Brittany Muntifering

Cavity Evolution at Grain Boundaries as a Function of Radiation Damage and Thermal Conditions in Nanocrystalline Nickel

Enhanced radiation tolerance of nanostructured metals is attributed to the high density of interfaces that can absorb radiation-induced defects. Here, cavity evolution mechanisms during cascade damage, helium implantation, and annealing of nanocrystalline nickel are characterized via in situ transmission electron microscopy (TEM). Films subjected to self-ion irradiation followed by helium implantation developed evenly distributed cavity structures, whereas films exposed in the reversed order developed cavities preferentially distributed along grain boundaries. Post-irradiation annealing and orientation mapping demonstrated uniform cavity growth in the nanocrystalline structure, and cavities spanning multiple grains. These mechanisms suggest limited ability to reduce swelling, despite the stability of the nanostructure.

Using in-situ TEM Triple Ion Beam Irradiations to Study the Effects of Deuterium, Helium, and Radiation Damage on TPBAR Components

In order to maintain the level of tritium production required for sustaining the nation’s strategic stockpile, Tritium-Producing Burnable Absorber Rods (TPBAR) are placed in nuclear reactors (currently, the TVA Watts Barr reactor). TPBARs consist of a lithium aluminate (LiAlO2) pellet that is surrounded by inner and outer layers of Zircaloy-4; the outer layer acts as a H getter and the inner layer acts to reduce tritium oxide (H2O) emerging from the pellet so that H can be gettered. The LiAlO2 pellet is enriched with the Li isotope, which absorbs neutrons from the reactor, becoming Li, which fissions to H + He in less than 1 s. Tritium will eventually β-decay to He with a half-life of 12.3 years. The bars are surrounded by reactor grade 316 stainless steel cladding with an aluminide coating to prevent inward diffusion of hydrogen from the coolant and outward diffusion of tritium [1]. Predicting the longevity of the TPBAR relies on a thorough understanding of gas behavior and irradiation damage evolution inside both the LiAlO2 pellet and the Zircaloy-4 getter. At sufficiently high concentrations, gas atoms will agglomerate to form bubbles. Defect structures, such as voids and dislocation loops, formed due to neutron irradiation will act as sinks for gas atoms and influence bubble formation kinetics.

In Situ TEM Multi-Beam Ion Irradiation as a Technique for Elucidating Synergistic Radiation Effects

Materials designed for nuclear reactors undergo microstructural changes resulting from a combination of several environmental factors, including neutron irradiation damage, gas accumulation and elevated temperatures. Typical ion beam irradiation experiments designed for simulating a neutron irradiation environment involve irradiating the sample with a single ion beam and subsequent characterization of the resulting microstructure, often by transmission electron microscopy (TEM). This method does not allow for examination of microstructural effects due to simultaneous gas accumulation and displacement cascade damage, which occurs in a reactor. Sandia’s in situ ion irradiation TEM (I3TEM) offers the unique ability to observe microstructural changes due to irradiation damage caused by concurrent multi-beam ion irradiation in real time. This allows for time-dependent microstructure analysis. A plethora of additional in situ stages can be coupled with these experiments, e.g., for more accurately simulating defect kinetics at elevated reactor temperatures. This work outlines experiments showing synergistic effects in Au using in situ ion irradiation with various combinations of helium, deuterium and Au ions, as well as some initial work on materials utilized in tritium-producing burnable absorber rods (TPBARs): zirconium alloys and LiAlO2.

Imaging radiation damage in nanoparticles for radiation therapies (Conference Presentation)

Nanomaterials have shown promise for a variety of medical applications due to their unique properties and form factors compared to their bulk counterparts. Several novel medical technologies leveraging these properties are in various stages of development for applications including drug delivery, anti-microbial, diagnostic, or therapy technologies. A subset of these technologies, namely radiation therapy applications, require the nanoparticles to retain their structure and properties in radiation environments. It has been demonstrated that nanoparticle irradiation response can vary greatly from bulk materials response, as damage effects become dominated by sputtering and surface effects. As such, the stability, or rather the resistance of these materials towards radiation-induced degradation needs to be well understood to gauge the efficacy of candidate nanoparticles for these applications. This presentation details ongoing efforts at the In-situ Ion Irradiation Transmission Electron Microscopy (I3TEM) facility at Sandia National Laboratories to study and characterize the structural evolution of nanoparticles utilizing both in-situ and ex-situ ion beam irradiation techniques. Materials systems of interest include CeO2 nanoparticles, used for protecting healthy cells from radiation damage, and Au and HfO2 nanoparticles, used to increase local dose from proton therapies. Observed nanoparticle responses were varied and included stability, coalescence, ablation, cratering, sputtering, and swelling, depending on particle species, morphology, and irradiation condition. This diversity in nanoparticle irradiation response demonstrates the need for additional systematic study to determine the ultimate usefulness of various nanoparticle species for radiation therapy applications.

Impact of oleylamine: oleic acid ratio on the morphology of yttria nanomaterials

The impact on the final morphology of yttria (Y2O3) nanoparticles from different ratios (100/0, 90/10, 65/35, and 50/50) of oleylamine (ON) and oleic acid (OA) via a solution precipitation route has been determined. In all instances, powder X-ray diffraction indicated that the cubic Y2O3 phase (PDF #00-025-1200) with the space group I-3a (206) had been formed. Analysis of the collected FTIR data revealed the presence of stretches and bends consistent with ON and OA, for all ratios investigated, except the 100/0. Transmission electron microscopy images revealed regular and elongated hexagons were produced for the ON (100/0) sample. As OA was added, the nanoparticle morphology changed to lamellar pillars (90/10), then irregular particles (65/35), and finally plates (50/50). The formation of the hexagonal-shaped nanoparticles was determined to be due to the preferential adsorption of ON onto the {101} planes. As OA was added to the reaction mixture, it was found that the {111} planes were preferentially coated, replacing ON from the surface, resulting in the various morphologies noted. The roles of the ratio of ON/OA in the synthesis of the nanocrystals were elucidated in the formation of the various Y2O3 morphologies, as well as a possible growth mechanism based on the experimental data.

In-Situ TEM Self-Ion Irradiation and Thermal Aging of Optimized Zirlo

The aggressive environments of nuclear reactors present a wide range of material difficulties due, in particular, to neutron radiation and elevated temperatures. Zirconium alloys are commonly used as nuclear fuel cladding due to their nuclear cross-section and high resistance to corrosion; however, neutron irradiation can result in hardening and swelling of zirconium alloys in certain temperature regimes [1]. In this study, we examined the effects of irradiation of commercially available Optimized Zirlo with zirconium ions in order to characterize microstructural evolution as a result of self-ion induced displacement damage. The evolution of the defects was characterized during post-irradiation annealing. Microstructural evolution of grain and precipitate structure and boundaries as a result of irradiation was studied using ASTAR orientation mapping.

In-Situ TEM He+ Implantation and Thermal Aging of Nanocrystalline Fe

A key aspect in predictively modeling the response of materials exposed to many radiation environments is understanding the role of light transmutation products. He in particular can result in the swelling and precipitation of bubbles, both of which can substantially deteriorate the mechanical properties [1]. In this study, in situ TEM characterization of nanocrystalline Fe samples implanted with 10 keV He + is performed to understand and quantify the mechanisms underlying He diffusion and cavity nucleation under a wide temperature range