Optimisation of a thermal neutron guide by Monte Carlo simulations

The single-crystal diffractometer REciprocal Space Investigator (RESI) will be installed on thermal beamline SR8 at the new neutron source FRM-II in G arching. The remote location of the instrument in the reactor hall will pro vide low background but also requires the use of a neutron guide. In order to optimise the neutron guide regarding intensity, profiles, divergences an d wavelength resolution at monochromator and sample positions comprehensive Monte Carlo simulations were carried out. Finally, a straight but focusing guide performed best. The simulation results for different guide geometrie s are discussed. (C) 2000 Elsevier Science B.V. All rights reserved.