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

Lin, J. Y. Y. and Aczel, A. A. and Abernathy, D. L. and Nagler, S. E. and Buyers, W. J. L. and Granroth, G. E. (2014) Using Monte Carlo ray tracing simulations to model the quantum harmonic oscillator modes observed in uranium nitride. Physical Review B, 89 (14). Art. No. 144302. ISSN 1098-0121.

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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., Nat. Commun. 3, 1124 (2012)]. These modes are well described by three-dimensional 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 nitrogen QHO scattering, contributions that arise from the acoustic portion of the partial phonon density of states, 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.

Item Type:Article
Related URLs:
URLURL TypeDescription DOIArticle
Lin, J. Y. Y.0000-0001-9233-0100
Abernathy, D. L.0000-0002-3533-003X
Granroth, G. E.0000-0002-7583-8778
Additional Information:© 2014 American Physical Society. Received 13 March 2014; published 7 April 2014. This research was supported by the U.S. Department of Energy, Office of Basic Energy Sciences. A.A.A., D.L.A., G.E.G., and S.E.N. were fully supported and J.Y.Y.L. was partially supported by the Scientific User Facilities Division. Neutron scattering experiments were performed at the Spallation Neutron Source, which is sponsored by the Scientific User Facilities Division. We thank B. Fultz, M. E. Hagen, A. I. Kolesnikov, A. J. Ramirez-Cuesta, G. D. Samolyuk, and G. M. Stocks for stimulating discussions. We also thank M. Reuter and S. Campbell for updating the MANTID code to read in the Monte Carlo generated data.
Funding AgencyGrant Number
Department of Energy (DOE)UNSPECIFIED
Issue or Number:14
Classification Code:PACS: 61.05.F-, 63.20.dd
Record Number:CaltechAUTHORS:20140519-100601105
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:45817
Deposited By: Tony Diaz
Deposited On:20 May 2014 03:07
Last Modified:09 Mar 2020 13:18

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