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College Park, Maryland      June 6 - 10 , 2004

MP17: A Resonance Detector Technique optimized for inelastic neutron scattering studies at the eV energies in condensed matter

C. Andreani (Università degli Studi di Roma “Tor Vergata”, Physics Department, Via della Ricerca Scientifica 1,00133 Italy; Istituto Nazionale per la Fisica della Materia), G. Gorini, E. Perelli-Cippo (Università degli Studi di Milano-Bicocca, Dipartimento di Fisica; Istituto Nazionale per la Fisica della Materia), A. Pietropaolo (Istituto Nazionale per la Fisica della Materia; Università degli Studi di Roma “Tor Vergata”, Physics Department, Via della Ricerca Scientifica 1,00133 Italy), M. Tardocchi (Istituto Nazionale per la Fisica della Materia; Università degli Studi di Milano-Bicocca, Dipartimento di Fisica), E. M. Schooneveld (ISIS, Rutherford Appleton Laboratory), R. Senesi (Istituto Nazionale per la Fisica della Materia; Università degli Studi di Roma “Tor Vergata”, Physics Department, Via della Ricerca Scientifica 1,00133 Italy), N. Rhodes (ISIS, Rutherford Appleton Laboratory)

The talk will address a novel experimental neutron scattering technique (Resonance Detector Technique-RDT) suited for the study of high energy excitations in condensed matter. The technique is intended for neutron scattering experiments at very low angle scattering angle (1° < 2&θ < 5°) on an inverse geometry instrument. It allows to perform High energy Inelastic Neutron Scattering (HINS) experiments in an extended (kinematical unlimited) energies transfer, i.e.ω < 300 meV, coupled to low momentum transfer, i.e. in range 3 Å-1 < q < 10 Å-1. The RDT exploits a novel concepts for the detection of scattered neutrons at the eV energies, i.e. resonance radiative neutron capture for energy analysis. The detection system consists of scintillator detectors which are used to reveal the prompt γ radiation cascade emitted by an absorbing foil after resonance capture. The analyser foil is used as monochromator, to fix energy of neutron after scattering with the sample. The RDT principles will be revisited as compared to RFT (Resonance Foil Technique).

Systematic experimental work performed on VESUVIO in RDT configuration using NaI(Tl) and YAP scintillators as well as CZTe solid state detectors, will be presented. The all set of detector devices were used coupled to a 238U analyser foils and experiments from a standard Pb samples and results compared to that measured in the standard RFS configuration.

Results from a series of HINS experiments, off ice and water, performed on the VESUVIO spectrometer operating at the ISIS pulsed neutron source, will be discussed. The instrument was specifically sets up in the Resonance Detector Spectrometer (RDS) configuration. These results well compared with previous best available results on the same system obtained through an Inelastic Neutron Scattering on a direct geometry instrument. In the case of ice the hydrogen projected density of states has been successfully derived. In water experimental results include the mean kinetic energy in water. As in previous example on ice, a satisfactory agreement is found with values of <Ek> available from previous experiments.

Future development of this technique will be discussed, new areas of experimental research envisaged. These include energy excitations in condensed matter systems: dispersion relations of high energy excitations in metals, semiconductors and insulators, high lying molecular rotational-vibrational states, molecular electronic excitations and electronic level in solids.

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