LAUSR

50 Vol. 32, No. 6, 2019, Synchrotron radiation newS Introduction: Challenges New and improved materials, composites, and super-alloys capable of withstanding the anticipated extreme states of fusion reactors, fission reactors (i.e., high-temperature fast reactors) and multi-MW particle accelerators, with the latter facing similarly extreme states to reactors under energetic protons, are continuously sought [1]. Materials structures such as improved reactor steels, super-alloys, and novel composites are continuously being explored to help meet both the challenge of the higher-demand environments and longevity under extreme conditions. Higher fluxes of irradiating species (primarily fast neutrons and energetic protons), extreme temperatures, and aggressively corrosive environments make up the new cocktail of operating conditions these materials must withstand. One of the challenges in characterizing the effects under intense irradiation, high temperatures, and stresses is the establishment of the link between lattice-induced damage and phase transformation under particle irradiation and macroscopic physical properties, which ultimately determine performance in the real environment. With ever increasing irradiation fluxes, dramatic changes in the material properties are expected to occur stemming from the evolution or development of new microstructures. In-situ experimental techniques using high-energy X-rays from synchrotron sources have been utilized to investigate the effects of extreme fluxes of irradiating particles in combination with elevated temperatures, which themselves trigger microstructural transformations, extreme stress states, and aggressive environments on material microstructure. Synchrotron-based characterization techniques such as X-ray diffraction, energy dispersive X-ray diffraction, X-ray absorption spectroscopy (XAS), and small angle X-ray scattering (SAXS) have been used at synchrotron beamlines to investigate these effects. There are several advantages in using X-rays for post-irradiation examination. For example, X-ray scattering of polycrystalline materials, in which category all nuclear materials fall, yields measurements that are more statistically reliable than electron microscopy techniques. Electron microscopy tends to limit characterization to a very small volume/ region, a limitation that hinders the ability to connect the findings to the macroscale characterization. Additionally, flexibility in X-ray energy and technique may provide a reliable path in understanding phase evolution, defect formation, and order within the irradiated microstructure. There is also the advantage of using high-energy X-rays to penetrate macroscopic volumes of the irradiated material, thus allowing for transmission mode diffraction in a bulk sample. Third-generation synchrotron sources produce high-brilliance, hard X-rays that allow non-destructive in-situ measurements with high spatial and temporal resolution. Highenergy X-rays at the BNL synchrotrons, previously at NSLS and now NSLS-II, have been critical in providing a path for establishing the important connection between micro-scale effects and physical properties of novel materials exposed to high radiation fluxes.