Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

Lawrence T. Hudson (Fed)

Since 1990, Larry Hudson has performed as a physicist at the National Institute of Standards and Technology (NIST). Dr. Hudson's career began in the 1980s as a NASA-Houston flight controller for the U.S. Space Shuttle Orbital Flight Test Program (STS-1 to 4) before attending graduate school at Vanderbilt University with NASA support to work on radiation interactions with surfaces in the space environment. Later at NIST, as an NRC postdoctoral fellow, this theme continued with work on the pre- or post-flight calibrations of five x-ray astronomy platforms with NASA (BBXRT, ASTRO-D, AXAF-I, AXAF-S, and XTE).

At NIST Hudson leads a program that produces custom-designed calibrated curved-crystal spectrometers that are fielded to help characterize the performance and spectra from exotic x-ray sources including the electron beam ion trap, the electron cyclotron resonance ion source, advanced medical radiography sources, laser-produced plasmas, terawatt pulsed accelerators, ultrafast Petawatt lasers, and inverse-Compton backscatter sources. This and related work have produced over 120 archival publications accruing 100 citations per year according to Google Scholar. Rooted in a culture of instrument making and an infrastructure of fundamental precision metrology development, Hudson has led a project to measure absolute x-ray wavelengths at the femtometer level in support of high-accuracy transfer standards needed in fundamental and applied spectroscopy experiments around the world. These wavelength-dispersive techniques, traceable to the SI, have led to collaborations with the complementary NIST advances in energy-dispersive x-ray detection. Relatedly, a recent publication quoted in the Mise en pratique SI 9th edition (2019), based upon the decades of NIST x-ray metrology, designates the silicon {220} lattice spacing as a secondary definition of the meter.

After the deliberate contamination of the U.S. mail with anthrax, Dr. Hudson assisted in design and coordination of experiments for the White House Task Force on Mail Irradiation resulting in the development of the protocol still in use to sanitize government mail with industrial x-ray sources (recognized with 2003 DoC Bronze Medal). With the sponsorship of the U.S. Department of Homeland Security, Hudson currently serves as the NIST project leader for the development of national and international measurement standards needed to test and evaluate the technical performance and radiation safety of the nation's x-ray and gamma-ray security screening systems in all venues in which they are deployed. This is accomplished through a corpus of new documentary standards, test methods, test artifacts, dosimetry protocols and technical guidance documents, supported by NIST measurement science and computational modeling. This work fills well-documented gaps in transportation and commercial security that have been highlighted in Executive and Legislative requirements for 100 % screening of baggage, cargo, and airline passengers.

Recent Recognitions include Department of Commerce Silver Medals in 2018 and 2020 for homeland security and x-ray metrology, respectively.


Absolute energies and emission line shapes of the x-ray lines of lanthanide metals

Joseph Fowler, Galen O'Neil, Bradley K. Alpert, Douglas Bennett, Edward V. Denison, William Doriese, Gene Hilton, Lawrence T. Hudson, Young I. Joe, Kelsey Morgan, Daniel Schmidt, Daniel Swetz, Csilla I. Szabo-Foster, Joel Ullom
We use an array of transition-edge sensors, cryogenic microcalorimeters with 4 eV energy resolution, to measure the x-ray emission-line profiles of four

The Molybdenum K-shell X-ray Emission Spectrum

Marcus H. Mendenhall, Lawrence T. Hudson, Csilla I. Szabo-Foster, Albert Henins, James P. Cline
Abstract We present newly measured spectra of the X-ray emission of a molybdenum metal anode subject to electron bombardment, using a very high dispersion

Contemporary x-ray wavelength metrology and traceability

Lawrence T. Hudson, James P. Cline, Albert Henins, Marcus H. Mendenhall, Csilla I. Szabo-Foster
We report recent advances in absolute x-ray wavelength metrology in the context of producing modern standard reference data. Primary standard x-ray wavelengths
Created September 24, 2019, Updated September 7, 2022