Double difference method in deep inelastic neutron scattering on the VESUVIO spectrometer

Abstract

The principles of the Double Difference (DD) method, applied to the neutron spectrometer VESUVIO, are discussed. VESUVIO, an inverse geometry spectrometer operating at the ISIS pulsed neutron source in the eV energy region, has been specifically designed to measure the single particle dynamical properties in condensed matter. The width of the nuclear resonance of the absorbing filter, used for the neutron energy analysis, provides the most important contribution to the energy resolution of the inverse geometry instruments. In this paper, the DD method, which is based on a linear combination of two measurements recorded with filter foils of the same resonance material but of different thickness, is shown to improve significantly the instrumental energy resolution, as compared with the Single Difference (SD) method. The asymptotic response functions, derived through Monte-Carlo simulations for polycrystalline Pb and ZrH 2 samples, are analysed in both DD and SD methods, and compared with the experimental ones for Pb sample. The response functions have been modelled for two distinct experimental configurations of the VESUVIO spectrometer, employing 6 Li-glass neutron detectors and NaI g detectors revealing the g-ray cascade from the ðn; gÞ reaction, respectively. The DD method appears to be an effective experimental procedure for Deep Inelastic Neutron Scattering measurements on VESUVIO spectrometer, since it reduces the experimental resolution of the instrument in both 6 Li-glass neutron detector and g detector configurations.

Foil cycling technique for the VESUVIO spectrometer operating in the resonance detector configuration

“…The acquired signal is a TOF spectrum where the count rate per time bin is given, with good degree of accuracy, by the approximated expression 11,27 …”

“…This analyzer component of the resolution function ͑referred to as the energy component͒ has to be convoluted with the other ͑geometrical and time͒ components of the spectrometer resolution ͑which can be well approximated by a Gaussian͒, thus resulting in a Voigt line shape for the overall resolution function. 11,31,32 …”

“…Several studies have been performed in the last six years on VESUVIO, optimizing different combinations of analyzers and photon detectors 11,[14][15][16][17][18][19] in the RD configuration. These studies have demonstrated that cerium activated yttrium-aluminum-perovskite ͑YAP͒ scintillators are the most promising detectors in terms of efficiency and signal to background ratio enhancement.…”

Excess of Proton Mean Kinetic Energy in Supercooled Water

“…Upon sample crystallization, data collected during the previous two hours were discarded; subsequently the sample was heated to 300 K, and then cooled down. Data have been acquired employing the single difference (SD) and the double difference (DD) methods [17], the latter providing a narrower instrumental resolution (see Fig. 1).…”

Proton Momentum Distribution in a Protein Hydration Shell

“…Measurements were made at 180 and 290 K, above and below the crossover temperature T c . Experimental data at both temperatures have been acquired in the standard resonance filter configuration, employing the single difference (SD) and the double difference (DD) methods [19], the latter providing a narrow instrumental resolution, with the aim of carrying out a detailed line shape analysis of the proton NCP. Standard data reduction procedures have been applied to obtain the fixed-angle experimental NCP, F y; J y; R y; [17,20], R y; being the fixed-angle spectrometer resolution.…”