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Title: Using Monte Carlo ray tracing simulations to model the quantum harmonic oscillator modes observed in uranium nitride

Recently an extended series of equally spaced vibrational modes was observed in uranium nitride (UN) by performing neutron spectroscopy measurements using the ARCS and SEQUOIA time-of- flight chopper spectrometers [A.A. Aczel et al, Nature Communications 3, 1124 (2012)]. These modes are well described by 3D isotropic quantum harmonic oscillator (QHO) behavior of the nitrogen atoms, but there are additional contributions to the scattering that complicate the measured response. In an effort to better characterize the observed neutron scattering spectrum of UN, we have performed Monte Carlo ray tracing simulations of the ARCS and SEQUOIA experiments with various sample kernels, accounting for the nitrogen QHO scattering, contributions that arise from the acoustic portion of the partial phonon density of states (PDOS), and multiple scattering. These simulations demonstrate that the U and N motions can be treated independently, and show that multiple scattering contributes an approximate Q-independent background to the spectrum at the oscillator mode positions. Temperature dependent studies of the lowest few oscillator modes have also been made with SEQUOIA, and our simulations indicate that the T-dependence of the scattering from these modes is strongly influenced by the uranium lattice.
 [1] ;  [2] ;  [2] ;  [2] ;  [3] ;  [2]
  1. California Institute of Technology, Pasadena
  2. ORNL
  3. National Research Council of Canada
Publication Date:
OSTI Identifier:
DOE Contract Number:
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review B; Journal Volume: 89; Journal Issue: 14
Research Org:
Oak Ridge National Laboratory (ORNL); Spallation Neutron Source
Sponsoring Org:
SC USDOE - Office of Science (SC)
Country of Publication:
United States