Reflectometry at continuous wave and pulsed-neutron sources

Monte Carlo simulations of identical reflectometers viewing a continuous wave (CW) neutron source and a variety of pulsed-neutron sources were undertaken in order to quantify the performance of reflectometers that use either time-of-flight (TOF) or crystal-monochromator techniques to determine neutron wavelength. The performance of a reflectometer includes its capability to produce accurate information, and the speed in which the information is gathered. We find: (1) Properly calibrated reflectometers at any neutron source can produce equally accurate and precise data. (2) Reflectometers at pulsed-sources are always faster than a reflectometer using a monochromator at a CW source of equal time-average flux. (3) Reflectometers viewing low-frequency sources performed faster than those viewing higher frequency sources of equal power, provided the measurement of a large region of reciprocal space was required. (4) Reflectometers at short-pulsed-sources performed marginally better than those at long-pulsed-sources of equal power, frequency and instrumental resolution. The primary design criterion for a pulsed-source to be optimized for reflectometry studies is to maximize moderator brightness per pulse. A criterion of secondary importance is the reduction of the source frequency.