Light atom quantum oscillations in UC and US

Abstract

High-energy vibrational scattering in the binary systems UC and US is measured using time-of-flight inelastic neutron scattering. A clear set of well-defined peaks equally separated in energy is observed in UC, corresponding to harmonic oscillations of the light C atoms in a cage of heavy U atoms. The scattering is much weaker in US and only a few oscillator peaks are visible. We show how the difference between the materials can be understood by considering the neutron scattering lengths and masses of the lighter atoms. Monte Carlo ray tracing is used to simulate the scattering, with near quantitative agreement with the data in UC, and some differences with US. The possibility of observing anharmonicity and anisotropy in the potentials of the light atoms is investigated in UC. Overall, the observed data is well accounted for by considering each light atom as a single atom isotropic quantum harmonic oscillator.

Recent developments of MCViNE and its applications at SNS

“…Its capability of simulating multiple scattering was demonstrated in a study of ARCS and SEQUOIA experiments measuring a uranium nitride sample [5], in which multiple scattering simulation reproduced well the extra intensities in low Q region of measured spectra for high order quantum harmonic oscillation excitations. Further studies on uranium carbide (UC) and uranium sulfide (US) show that intensity variation can be captured by MCViNE simulations as the scattering cross section varies with elements (nitrogen/ carbon/sulfur) [23]. However some disagreement is seen in the US study where the background scattering is comparable, or larger, than the scattering from sulfur, which has smaller scattering cross section than aluminum, the material of the sample holder.…”

Momentum and energy dependent resolution function of the ARCS neutron chopper spectrometer at high momentum transfer: Comparing simulation and experiment

“…The MCViNE software package [29] is an object oriented (OO) Monte Carlo neutron ray tracing package for modeling and simulation of neutron scattering experiments on modern neutron spectrometers as described in detail in Refs. [28,30,16]. MCViNE simulations were performed in four steps to reproduce the experiments in high fidelity:…”

“…[ 28,30,16]. MCViNE simulations were performed in four steps to reproduce the experiments in high fidelity:…”

“…1. Beam simulation: The incident beam on the sample was simulated using the same benchmarked instrument model used in previous research [28,30,16].…”

Simulating and benchmarking neutron total scattering instrumentation from inception of events to reduced and fitted data

“…Ray-tracing simulations have been used to evaluate instrumental resolution functions (Vickery et al, 2013;Š aroun & Kulda, 1997Š aroun & Kulda, , 2008 for inelastic neutron spectrometers like VESPA (Fedrigo et al, 2016), SEQUOIA (Granroth & Hahn, 2015) and 4SEASONS (Kajimoto et al, 2018) to name a few. Recently, extension of ray-tracing simulations to particular samples has been used to distinguish between sample physics and subtleties including instrument resolution (Leiner et al, 2019;Hahn et al, 2014) and multiple scattering (Lin et al, 2014;Yiu et al, 2016), for example. Similarly, Monte Carlo ray-tracing studies have been performed to evaluate the instrument design and resolution of TOF powder diffractometers (Lieutenant et al, 2006;Schweika et al, 2016;Š aroun & Beran, 2014) and smallangle scattering instruments (Lieutenant et al, 2005 (Laliena et al, 2020).…”