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Tim Elam

Senior Principal Physicist





Research Interests

X-ray Spectroscopy


Dr. Tim Elam's main research interest is X-ray spectroscopy. He has worked in the areas of X-ray absorption, emission, fluorescence, and non-resonant inelastic scattering. His present efforts focus on using X-ray fluorescence in difficult environments. He has built several downhole X-ray fluorescence spectrometers to measure heavy metal contaminants in soils and sediments and to make in-situ measurements of diffusion of stable isotopes of nuclear waste elements through native rock without radioactivity. He is now the Chief Spectroscopist for the Planetary Instrument for X-ray Lithochemistry (PIXL) on the Perseverance rover and the hardware lead for the APL-UW Ice Diver.

He is past Chair of the Denver X-ray Conference and was the American Institute of Physics Congressional Science Fellow for 1991. He has more than 100 publications in refereed scientific journals and holds 5 patents.

Department Affiliation

Polar Science Center


B.S. Physics, Mississippi State University, 1973

M.S. Physics, University of Maryland, 1977

Ph.D. Physics, University of Maryland, 1979


2000-present and while at APL-UW

Microbial transport by a descending ice melting probe: Implications for subglacial and ocean world exploration

Schuler, C.G., D.P. Winebrenner, W.T. Elam, J. Burnett, B.W. Boles, and J.A. Mikucki, "Microbial transport by a descending ice melting probe: Implications for subglacial and ocean world exploration," Astrobiology, EOR, doi:10.1089/ast.2021.0106, 2023.

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6 Jun 2023

Ocean Worlds beneath thick ice covers in our solar system, as well as subglacial lakes on Earth, may harbor biological systems. In both cases, thick ice covers (>100 s of meters) present significant barriers to access. Melt probes are emerging as tools for reaching and sampling these realms due to their small logistical footprint, ability to transport payloads, and ease of cleaning in the field. On Earth, glaciers are immured with various abundances of microorganisms and debris. The potential for bioloads to accumulate around and be dragged by a probe during descent has not previously been investigated. Due to the pristine nature of these environments, minimizing and understanding the risk of forward contamination and considering the potential of melt probes to act as instrument-induced special regions are essential. In this study, we examined the effect that two engineering descent strategies for melt probes have on the dragging of bioloads. We also tested the ability of a field cleaning protocol to rid a common contaminant, Bacillus. These tests were conducted in a synthetic ice block immured with bioloads using the Ice Diver melt probe. Our data suggest minimal dragging of bioloads by melt probes, but conclude that modifications for further minimization and use in special regions should be made.

Experimental validation of cryobot thermal models for the exploration of ocean worlds

Pereira, P.D., and 19 others including D.P. Winebrenner and W.T. Elam, "Experimental validation of cryobot thermal models for the exploration of ocean worlds," Planet. Sci. J., 4, doi:10.3847/PSJ/acc2b7, 2023.

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5 May 2023

Accessing the potentially habitable subsurface waters of Ocean Worlds requires a robotic ice probe (or "cryobot") to traverse tens of kilometers of ice with temperatures ranging from ~100 to 273 K. Designing and planning such a mission requires understanding ice probe behavior as a function of the local environment and design parameters. We present experimental results of two laboratory melt probes in cryogenic (79 K) and warm (253 K) ice. The melt probe tested in warm ice had multiple adjustable heaters, enabling optimization of the system's efficiency. The melt probes tested in cryogenic ice operated in vacuum and had internal tether spools, allowing for experimental confirmation of hole closure and the creation of a pressurized pocket with liquid water around the probe. These melt probes were tested at power levels ranging from 120 to 1135 W, achieving descent speeds between 5.3 and 59 cm hr-1. By analyzing the relationship between power and speed using analytical and high-fidelity numerical models, we demonstrate progress in understanding melt probe performance. We distinguish between the previously confounding terms of probe operational inefficiency and analytical model inaccuracy, allowing us to understand the range of applicability of the analytical models and demonstrate the importance of controlling heat distribution in cryobot design. The validated models show that while numerical models may be required to describe the behavior of short probes descending in limited-size laboratory test beds, the performance of efficient cryobots designed for operation on Ocean Worlds can be predicted by analytical models within 5% error.

A statistical approach to removing diffraction from X-ray fluorescence spectra

Orenstein, B.J., D.T. Flannery, L.W. Casey, W.T. Elam, C.M. Heirwegh, M.W.M. Jones, "A statistical approach to removing diffraction from X-ray fluorescence spectra," Spectrochim. Acta, Part B, 200, doi:10.1016/j.sab.2022.106603, 2023.

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1 Feb 2023

Diffraction peaks can lead to inaccurate elemental abundances in X-ray fluorescence maps. However, manually removing diffraction peaks is laborious while existing automated methods unnecessarily remove significant volumes of fluorescence data. Here we propose a new automated method to remove diffraction from multiple-detector spectra based on a statistical threshold. This method eliminates only the diffraction peaks from the spectra, retaining more of the fluorescence data and increasing the information content available for diffraction-free elemental quantification and mapping. By retaining the majority of the fluorescence data, the proposed method does not require an increase in dwell times or additional data to be collected to compensate for the removed fluorescence data. This method is therefore particularly valuable in instances where measurement time and data volumes are highly restricted, such as for instruments on planetary exploration missions like the Planetary Instrument for X-ray Lithochemistry on NASA's Mars 2020 mission Perseverance Rover.

More Publications

Acoustics Air-Sea Interaction & Remote Sensing Center for Environmental & Information Systems Center for Industrial & Medical Ultrasound Electronic & Photonic Systems Ocean Engineering Ocean Physics Polar Science Center