The development of the BRISP spectrometer at the Institut Laue-Langevin

Inelastic neutron scattering experiments for advanced investigations of the atomic and spin dynamics of matter at low momentum transfers (Neutron Brillouin Spectroscopy) require new instrumentation and efficient measuring techniques. In this paper we describe the development and expected performance of the BRISP thermal neutron spectrometer, which is going to be commissioned by the end of this year at the High-Flux Reactor of the Institut Laue-Langevin in Grenoble. This instrument is specially designed for small-angle spectroscopy at thermal neutron energies with good energy and wavevector transfer resolution. The use of the time-of-flight technique in combination with a two-dimensional position sensitive detector, which ensures an efficient data collection, makes this new spectrometer particularly suited for measuring changes in the dynamic structure factor induced by varying external parameters such as pressure, temperature and magnetic field. A detailed technical discussion, describing the operational characteristics and the potential of BRISP, is presented.