Abstract
New evidence of the increased count rate in deep inelastic neutron scattering spectra is provided. Experiments were performed using photon-sensitive yttrium-aluminum-perovskite detectors, installed on the VESUVIO spectrometer at the ISIS pulsed neutron and muon source. At present, these detectors work with a low-level discrimination threshold measuring photons with energy greater than 600 keV in order to avoid background photons from the boron in the beam stop, and other environmental sources. We discuss the advantage in reducing the level of the threshold so as to detect some high-intensity low-energy promptgamma rays emitted after the radiative capture of 4.9 eV neutrons by gold, used as energy analyser on the VESUVIO spectrometer. This work shows an improvement of the statistical poissonian error bars and noise on the difference of spectra recorded with and without the energy analyser. The application of such new acquisition strategy discussed here will improve the detection limit of hydrogen atoms in samples, as well as allow a more precise line-shape analysis of nuclear momentum distributions, mentioning just few applications of deep inelastic neutron scattering experiments on VESUVIO.
Highlights
The quantitative and non-destructive assessment of hydrogen content in bulk samples is a topic of increasing interest in materials science [1, 2, 3]
For high values of energy and momentum transfer, the spectral response of a system is composed of a massresolved collection of peaks which are related to the nuclear momentum distributions of every element in the system [4, 5, 6], with the hydrogen peak being the most intense and the best resolved signal
It is evident that lowering the threshold there is a count rate increase, in particular there is about a factor 3 at the hydrogen peak position
Summary
The quantitative and non-destructive assessment of hydrogen content in bulk samples is a topic of increasing interest in materials science [1, 2, 3]. The development of pulsed accelerator-driven neutron facilities provided an optimal framework for the development of eV neutron spectroscopy, owing to a substantial epithermal flux as opposed to research reactors. In such cases, inverted- (direct-) geometry instruments select the final (initial) energy of neutrons using an energy analyser, while the initial (final) energy and the energy transfer are calculated using the Time-Of-Flight (TOF) technique. The detection difficulties are overcome by using foils with narrow and intense nuclear resonances by which a neutron with a certain energy is captured and a prompt-gamma ray cascade is emitted and efficiently recorded by gammasensitive detectors. Several materials have been discussed in pioneering experiments at the Los Alamos National Laboratory, such as plutonium, rhenium, uranium and gold [10]
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