The Brillouin spectrometer BRISP at the ILL

In recent years several experiments carried out by means of inelastic X-ray and neutron scattering on liquid and amorphous systems have shown that collective modes exist in the low-momentum region well beyond the hydrodynamic limit. To expand the potentialities of the neutron technique in this field, a small-angle inelastic spectrometer operated at thermal neutron energies has been designed, built and installed at the high-flux reactor of the Institut Laue Langevin in Grenoble (France). The instrument is designed to take advantage of the high neutron flux available at the thermal source of the reactor thus enabling experiments at incoming neutron energies from 20 up to 120 meV and scattering angles as low as 0.5^∘. A hybrid configuration which couples a crystal monochromator and a time of flight final energy analysis is exploited. Preliminary tests obtained with the large-area (≃1.5 m²) position-sensitive detector are presented.