Speaker
Description
The Full Law Analysis Scattering System Hub (FLASSH) is an advanced code which evaluates the thermal scattering law (i.e. TSL, S($\alpha$,$\beta$)) for thermal scattering cross sections and resonance Doppler broadening. These features in the cross section are both fundamentally driven by target atom vibrations, which are impacted by the nature of the chemical binding and temperature of the lattice. 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. The GUI allows users to visually step through the evaluation process with the added benefit of built-in error checks and automatic input file formatting. The FLASSH GUI also provides automatic default values to inform user inputs as well as tool tips which describe variables and special formatting. After evaluation, the GUI also produces plots which provide quick quality assurance checks for TSL and cross section output. This GUI makes advanced features in FLASSH accessible for users while also reducing the initial learning curve.
The FLASSH code offers traditional means of evaluating the TSL, including liquid diffusional contributions. These traditional codes, however, are limited by the approximations included in their formulations. Historical approximations including the cubic, incoherent, and atom site approximation provide faster results and are computationally less expensive. Previous codes also were hard coded with a limited material selection. FLASSH offers both historical approximated TSL evaluation methods as well as advanced, generalized formulations. All features in FLASSH are generalized to allow for any material to be evaluated. Generalized non-cubic formulations for both the TSL and elastic contributions are available in FLASSH. These non-cubic methods explicitly evaluate the directional dependence of the lattice phonon modes. Additional contributions from the 1-phonon distinct terms adds increased accuracy to the evaluation. With both non-cubic and 1-phonon components, the TSL can then be directly compared with experimental data for benchmarking.
FLASSH produces as output many file formats ranging from formatted user tables to ENDF file 7 and ACE files. Free atom cross sections, particularly the resonance region, can also be treated within FLASSH. Using the TSL evaluation which is published in the ENDF file 7, the process of Doppler broadening can also be performed. To reproduce historical methods, free gas Doppler broadening is also available. The improved physics from FLASSH linking the thermal scattering cross section analysis with the Doppler broadening of resonance cross sections will not only improve the individual components of the evaluations but also will provide a consistent means of analysis for both energy ranges. FLASSH provides superior physics in defining the TSL which will translate into improve Doppler broadening as well as thermal scattering cross sections.