In the Target Station, fast, high-energy neutrons are released by spallation from the target consisting of neutron-rich material, a heavy metal called tungsten, when a high-energy beam of protons from the accelerator impinges on it. The neutrons, which are travelling at 10 per cent of the speed of light, are then slowed down to roughly the speed of sound, using moderators and reflectors, to provide intense pulses of neutrons at velocities and energies that are useful for experiments. Once moderated, the neutrons are delivered to the instruments through beam ports radiating from the Target Station.
Key features of the Target Station are the target itself, the neutron moderator, pre-moderator and reflector system, the beam-extraction system and shielding. The Target Station must also incorporate a powerful helium-based cooling system able to dissipate the heat generated by the powerful 5 MW proton beam hitting the target. Radioactive isotopes and radiation is generated by the spallation process and by general activation of components. The target will therefore be surrounded by steel shielding in the form of the cylindrical, 6,000-tonne Target Station monolith to prevent unwanted ionising radiation from escaping.