Nuclear materials, such as those used in nuclear reactors and waste forms, are subjected to extreme environments on long timescales. Nuclear reactors need to operate safely for decades, and next generation reactors will only require even more durable materials than those currently in use. Nuclear waste, which currently has no long term disposal plan in the United States, is required to be safely isolated for one million years. Designing and testing materials used for waste packaging is critical to the overall goal of safe storage. A deeper understanding of the bahvior of actinide-bearing materials in extreme environments is necessary in order to accomplish these goals.
Specifically, our research interests lie in understanding and quantifying the changes that materials go through when they experience the combination of radiation fields, high pressures, and high temperatures common in nuclear environments. To do this, we utilize a variety of techniques that drive materials to these extreme conditions. Swift heavy ions (SHIs) are used mimic the damage cause by fission fragments in reactors and alpha particles in waste forms. Ultrafast lasers, which interact with materials in a very similar way to SHIs, are used as a complementary experimental technique since they allow for shorter experiment time and for the ability to conduct pump-probe experiments. Diamond anvil cells (DACs) are used to understand the response of materials to pressures in excess of 100 GPa. DACs can be further coupled to other extreme conditions. Laser heating systems, which heat samples to over 4000 K, allow for the study of materials at simultaneous high pressure and high temperature, and SHIs and ultrafast lasers can both irradiate materials pressurized in a DAC.
We employ a number of experimental techniques to analyze the structure of materials in extreme environments. Raman spectroscopy is used to understand distortions in the local coordination of atoms. Synchrotron light sources provide high brilliance X-rays in order to conduct X-ray diffraction experiments to understand the long-range order of materials. The facilities at the Linac Coherent Light Source at SLAC National Accelerator Facility can be used to probe materials using ultrafast X-ray bunches that provide a mixture of spatial and temporal resolution unmatched anywhere else in the country.
Professor Ewing's old group website through the University of Michigan can be found here.