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Materials Science at Oregon State University

Graduate Student Seminars

Date: Thursday, May 18th
Presenter: Ian Love and Catherine Disney, OSU Materials Science


Ian Love (advisor Prof. Julie Tucker) - Prompt Gamma Neutron Activation Analysis of Niobium for Characterization of Light Interstitials

High purity niobium metal is used in the construction of superconducting radio frequency (SRF) cavities in superconducting particle accelerators, such as the Large Hadron Collider (LHC) at CERN or the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory. The usual method for characterizing the impurities in this niobium, the residual resistivity ratio (RRR) technique, can provide information relating to the superconducting quality of the material, and thus, a measure of the impurity content that is not specific to chemical elements. To improve the material quality further, another method, Prompt Gamma Neutron Activation Analysis (PGNAA), must be used to specifically identify the elemental impurities at parts per million (ppm) levels. This study investigates the use of PGNAA for the application of high purity niobium metal, through the use of the PGNAA facility at the Oregon State University TRIGA Reactor (OSTR). Two standard samples were used to determine the analytical sensitivity of the facility, and five “unknown” samples were analyzed to determine the ability of the PGNAA technique to identify impurities known as light interstitials (H, C, N, and O). The PGNAA technique shows promise in this application, with results on the order of magnitude of current chemical analysis techniques.

Ian Love graduated in 2014 from Houghton College with a Physics BS, with a research focus on nuclear physics experiments in support of the National Ignition Facility at Lawrence Livermore National Laboratory. He completed an MS in Materials Science in 2016 at Oregon State University under the advisement of Dr. Julie Tucker. The focus of research for his master's degree was the use of prompt gamma neutron activation analysis for characterization of impurities in niobium metal.

Catherine Disney (advisor Prof. Brian Bay) - 3D Structural and Mechanical Characterisation of the Intervertebral Disc

Intervertebral discs (IVDs) provide flexibility in the spine whilst supporting body weight and transmitting load. Degeneration of the IVD is associated with chronic low back pain which affects ~70% of the population at some point in their lives. Current treatments are limited and are often confined to symptomatic relief. In order to understand the pathological mechanisms of IVD degeneration and design replacement tissues it will be necessary to understand the 3D structure and mechanical behaviour of the disc. Current methodologies for 3D imaging of tissues at microscopic length scales are either limited to small/transparent specimens or require destructive sectioning which leads to artefacts. In contrast, X-ray micro tomography (microCT) is capable of visualising the 3D microstructure of intact samples.

Our work aims to use synchrotron-based microCT: i) to resolve the 3D microstructure of the bovine IVD and ii) to quantify and map the 3D mechanical effects of compressive load on the IVD using digital volume correlation (DVC).

Both paraffin embedded and fresh IVD specimens were imaged using in-line phase contrast at the Diamond-Manchester beamline at the Diamond Light Source synchrotron. Additionally, fresh tissue quadrants were imaged on the same beamline either unloaded or following sequential compression.

Major anatomical structures (nucleus pulposus, annulus fibrosus and constituent lamellae) were resolved. Finer structural details including collagen fibre orientation and cross-bridges could also be identified. Importantly it was possible to image weakly attenuating fresh tissue using phase contrast microCT. Using these approaches we can quantify the 3D displacement of features and map local strain in the IVD. These experiments demonstrate that it is possible to use microCT to characterise the 3D microstructure of fresh IVD in response to load. In future experiments we will characterise the structure and mechanics of injured discs and potential tissue replacements.

Catherine is a third year Regenerative Medicine PhD student from the University of Manchester visiting OSU on a research placement with Brian Bay. So far her PhD has involved optimising microCT imaging (lab and synchrotron) to visualise intervertebral disc microstructure. More recently her work has focussed on imaging compressed samples and analysis to quantify local strain using digital volume correlation. She is excited to apply these imaging and analysis methods in future work to provide new insights into 3D IVD local mechanics, design framework for scaffolds and to assess constructs in situ under compression.