![]() |
Tim Elam Senior Principal Physicist wtelam@apl.washington.edu Phone 206-685-3092 |
Research Interests
X-ray Spectroscopy
Biosketch
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.
Education
B.S. Physics, Mississippi State University, 1973
M.S. Physics, University of Maryland, 1977
Ph.D. Physics, University of Maryland, 1979
Projects
![]() |
Borehole X-Ray Fluorescence Spectrometer (XRFS) The XRFS was built by APL-UW under a NASA contract from the Langley Research Center; it is designed to be deployed down a pre-drilled hole for exploration and elemental analysis of subsurface planetary regolith. |
|
![]() |
Videos
![]() |
PIXL Blasts Off for Mars PIXL is an X-ray spectrometer integrated into the Perseverance rover that began its journey on July 30th. After landing in early 2021, PIXL will measure the microstructure of rocks in search of fossils and evidence of ancient Martian microbial life. |
15 Sep 2020
|
![]() |
![]() |
PIXL on Mars 2020 Mission PIXL is the Planetary Instrument for X-Ray Lithochemistry. APL-UW's Tim Elam, the mission's 'chief spectroscopist', is collaborating with a NASA team to integrate a micro X-ray fluorescence instrument on a rover that will blast off for Mars in 2020. |
More Info |
24 Feb 2016
|
![]() |
|||||
PIXL's purpose is to measure the microstructure of rocks in search of fossils -- biosignatures of life forms preserved in the rocks. PIXL will tell scientists the composition of materials and their structure -- that is, how the elements are arranged. It's this map of elemental spatial distribution that's critical for finding biosignatures. |
![]() |
Ice Diver: A Thermal Ice Penetrator Ice Diver is a thermal melt probe system for extensive, low-cost sensor deployment to the bed of the Greenland Ice Sheet, where it will measure water pressure in subglacial hydrological networks. |
23 May 2013
|
![]() |
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. |
In The News
![]() |
NASA's Mars Perseverance rover mission serves as ultimate test for working from home (planet) GeekWire, Alan Boyle Tim Elam is an expert on X-ray fluorescence at UW’s Applied Physics Laboratory. So when scientists and engineers were brought onto the team for Perseverance’s Planetary Instrument for X-ray Lithochemistry, or PIXL, Elam was a natural addition. |
29 Jul 2020
|
![]() |
Inventions
![]() |
Thermal Ice Melt Probe Including Water Jetting and Clean Sampling Record of Invention Number: 49014 |
Disclosure
|
13 Jul 2020
|
![]() |
![]() |
PIQUANT X-ray Fluorescence Quantification Software Record of Invention Number: 48292 |
Disclosure
|
27 Mar 2018
|
![]() |
![]() |
In-Situ Elemental Analyzer Using Wavelength Dispersive X-ray Fluorescence Record of Invention Number: 48011 Tim Elam, Gerald Seidler |
Disclosure
|
28 Mar 2017
|
![]() |