Monte Carlo tool for neutron optics and neutron scattering instrument design

Unlike x-ray generators, neutron sources have inherently low bri ghtness, and care must be exerted in the design of neutron scattering instruments and their coupling to the source to ensure optimal use of the beam. We present a general, versatile Monte Carlo tool for the computer simulation of neutron optics and neutro n scattering instruments that allows a user to produce computer models of an instrument and study its performance quantitatively. The Neutron Instrument Simulation Package (NISP) implements a wide range of neutron optics models to describe neutron transpo rt (including gravity) and scattering in the elements making up the instrument. The program is freely available on the world -wide web at http://strider.lansce.lanl.gov/NISP/Welcome.html