191023-N-NO204-003 WASHINGTON (Oct. 23, 2019) Evan Groopman, left, a research physicist and Dr. David Willingham (right), a research chemist and head of the Accelerator Mass Spectrometry Section, gather in front of the NAUTILUS instrument in the Accelerator Mass Spectrometry Laboratory at the U.S. Naval Research Laboratory in Washington D.C., Sept. 5. (U.S. Navy photo by Daniel Perry/Released)