* Corresponding author. Tel.: #39-6-72594549; fax: #39-6- 2023507. E-mail address: senesi@roma2.infn.it (R. Senesi) Physica B 276}278 (2000) 200}201 VESUVIO: a novel instrument for performing spectroscopic studies in condensed matter with eV neutrons at the ISIS facility R. Senesi*, C. Andreani, Z. Bowden, D. Colognesi, E. Degiorgi, A.L. Fielding, J. Mayers, M. Nardone, J. Norris, M. Praitano, N.J. Rhodes, W.G. Stirling, J. Tomkinson, C. Uden INFM-UdR di Roma Tor Vergata, Via della Ricerca Scientixca 1, 00133 Roma, Italy Dipartimento di Fisica, Universita % degli Studi di Roma **Tor Vergata++ and INFM-UdR di Roma Tor Vergata, Via della Ricerca Scientixca 1, 00133 Roma, Italy ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX UK CNR, Viale dell'Universita % 11, 00145 Roma (IT) and INFM-UdR di Roma Tor Vergata, Via della Ricerca Scientixca 1, 00133, Italy Department of Physics, Oliver Lodge Laboratory, University of Liverpool, L69 7ZE UK Dipartimento di Fisica **E. Amaldi++, Universita % degli Studi di Roma Tre and INFM-UdR di Roma Tre, Via della Vasca Navale 84, 00146 Roma, Italy R.M.P., V.le E.Ortolani 194, 00125 Dragona, Italy Abstract The VESUVIO project aims to provide unique prototype instrumentation at the ISIS-pulsed neutron source and to establish a routine experimental and theoretical program in neutron scattering spectroscopy at eV energies. This instrumentation will be speci"cally designed for high momentum, (20 A s (q(150 A s ), and energy transfer ('1 eV) inelastic neutron scattering studies of microscopic dynamical processes in materials and will represent a unique facility for EU researchers. It will allow to derive single-particle kinetic energies and single-particle momentum distributions, n(p), providing additional and/or complementary information to other neutron inelastic spectroscopic techniques.  2000 Elsevier Science B.V. All rights reserved. Keywords: Neutron instruments; Momentum distribution; Incoherent scattering Inelastic neutron scattering at high-momentum trans- fer can provide direct information on the atomic momentum distribution, n(p), when the impulse approxi- mation (IA) is valid. The latter is only reached in recoil scattering when the energy and momentum transfer are su$ciently large by utilising large incident neutron ener- gies generally in excess of 1 eV, such as those typically available on spallation neutron sources. The technique known as deep inelastic neutron scattering (DINS) relies upon the fact that in the IA framework the scattering is no longer a function of the energy and momentum trans- fer separately and the  and q variables can be coupled through the West variable [1}3], y, de"ned by y"M/q(!(q/2M)), where M is the mass of the target atom. The scattering law can thus be written, in the case of isotropic systems J(y)"q/MS(q,)"2    pn(p)dp, (1) where S(q,) is the usual inelastic structure factor. The measurement of J(y) thus allows to derive single-particle 0921-4526/00/$ - see front matter  2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 9 9 ) 0 1 2 4 6 - 6