M Krzystyniak

Mass-selective Neutron Spectroscopy Beyond the Proton

We discuss ongoing methodological developments underpinning the determination of nuclear-momentum distributions from mass-resolved neutron Compton data of lightweight materials. To this end, two systems are considered in detail, namely, lithium hydride (including its deuterated counterpart) and squaric acid, an organic antiferroelectric material containing hydrogen, carbon, and oxygen. Beyond the usual case of the proton, our approach enables direct access to detailed line shape information associated with the underlying nuclear-momentum distributions of both deuterium and lithium. For oxygen and carbon, mean kinetic energies can also be obtained directly from the neutron data, as demonstrated by a detailed analysis of mass- resolved data from squaric acid. From an instrumentation point of view, this work provides a suitable platform for a detailed assessment of existing capabilities and future developments in mass-selective neutron spectroscopy on the VESUVIO spectrometer at ISIS.

The VESUVIO Spectrometer Now and When

The current layout and mechanics of the VESUVIO spectrometer are presented in light of spectroscopic measurements using electron-volt neutrons. A brief background to the theoretical framework of deep inelastic neutron scattering is presented, with focus on data collection and instrumental design. The current capabilities and research themes for VESUVIO are discussed, and possible future instrumental developments highlighted which will enhance the instruments ability to meet scientific inquiry and expectation.

VESUVIO Data Analysis Goes MANTID

This paper describes ongoing efforts to implement the reduction and analysis of neutron Compton scattering data within the MANTID framework. Recently, extensive work has been carried out to integrate the bespoke data reduction and analysis routines written for VESUVIO with the MANTID framework. While the programs described in this document are designed to replicate the functionality of the Fortran and Genie routines already in use, most of them have been written from scratch and are not based on the original code base.

Neutrons Matter – VII International Workshop on Electron-Volt Neutron Spectroscopy

Science is a superb way of transcending national boundaries and political circumstances. The long-standing agreement between the Italian Consiglio Nazionale delle Ricerche (CNR) and the British Sci...

Neutrons matter: VII international workshop on electron-Volt neutron spectroscopy – A preface to the workshop proceedings

We present here a collection of works reporting on the recent experimental and theoretical activities taking advantage of epithermal neutron spectroscopy, and in particular focusing on recent results presented during the VII International Workshop on Electron-Volt Neutron Spectroscopy held in Rome on 7-8 November 2018.

VESUVIO+: The Current Testbed for a Next-generation Epithermal Neutron Spectrometer

We present an overview of ongoing developments in epithermal neutron spectroscopy using the VESUVIO+ beam line at the ISIS Facility. In its current incarnation, VESUVIO+ provides a suitable platform for further and much-needed progress in the judicious exploitation of epithermal neutrons at a pulsed spallation source, as well as constitutes a necessary milestone towards a next-generation station for Epithermal and Thermal Neutron Analysis, hereafter ETNA. In particular, we discuss recent improvements in capability relative to its predecessor VESUVIO. These include the concurrent use of mass-resolved neutron spectroscopy, transmission, and diffraction to explore the properties of complex functional materials, as well as the implementation of techniques unique to pulsed neutron sources such as γ-ray dopplerimetry and energy-resolved prompt-γ activation analysis.

Atomic Quantum Dynamics in Materials Research

The motion of atoms in materials is generally treated within the classical framework of Newtons laws and molecular dynamics. In this limit, atoms move with mean kinetic energy proportional to the temperature of the system, as in the case of a perfect gas of noninteracting particles. For systems with more quantized degrees of freedom, such as intramolecular motions, or in the descriptions of the influence of a finite kinetic energy of the atoms on the properties of solids, atomic dynamics may be described in terms of a normal-mode, harmonic oscillator picture, or treated with rigid constraints. However, there are a number of important examples where atoms should be treated as fully quantum objects, with their dynamics derived from a Schrodinger equation based on a well-defined interatomic interaction potential. Such an approach is mandatory in order to describe nuclear quantum effects, such as zero-point energies. The quantum nature of atoms can be quantitatively described by nuclear momentum distributions and mean kinetic energies of atoms. These observables are accessible using deep inelastic neutron scattering, a technique based on the use of epithermal neutrons available at instruments at spallation neutron sources. VESUVIO is the most successful example of this type of instrument and it is based at the ISIS Facility, UK. A description of deep inelastic neutron scattering and the VESUVIO spectrometer is presented here, together with the conceptual framework and a number of case studies to emphasize the role of nuclear quantum effects in condensed matter systems.

Discussion: Theoretical Horizons and Calculation

Reference EPFL-CONF-205200doi:10.1088/1742-6596/571/1/012013View record in Web of Science Record created on 2015-02-20, modified on 2017-12-10

Proton momentum distribution and anomalous scattering intensities in a pseudo-spherical ammonium ion: a neutron Compton scattering study of (NH4)2PdCl6 and (NH4)2TeCl6

Neutron Compton scattering (NCS) measurements on ammonium hexachloropalladate and hexachlorotellurate were performed at room temperature. Proton scattering intensities and momentum distributions, as measured in the NCS experiment, have been compared with results expected from the impulse approximation (IA) for both systems. The measurement shows that scattering intensity from protons is anomalous even though their momentum distribution has a second moment that agrees very well with the ab initio calculation for an isolated pseudo-spherical NH(4)(+) ion in the ground vibrational state. Detailed data analysis shows that there is no extra (beyond the IA expected value) broadening or peak shift of proton momentum distribution due to ultra-fast kinetics of the Compton scattering process leading to anomalous scattering intensities. This is most probably due to highly symmetric local potential in the NH(4)(+). Presented results have interesting implications for further theoretical work in the field.