Title: Final Report --- First principles modeling of microscopic scintillation mechanisms

This final report presents work carried out on the project “First Principles Modeling of Mechanisms Underlying Scintillator Non-Proportionality” at Lawrence Livermore National Laboratory during 2013-2015. The scope of the work was to further the physical understanding of the microscopic mechanisms behind scintillator nonproportionality that effectively limits the achievable detector resolution. Thereby, crucial quantitative data for these processes as input to large-scale simulation codes has been provided. In particular, this project was divided into three tasks: (i) Quantum mechanical rates of non-radiative quenching, (ii) The thermodynamics of point defects and dopants, and (iii) Formation and migration of self-trapped polarons. The progressmore » and results of each of these subtasks are detailed.« less

The CRADA participants built on the capabilities LLNL had already developed for ab initio diffusion modeling, extending them to higher doping and damage levels, and applying them to improve the understanding of implant and annealing tradeoffs for technology-relevant conditions. The calculation results and some of the simulation capabilities developed here were transferred to Intel and Applied Materials.

A 56-node Intel Paragon parallel computer was purchased with major support provided by this grant, and installed in July, 1993, in the Center for Scientific Computing, Department of Applied Mathematics and Statistics, SUNY - Stony Brook. The targeted research funded by this proposal consists of work to support the Stony Brook and Brookhaven National Laboratory contributions to the Partnership in Computational Science (PICS) program; namely environmental remediation modeling of ground water transport, Car-Parrinello first principles molecular dynamics calculations, and the supporting development of the parallelized VolVis graphics package. Research accomplishments to date for this targeted research is discussed in {section}2.more » This computer has also enabled or enhanced many other projects conducted both by the Center for Scientific Computing and by the Department of Applied Mathematics and Statistics. These other projects include two- and three-dimensional gas dynamics using front tracking, other molecular dynamics applications, kidney modeling, and global optimization techniques applied to DNA-protein interactions. Technical summaries of these additional projects are presented in {section}3. The targeted research includes users from the Departments of Applied Mathematics and Computer Science at SUNY - Stony Brook, as well as staff scientists from the Departments of Physics and Applied Sciences at Brookhaven National Laboratory. The additional projects involve university faculty from the above departments as well as the Departments of Physics and Chemistry. Regular users of this machine currently include 10 faculty members, 8 postdoctoral fellows, more that 12 PhD students and approximately 8 staff members from BNL.« less

Ab initio Quantum mechanics calculations of the equation of states for BaZrO{sub 3} have been performed and the bulk modulus has been obtained. The value of the modulus is in good agreement with reported experimental values. Equilibrium proton positions in Y-doped BaZrO{sub 3} with dopant concentrations from 12.5 to 50% were investigated. Initial rough estimates of the transition barriers have been made. Our results suggest that the proton migration pathway may involve secondary minima with two maxima (symmetric with respect to the center of the path). In the next phase of this project the results of our quantum mechanical calculationsmore » will be used to develop a new Reactive Force Field (ReaxFF) based on first principles. This Reactive Force Field will be used for much molecular dynamics simulations or much larger systems to investigate proton migration in bulk and surface regions of fuel cells.« less

LIFE fusion is designed to generate 37.5 MJ of energy per shot, at 13.3 Hz, for a total average fusion power of 500 MW. The energy from each shot is partitioned among neutrons ({approx}78%), x-rays ({approx}12%), and ions ({approx}10%). First wall heating is dominated by x-rays and debris because the neutron mean free path is much longer than the wall thickness. Ion implantation in the first wall also causes damage such as blistering if not prevented. To moderate the peak-pulse heating, the LIFE fusion chamber is filled with a gas (such as xenon) to reduce the peak-pulse heat load. Themore » debris ions and majority of the x-rays stop in the gas, which re-radiates this energy over a longer timescale (allowing time for heat conduction to cool the first wall sufficiently to avoid damage). After a shot, because of the x-ray and ion deposition, the chamber fill gas is hot and turbulent and contains debris ions. The debris needs to be removed. The ions increase the gas density, may cluster or form aerosols, and can interfere with the propagation of the laser beams to the target for the next shot. Moreover, the tritium and high-Z hohlraum debris needs to be recovered for reuse. Additionally, the cryogenic target needs to survive transport through the gas mixture to the chamber center. Hence, it will be necessary to clear the chamber of the hot contaminated gas mixture and refill it with a cool, clean gas between shots. The refilling process may create density gradients that could interfere with beam propagation, so the fluid dynamics must be studied carefully. This paper describes an analytic modeling effort to study the clearing and refilling process for the LIFE fusion chamber. The models used here are derived from first principles and balances of mass and energy, with the intent of providing a first estimate of clearing rates, clearing times, fractional removal of ions, equilibrated chamber temperatures, and equilibrated ion concentrations for the chamber. These can be used to scope the overall problem and provide input to further studies using fluid dynamics and other more sophisticated tools.« less