The TRIUMF Thermal Neutron Facility

The beam stop for the 500 MeV, 100 ¿A beam from the TRIUMF cyclotron has been optimized to provide a variety of facilities for fundamental and applied research. These include: facilities for irradiating specimens with high-energy protons for research and for isotope production; facilities for irradiating specimens with neutrons of all energies from thermal to 500 MeV; and collimated neutron beams from the assembly core, primarily of thermal energies but also of epithermal and higher energies. The combination of these facilities in one unit has resulted in a compact design with substantial savings in shielding and space. The unit consists of a molten lead stopping target surrounded by an H2O/D2O moderator, an H2O reflector and iron and concrete shielding. Most of the beam power (50 kW) is transferred by natural convection in the molten lead to the target wall. From there it is transferred by nucleate boiling to the surrounding H2O moderator. Subsequently the heat is transferred by natural convection to a heat exchanger coil in the upper half of the moderator tank. The facility was commissioned early in 1978. This paper discusses design details, operational experience and measured neutron fluxes and activation levels.