An international team of scientists has blazed a new trail for studying how atoms respond to radiation, by tracking the energetic movement of electrons when a sample of liquid water is blasted with X-rays.
The experiment, described in this week’s issue of the journal Science, required “freezing” the motion of the atoms with which the electrons were associated, on a scale of mere attoseconds. An attosecond is one-quintillionth of a second — or, expressed another way, a millionth of a trillionth of a second.
Attosecond-scale observations could provide scientists with new insights into how radiation exposure affects objects and people.
“What happens to an atom when it is struck by ionizing radiation, like an X-ray? Seeing the earliest stages of this process has long been a missing piece in understanding how radiation affects matter,” Xiaosong Li, a chemistry professor at the University of Washington and a laboratory fellow at the Pacific Northwest National Laboratory, said in a UW news release. “This new technique for the first time shows us that missing piece and opens the door to seeing the steps where so much complex — and interesting — chemistry occurs!”
Li is one of the senior authors of the Science paper, which describes a technique known as X-ray attosecond transient absorption spectroscopy, or AX-ATAS. The technique uses one X-ray pulse to excite atoms, and follows that with another pulse to probe how the excited atoms responded.
For their experiment, the researchers blasted a thin sheet of water with X-ray laser pulses at the SLAC National Accelerator Laboratory’s Linac Coherent Light Source in California. The AX-ATAS method made it possible for them to track the electrons energized by the X-rays as they moved into an excited state, all before the bulkier atomic nuclei had time to move and blur the picture.
“We now have a tool where, in principle, you can follow the movement of electrons and see newly ionized molecules as they’re formed in real time,” Linda Young, another senior study author who is a professor at the University of Chicago and a distinguished fellow at Argonne National Laboratory, said in a PNNL news release.
Li and Young are among 26 authors of the study published by Science, titled “Attosecond-Pump Attosecond-Probe X-Ray Spectroscopy of Liquid Water.” The authors based in Washington state include Li as well as Carolyn Pearce (PNNL and Washington State University) and Emily Nienhuis (PNNL), Lixin Lu, one of the paper’s principal authors, conducted research for the study as a UW doctoral student and is now a postdoctoral researcher at Stanford. Check out the news releases from UW and PNNL for further details about the study.
