-to-noise ratio at the neutron scattering instruments.