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Title: High energy x-ray and neutron studies of disordered energy-related materials at extreme conditions

The fundamental scientific accomplishments are: (1) advances in a general description of the liquid state by employing structural models constrained by measurements to interpret experimental results and extend them to liquids in general, with special emphasis on (2) The structure of the high-temperature crystal and molten UO2 and 3) water. Specifically, samples of UO2 and water were probed using high-energy x-rays at the Advanced Photon Source. The high Z of UO2, and the 2-3mm diameter droplet shape of the molten sample, means that >100keV X-rays are required to minimize absorption and multiple scattering, which can distort the measured structure factor. A high flux of x-rays is also required to obtain sufficient statistical accuracy in short (a few seconds) measurement times. The scattered x-ray data were analyzed and pair distribution functions, extracted that characterize the local and long-range atomic structure of the material. The measurements of the hot UO2 solid show a substantial increase in oxygen disorder and, upon melting, the average U-O coordination was found to decrease from 8 to 6.7±0.5. The research incorporated development of diffraction techniques, sample environment optimization and state-of-the-art simulation techniques. The symbiotic nature of the advances in simulation and experiment allowed for a more focusedmore » and informed development of future experiments, effective use of expensive beam time and generated new research agendas for the growing number of research groups, within the US and internationally, that focus on the structure of liquids. Molecular dynamics (MD) provided detailed information when combined with high-quality XN data including addressing key issues in liquids; the relationship between cooling path, structure and fictive temperature, and the trade-offs between network over connectedness in liquids containing low-coordination cations.« less
Authors:
 [1]
  1. Stony Brook Univ., NY (United States)
Publication Date:
OSTI Identifier:
1253622
Report Number(s):
DOE--SBU-46650
TRN: US1700198
DOE Contract Number:
SC0002510
Resource Type:
Technical Report
Research Org:
Stony Brook Univ., NY (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 36 MATERIALS SCIENCE; 11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS; URANIUM DIOXIDE; NEUTRONS DIFFRACTION; LIQUIDS; DISTRIBUTION FUNCTIONS; WATER; TEMPERATURE RANGE 1000-4000 K; KEV RANGE 100-1000; X-RAY DIFFRACTION; MOLECULAR DYNAMICS METHOD; COORDINATION NUMBER; STRUCTURE FACTORS; DROPLETS; MELTING; SIMULATION; STRUCTURAL MODELS; CRYSTALS; SOLIDS