Scientists discover new model for radiation effects in water systems

What happens when radiation hits water? It’s a question that comes up every time you get an x-ray at the doctor’s office, since you’re mostly made of water. A team of theoretical physicists from DESY worked on data collected by colleagues at Argonne National Laboratory in the United States at the LCLS X-ray laser in California to get a better answer to this question.

What they discovered could settle a controversy in physics over the presence of free electrons in water and how they behave on very short time scales: the electrons, not bound to atoms, are sequestered in bubbles in cage-like structures between individual water molecules. These results are reported in the Journal of the American Chemical Society.

Free electrons are electrons that are not attached to atoms. In water that comes into contact with radiation, free electrons emerge from the water molecules when they are ionized by the radiation. How electrons flow between water molecules in this situation has been a topic of discussion for a longer time.

In their work at SLAC National Accelerator Laboratory’s LCLS, the experimental team, led by Argonne scientist Linda Young, observed strange signatures associated with water molecules excited by the lasers and imaged by the laser at X-rays. They found structures among the molecules using X-ray absorption spectroscopy. To better understand the significance of these results, the experimental team turned to theoretical physicists in Hamburg.

A team led by DESY scientist Ludger Inhester of the Center for Free Electron Laser Science examined the data and began creating models from the data in coordination with the experimental team. Together, their results show that free electrons in water form bubble structures that are then trapped by water molecules, similar to how chemicals are solvated in water at the molecular level. The DESY team notably succeeded in showing the process behind this solvation of electrons in water and its parameters.

“It turns out that the dissolution process and thus the formation of the cage structures are remarkably sensitive to changes in water temperature,” explains Arturo Sopena, the first author of the study.

New insights into the solvation process show that the electron, which can first be found over a wide area among water molecules, anchors to specific hydrogen bonding patterns that occur in liquid water molecular, then “buries” deeper into a very narrow area. area located inside the aquatic structure.

This “burying” and associated reorientation of neighboring water molecules occurs remarkably quickly and is accomplished within 100 femtoseconds, where one femtosecond is equivalent to one quadrillionth of a second. The bubble, which is about 50 billionths of a meter wide, breaks apart in a few picoseconds, or a trillionth of a second.

“How does water react when exposed to radiation? This is a vital question,” says Inhester. “These are the first chemical reaction steps that are driven by radiation and also determine the subsequent radiation chemistry, which also applies to biological material.”

The new work was also carried out as part of the CUI: Advanced Imaging of Matter cluster of excellence at the Universität Hamburg. The new findings provide additional insight into the damage behavior of ionizing radiation in water. Such water-related research is to be further intensified within the new Center for Molecular Water Sciences, which is being established as part of an international cooperation on the DESY campus.