MC simulations of reflectometers at reactor and spallation sources

Abstract

We simulated spectra of reflectometers installed on pulsed sources as they are planned for the ESS (5 MW, 50 Hz short pulse, 1 MW, 10 Hz short pulse, and 5 MW, 16.67 Hz long pulse); for each of the sources a coupled moderator was used. For comparison of spallation and reactor sources, we simulated an instrument with equivalent parameters installed on a reactor source with a neutron flux of the ILL. For comparability of the data, constant wavelength and angular resolutions (of 3% and 8% were used for all instruments. The intensity at the detector was determined as a function of the momentum transfer for a virtual sample of total reflectivity and for deuterated water. Finally, it was calculated how long it takes for each source to measure the entire spectrum with a given statistical accuracy. Best results were obtained at the 50 Hz short-pulse source and the long-pulse source, while the 10 Hz short-pulse source performed worse. The measuring time calculated for the reactor source was the longest.