Timothy A. White

Vulnerability of larval and juvenile white sturgeon to barotrauma: can they handle the pressure?

Techniques were developed to determine when fish are vulnerable to barotrauma when rapidly decompressed during hydroturbine passage. Sturgeons were decompressed in early life-stages and X-ray radiographs were taken to determine when gas was present in the swim bladder. Barotrauma was observed on day 9 and greater than 75 days after hatching.

Non-invasive material discrimination using spectral x-ray radiography

Current radiographic methods are limited in their ability to determine the presence of nuclear materials in containers or composite objects. A central problem is the inability to distinguish the attenuation pattern of high-density metals from those with a greater thickness of a less dense material. Here, we show that spectrally sensitive detectors can be used to discriminate plutonium from multiple layers of other materials using a single-view radiograph. An inverse algorithm with adaptive regularization is used. The algorithm can determine the presence of plutonium in simulated radiographs with a mass resolution per unit area of at least 0.07 g cm−2.

Investigating biofilm structure using x-ray microtomography and gratings-based phase contrast

Direct examination of natural and engineered environments has revealed that the majority of microorganisms in these systems live in structured communities termed biofilms. To gain a better understanding for how biofilms function and interact with their local environment, fundamental capabilities for enhanced visualization, compositional analysis, and functional characterization of biofilms are needed. For pore-scale and community-scale analysis (100’s of nm to 10’s of microns), a variety of surface tools are available. However, understanding biofilm structure in complex three-dimensional (3-D) environments is considerably more difficult. X-ray microtomography can reveal a biofilm’s internal structure, but obtaining sufficient contrast to image low atomic number (Z) biological material against a higher-Z substrate makes detecting biofilms difficult. Here we present results imaging Shewanella oneidensis biofilms on a Hollow-fiber Membrane Biofilm Reactor (HfMBR), using the x-ray microtomography system at sector 2-BM of the Advanced Photon Source (APS), at energies ranging from 12.9-15.4 keV and pixel sizes of 0.7 and 1.3 μm/pixel. We examine the use of osmium (Os) as a contrast agent to enhance biofilm visibility and demonstrate that staining improves imaging of hydrated biofilms. We also present results using a Talbot interferometer to provide phase and scatter contrast information in addition to absorption. Talbot interferometry allows imaging of unstained hydrated biofilms with phase contrast, while absorption contrast primarily highlights edges and scatter contrast provides little information. However, the gratings used here limit the spatial resolution to no finer than 2 μm, which hinders the ability to detect small features. Future studies at higher resolution or higher Talbot order for greater sensitivity to density variations may improve imaging.

Phase contrast x-ray imaging signatures for homeland security applications

Gratings-based phase contrast imaging is a promising new radiographic technique providing three distinct contrast mechanisms, absorption, phase, and scatter, using a conventional x-ray tube source. We investigate the signatures available in these three contrast mechanisms with particular attention towards potential homeland security applications. We find that the scatter mode in particular is sensitive to textured materials, enabling lowered detection limits than absorption for materials such as powders. We investigate the length scales to which our imaging system is sensitive.

Phase Contrast X-Ray Imaging Signatures for Security Applications

Differential phase contrast imaging with a grating interferometer is a promising new radiographic technique providing three distinct contrast mechanisms-absorption, phase, and scatter (or dark field)-using a conventional X-ray tube source. We examine the signatures available in these three contrast mechanisms with attention towards potential security applications. We find that the scatter mode is uniquely sensitive to textured materials, potentially leading to enhanced material discrimination through the use of multiple contrast modes. We find that scatter signal in our imaging system increases as texture size is reduced from 800 μm to 7 μm. This range spans the transition from features that are resolved in the image to those residing below the system resolution, and corresponds to length scales of known texture or density variations in several common explosives.

Combining Radiography and Passive Measurements for Radiological Threat Localization in Cargo

Detecting shielded special nuclear material (SNM) in a cargo container is a difficult problem, since shielding reduces the amount of radiation escaping the container. Radiography provides information that is complementary to that provided by passive gamma-ray detection systems: while not directly sensitive to radiological materials, radiography can reveal highly shielded regions that may mask a passive radiological signal. Combining these measurements has the potential to improve SNM detection, either through improved sensitivity or by providing a solution to the inverse problem to estimate source properties (strength and location). We present a data-fusion method that uses a radiograph to provide an estimate of the radiation-transport environment for gamma rays from potential sources. This approach makes quantitative use of radiographic images without relying on image interpretation, and results in a probabilistic description of likely source locations and strengths. We present results for this method for a modeled test case of a cargo container passing through a plastic-scintillator-based radiation portal monitor and a transmission-radiography system. We find that a radiograph-based inversion scheme allows for localization of a low-noise source placed randomly within the test container to within 40 cm, compared to 70 cm for triangulation alone, while strength estimation accuracy is improved by a factor of six. Improvements are seen in regions of both high and low shielding, but are most pronounced in highly shielded regions. The approach proposed here combines transmission and emission data in a manner that has not been explored in the cargo-screening literature, advancing the ability to accurately describe a hidden source based on currently-available instrumentation.

National Security Science and Technology Initiative: Air Cargo Screening, Final Report for CRADA Number NFE-07-01081

The non-intrusive inspection (NII) of consolidated air cargo carried on commercial passenger aircraft continues to be a technically challenging, high-priority requirement of the Department of Homeland Security’s Science and Technology Directorate (DHS S&T), the Transportation Security Agency and the Federal Aviation Administration. The goal of deploying a screening system that can reliably and cost-effectively detect explosive threats in consolidated cargo without adversely affecting the flow of commerce will require significant technical advances that will take years to develop. To address this critical National Security need, the Battelle Memorial Institute (Battelle), under a Cooperative Research and Development Agreement (CRADA) with four of its associated US Department of Energy (DOE) National Laboratories (Oak Ridge, Pacific Northwest, Idaho, and Brookhaven), conducted a research and development initiative focused on identifying, evaluating, and integrating technologies for screening consolidated air cargo for the presence of explosive threats. Battelle invested

A single-pixel X-ray imager concept and its application to secure radiographic inspections

8.5M of internal research and development funds during fiscal years 2007 through 2009.