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Tim Elam

Principal Physicist

Email

wtelam@apl.washington.edu

Phone

206-685-3092

Research Interests

X-ray Spectroscopy

Biosketch

Dr. 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 an X-ray fluorescence spectrometer (XRFS) to measure heavy metal contaminants in soils and sediments that is directly pushed via cone penetrometery without drilling. His latest project was a borehole XRFS for use in the Mars Subsurface Access Program and it is now being adapted to make in-situ measurements of diffusion of stable isotopes of nuclear waste elements through native rock without radioactivity. Dr. Elam is also the hardware lead for the APL Ice Diver.

He is Chair of the Denver X-ray Conference, serves on the Advisory Board for X-ray Spectrometry, and is a member of the International Center for Diffraction Data. He 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.

Education

B.S. Physics, Mississippi State University, 1973

M.S. Physics, University of Maryland, 1977

Ph.D. Physics, University of Maryland, 1979

Publications

2000-present and while at APL-UW

Optimized Compton fitting and modeling for light element determination in micro-X-ray fluorescence map datasets

O'Neil, L.P., D.C. Catling, and W.T. Elam, "Optimized Compton fitting and modeling for light element determination in micro-X-ray fluorescence map datasets," Nucl. Instrum. Methods Phys. Res., Sect. B, 436, 173-178, doi:10.1016/j.nimb.2018.09.023, 2018.

More Info

1 Dec 2018

The Planetary Instrument for X-ray Lithochemistry (PIXL) is an X-ray fluorescence instrument scheduled to fly to Mars on NASA's 2020 rover (Allwood et al., 2015). It will be capable of quantifying elements with atomic number of at least 11 using X-ray fluorescence (XRF), but the detector window blocks fluorescence from lighter elements. Important elements otherwise invisible include carbon, oxygen, and nitrogen, which can make up anions in minerals of scientific interest. X-rays scattered by all elements can be detected, so the ratio of Compton to Rayleigh scatter may be measured and used to infer the presence of elements for which there is no detectable fluorescence. We have refined a fundamental parameters model to predict the Compton/Rayleigh ratio for any given composition that can be compared to an experimentally measured ratio. We compare with a published Monte Carlo model (Schoonjans et al., 2012) and to experimental values for a set of seven materials. Compton/Rayleigh ratios predicted by the model are in good, though imperfect, agreement with experimental measurements. A procedure for consistently computing the Compton/Rayleigh ratio from a noisy spectrum has also been developed using a variation on a common background removal method and peak fitting.

An empirical derivation of the X-ray optic transmission profile used in calibrating the Planetary Instrument for X-ray Lithochemistry (PIXL) for Mars 2020

Heirwegh, C.M., W.T. Elam, D.T. Flannery, and A.C. Allwood, "An empirical derivation of the X-ray optic transmission profile used in calibrating the Planetary Instrument for X-ray Lithochemistry (PIXL) for Mars 2020," Powder Diffr., 33, 162-165, doi:10.1017/S0885715618000416, 2018.

More Info

1 Jun 2018

Calibration of the prototype Planetary Instrument for X-ray Lithochemistry (PIXL) selected for Mars 2020 has commenced with an empirical derivation of the X-ray optic transmission profile. Through a straightforward method of dividing a measured "blank" spectrum over one calculated assuming no optic influence, a rudimentary profile was formed. A simple boxcar-smoothing algorithm was implemented to approximate the complete profile that was incorporated into PIQUANT. Use of this form of smoothing differs from the more conventional approach of using a parameter-based function to complete the profile. Comparison of element-specific correction factors, taken from a measurement of NIST SRM 610, was used to assess the accuracy of the new profile. Improvement in the low- to mid-energy portion of the data was apparent though the high-energy region diverged from unity, and thus, requires further refinement.

Low-energy shelf response in thin energy-dispersive X-ray detectors from Compton scattering of hard X-rays

Michel-Hart, N., and W.T. Elam, "Low-energy shelf response in thin energy-dispersive X-ray detectors from Compton scattering of hard X-rays," Nucl. Instrum. Meth. A, 863, doi:10.1016/j.nima.2017.04.039, 2017.

More Info

1 Aug 2017

Silicon drift detectors have been successfully employed in both soft and hard X-ray spectroscopy. The response function to incident radiation at soft X-ray levels has been well studied and modeled, but less research has been published on response functions for these detectors to hard X-ray input spectra above 20 keV. When used with hard X-ray sources a significant low energy, non-peak response exists which can adversely affect detection limits for lighter elements in, for example, X-ray fluorescence spectroscopy. We present a numerical model that explains the non-peak response function of silicon drift detectors to hard X-rays based on incoherent Compton scattering within the detector volume. Experimental results are presented and numerically compared to model results.

More Publications

Inventions

In-Situ Elemental Analyzer Using Wavelength Dispersive X-ray Fluorescence

Record of Invention Number: 48011

Tim Elam, Gerald Seidler

Disclosure

28 Mar 2017

Reactive landing for modification of graphene and other nanocarbon materials

Record of Invention Number: 46967

Tim Elam, Joe Rolfs, Frantisek Turecek, Michael Volny

Disclosure

27 May 2014

Reactive Landing Resistance Biosensors

Record of Invention Number: 45652

Tim Elam, Frantisek Turecek, Michael Volny

Disclosure

8 Jun 2011

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
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