@article{hawari_gillete_2014, title={Inelastic Thermal Neutron Scattering Cross Sections for Reactor-grade Graphite}, volume={118}, ISSN={["1095-9904"]}, DOI={10.1016/j.nds.2014.04.030}, abstractNote={Current calculations of the inelastic thermal neutron scattering cross sections of graphite are based on representing the material using ideal single crystal models. However, the density of reactor-grade graphite is usually in the range of 1.5 g/cm3 to approximately 1.8 g/cm3, while ideal graphite is characterized by a density of nearly 2.25 g/cm3. This difference in density is manifested as a significant fraction of porosity in the structure of reactor-grade graphite. To account for the porosity effect on the cross sections, classical molecular dynamics (MD) techniques were employed to simulate graphite structures with porosity concentrations of 10% and 30%, which are taken to be representative of reactor-grade graphite. The phonon density of states for the porous systems were generated as the power spectrum of the MD velocity autocorrelation functions. The analysis revealed that for porous graphite the phonon density of states exhibit a rise in the lower frequency region that is relevant to neutron thermalization. Using the generated phonon density of states, the inelastic thermal neutron scattering cross sections were calculated using the NJOY code system. While marked discrepancies exist between measurements and calculations based on ideal graphite models, favorable agreement is found between the calculations based on the porous graphite models and measured data.}, journal={NUCLEAR DATA SHEETS}, author={Hawari, A. I. and Gillete, V. H.}, year={2014}, month={Apr}, pages={176–178} }
 @article{bennun_mayer_korochinsky_gillette_2009, title={Uranium assay in mineral samples by means of neutron detection of uranium-238 spontaneous fission}, volume={267}, ISSN={["0168-583X"]}, DOI={10.1016/j.nimb.2008.11.054}, abstractNote={Abstract An “in situ” method to determine uranium content in mineral samples by means of detecting neutrons from 238 U spontaneous fission is presented. The method is simple, exact, reliable and passive (it does not need any external excitation source). The technique was experimentally validated, and those experiments were also modeled by a Monte Carlo neutron transport code (MCNP), to check the concordance between experimental results and simulations. Relying on this concordance, calculation ability to describe hypothetical situations was established. The influence of many factors (multiplicative medium, electronic noise, etc.) was estimated. The results obtained allow us to affirm that, with this method it is possible to determine concentrations of 0.05 wt% of uranium (detection limit). The technique has the advantage of sampling very considerable mineral volumes (≈0.2 m 3 ).}, number={3}, journal={NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS}, author={Bennun, Leonardo and Mayer, Roberto and Korochinsky, Sergio and Gillette, Victor}, year={2009}, month={Feb}, pages={525–534} }
 @article{hehr_hawari_gillette_2007, title={Molecular dynamics simulations of graphite at high temperatures}, volume={160}, ISSN={["1943-7471"]}, DOI={10.13182/NT07-A3897}, abstractNote={Graphite, a key structural and moderator material in the proposed Generation IV roadmap, is expected to experience irradiation at temperatures up to 1800 K. In this study, a molecular dynamics (MD) code is developed for the purpose of performing atomistic simulations of high-temperature graphite. The MD computations are benchmarked against thermal expansion and mean-squared displacement data, and modifications to the potential energy function are devised as needed to fit experimental measurements. Graphite-specific alterations include a plane-by-plane center-of-mass velocity correction, anisotropy in the potential energy cutoff function, and temperature-dependent parameterization of the interatomic potential. The refined MD model is then employed to investigate the threshold displacement energy at temperatures of 300 and 1800 K. It was found that the threshold displacement energy depends strongly on the knock-on direction, yet the angle-averaged threshold energy exhibits relatively little variation with temperature.}, number={2}, journal={NUCLEAR TECHNOLOGY}, author={Hehr, Brian D. and Hawari, Ayman I. and Gillette, Victor H.}, year={2007}, month={Nov}, pages={251–256} }
 @article{mishra_hawari_gillette_2006, title={Design and performance of a thermal neutron imaging facility at the North Carolina State University PULSTAR reactor}, volume={53}, ISSN={["1558-1578"]}, DOI={10.1109/tns.2006.884323}, abstractNote={A thermal neutron imaging facility has been set up at the North Carolina State University PULSTAR reactor. The PULSTAR is an open pool light water moderated 1 MWth research reactor with six beam tubes. The present facility is set up on beam tube # 5 of the reactor. The facility is intended to have radiographic and tomographic capabilities. The design of the neutron collimator was performed using MCNP5. The collimator includes a 4-in bismuth filter followed by a 6-in single-crystal sapphire filter. Thermal neutron scattering cross-section libraries for sapphire and bismuth were generated and used in the MCNP simulation of the system. Based on the current design, the L/D of the facility ranges between 100 and 150. The neutron flux at the image plane can be varied from 1.8times106 to 7times106 n/cm2middots with a Cd-ratio of ~450. The resolution of the system for different imaging media was also estimated and found to be ~33 mum for conventional radiography film and ~110 mum for digital image plates. Initial measurements, using ASTM standards, show that the imaging facility achieves a beam quality classification of IA}, number={6}, journal={IEEE TRANSACTIONS ON NUCLEAR SCIENCE}, author={Mishra, Kaushal K. and Hawari, Ayman I. and Gillette, Victor H.}, year={2006}, month={Dec}, pages={3904–3911} }