@article{lee_fleming_hawari_2023, title={Benchmark of Neutron Thermalization in Graphite Using a Pulsed Slowing-Down-Time Experiment}, ISSN={["1943-748X"]}, DOI={10.1080/00295639.2022.2162789}, abstractNote={Abstract A benchmark has been developed using a pulsed slowing-down-time experiment to isolate the thermalization process in graphite. The experiment was conducted at the Oak Ridge Electron Linear Accelerator facility at Oak Ridge National Laboratory, and it measured the time spectrum of neutrons leaking from a graphite pile during slowing down and thermalization within graphite. Simulations of the benchmark experiment were performed using the MCNP6.1 Monte Carlo code and the ENDF/B-VII.1 and ENDF/B-VIII.0 cross-section databases. The benchmark provides a time spectrum (i.e., time-dependent counts in a detector) that allows for validation of the graphite thermal scattering libraries (TSLs). The impact on the simulations using a suite of graphite TSLs was compared with the experimental results. Given the density of nuclear graphite, the TSL corresponding to graphite with 30% porosity, as implemented in ENDF/B-VIII.0, was found to most accurately represent the measured time spectrum corresponding to the thermal energy range with an average deviation of ±1.7%.}, journal={NUCLEAR SCIENCE AND ENGINEERING}, author={Lee, Eunji and Fleming, N. Colby and Hawari, Ayman I.}, year={2023}, month={Feb} }
 @article{ahmed_fleming_hawari_2023, title={Effects of Hydrogen Bonding on Nuclear Data Development of Liquid Anhydrous HF}, volume={284}, ISBN={["*****************"]}, ISSN={["2100-014X"]}, DOI={10.1051/epjconf/202328417003}, abstractNote={Anhydrous Hydrogen Fluoride (HF) at high temperatures and pressures is used to process and manufacture nuclear fuel. As HF is often used directly with uranium, correct neutron thermal scattering cross sections are crucial to criticality safety applications. Classical molecular dynamics (CMD) simulation of the flexible HF system was used to create the thermal scattering law (TSL) and cross sections. The initial 2-site model is used in LAMMPS, and it can not capture the H-bond. To correctly represent the H-bond effects, a second, 3-site model was constructed in GROMACS. The 3-site model handled H-bonds by connecting a massless charge to the molecule. Key model parameters were compared to experimental data to verify the approach and models. To get the normalized VACF, the model was compared using hydrogen and fluorine bond length, density, potential energy, and diffusion coefficient. The phonon DOSs for both models were derived from the normalized VACF. DOSs were used to estimate the TSL (S(α,β)) and neutron thermal scattering cross sections for hydrogen in HF. The TSLs were evaluated using the FLASSH code with the Schofield diffusion model. It was observed that the representation of the hydrogen bonding changes the TSL's diffusional contributions. This is represented in the low energy scattering cross section, where intermolecular binding effects shift the cross section.}, journal={15TH INTERNATIONAL CONFERENCE ON NUCLEAR DATA FOR SCIENCE AND TECHNOLOGY, ND2022}, author={Ahmed, Tanvir and Fleming, N. Colby and Hawari, Ayman I.}, year={2023} }
 @article{fleming_manring_laramee_crozier_lee_hawari_2023, title={FLASSH 1.0: Thermal Scattering Law Evaluation and Cross Section Generation}, volume={284}, ISBN={["*****************"]}, ISSN={["2100-014X"]}, DOI={10.1051/epjconf/202328417007}, abstractNote={The Full Law Analysis Scattering System Hub (FLASSH) is an advanced code which evaluates the thermal scattering law (i.e. TSL, S(α,β)) for thermal scattering cross sections and resonance Doppler broadening. The ability to accurately capture these two key cross section features is dependent on accurate, high fidelity TSL evaluations. FLASSH 1.0 provides advanced physics capabilities resulting in an improved, generalized TSL to most accurately represent the lattice dynamics within any material. This improved TSL will allow for consistent analysis in both the thermal and epithermal energy ranges. The features for TSL analysis are packaged within the FLASSH GUI for easy user interface along with data output in many file formats including ENDF File 7 and ACE files.}, journal={15TH INTERNATIONAL CONFERENCE ON NUCLEAR DATA FOR SCIENCE AND TECHNOLOGY, ND2022}, author={Fleming, N. Colby and Manring, Cole A. and Laramee, Benjamin K. and Crozier, Jonathan P. W. and Lee, Eunji and Hawari, Ayman I.}, year={2023} }
 @article{fleming_manring_laramee_crozier_lee_hawari_2023, title={FLASSH 1.0: Thermal Scattering Law Evaluation and Cross-Section Generation for Reactor Physics Applications}, ISSN={["1943-748X"]}, DOI={10.1080/00295639.2023.2194195}, abstractNote={Abstract The Full Law Analysis Scattering System Hub (FLASSH) is a modern, advanced code that evaluates the thermal scattering law (TSL) along with accompanying cross sections. FLASSH features generalized methods that accommodate any material structure. Historical approximations including incoherent and cubic approximations have been removed. Instead, the latest release of FLASSH features advanced physics options including distinct effect corrections (one-phonon contributions) and noncubic formulations. Noncubic elastic and inelastic contributions are necessary to accurately evaluate one-phonon contributions. Both noncubic and one-phonon calculations require high-density sampling of the various scattering directions. Optimization and parallelization of these routines were therefore necessary to produce results in a reasonable computational time frame. With these notable improvements to the generalized TSL, FLASSH 1.0 can meet benchmark requirements by permitting realistic comparisons with experiments for both TSLs and the resulting integrated cross sections. Within FLASSH, these high-fidelity TSLs can be applied also to the resonance region to evaluate accurate, material structure-dependent Doppler broadening that captures the observed experimental behavior. Additional features including a graphical user interface (GUI), plotting diagnostics, and formatted output options including ACE files allow users to complete a TSL evaluation with minimal input and maximum flexibility. The user GUI creates input files for FLASSH, reducing user error and also providing built-in error checks. Autofill options and suggested input values help make TSL evaluation accessible to novice users. The FLASSH code is compiled to run on both Windows and Linux platforms with automatic parallelization.}, journal={NUCLEAR SCIENCE AND ENGINEERING}, author={Fleming, N. Colby and Manring, Cole A. and Laramee, Briana K. and Crozier, Jonathan P. W. and Lee, Eunji and Hawari, Ayman I.}, year={2023}, month={Apr} }