Studies of a lead reflector for a pulsed neutron source

This paper examines the consequences of adopting a non-moderating reflector and compares its performance to that of beryllium. Reflector studies on a time modulated source have shown lead to be an excellent reflector, maintaining the structure of the long time pulse (500 μs) marginally better than beryllium and with a slightly superior yield. Engineering, fabrication and cost factors as well as improved gamma and fast neutron shielding properties further favour lead as a reflector for these sources. Even for truly pulsed sources which rely primarily on time of flight for energy selection, Monte Carlo studies have shown that a lead reflector maintains an excellent time structure in hydrogenous moderators in the slowing down region. This paper describes the experimental comparison of lead and beryllium reflectors for the case of a pulsed spallation source. The target-moderator-reflector configuration used was a mock-up of the Rutherford Appleton Laboratory's SNS geometry. The experiments were performed in the low current target area of the Los Alamos National Laboratory's spallation source, the WNR. This work was complemented by Monte Carlo calculations using the TIMOC code