Thermal neutron leakage and time structure measured for various target-moderator-reflector configurations for a spallation neutron source

Measurements were performed at the Swiss Institute of Nuclear Research of the integrated thermal neutron leakage, the thermal neutron flux distribution and the time structure of the thermal neutron field for various configurations of target, moderator and reflector for a spallation neutron source. Among them were a cylindrical Pb-Bi-target in a D20-tank and a slab target with a hybrid moderator configuration consisting of a D20 half tank below and a reflected H20 moderator above the target. The results are used to predict performance data for a spallation neutron source with 500 μs long proton pulses. Although there remains some ambiguity due to non-perfect simulation of the real situation, correction factors derived from independent measurements could be used. The effect of beam tubes in the D20 on the thermal neutron flux was measured directly. (orig.)