Groundbreaking Atomic 'Movie' Reveals Dynamic Mechanism of Radiation Damage

For the first time, scientists have captured atomic motion in a 'movie,' observing atoms 'roam' for a picosecond before a radiation-induced decay. This unprecedented view uncovers a previously hidden, dynamic driver of radiation damage at the atomic level.

The research focuses on electron-transfer-mediated decay (ETMD), a process where radiation excites an atom, which then stabilizes itself by taking an electron from a neighbor, leading to the ionization of a third atom and subsequent atomic fragmentation. This mechanism is crucial as it generates highly reactive particles, particularly in water, making it a significant contributor to radiation damage in biological systems.

Utilizing a specialized COLTRIMS reaction microscope coupled with advanced theoretical simulations, researchers precisely tracked this decay in a carefully controlled model system, effectively creating a real-time 'movie' of atomic movement. This 'movie' revealed atoms constantly shifting and reorganizing for up to a picosecond before the system broke apart, demonstrating that radiation damage is a dynamic, continuously evolving process, not a static event. These findings provide critical insights into the atomic-level development of radiation damage, paving the way for improved models of radiation effects in biological environments and potentially guiding the development of new protective strategies.

How Radiation Damages Cells at the Atomic Level

High-energy radiation, such as X-rays, poses a threat to living cells by disrupting atoms and molecules. This disturbance can excite particles, causing them to break down and potentially destroy vital biomolecules, thus compromising biological systems. Understanding the various decay processes is key to comprehending radiation damage and developing mitigation strategies.

A recent international study delved into electron-transfer-mediated decay (ETMD). This intricate process begins when radiation excites one atom. To stabilize, this atom extracts an electron from a neighboring atom, using the released energy to ionize a third. The team's breakthrough was directly observing the atomic reorganization and shifting within a model system before this decay, offering the most detailed real-space and real-time perspective of ETMD to date.

Tracking Atomic Motion in Real Time

To achieve this, researchers employed a simple NeKr2 trimer (one neon atom weakly bonded to two krypton atoms) as their model. Soft X-rays were used to eject an electron from the neon atom, after which the system's evolution was tracked for an unprecedented picosecond – an exceptionally long duration on the atomic scale – until decay occurred. During this interval, an electron transfer and low-energy electron emission took place.

By integrating an advanced COLTRIMS reaction microscope at BESSY II (Berlin) and PETRA III (Hamburg) synchrotron facilities with detailed ab initio simulations, they meticulously reconstructed the atomic arrangements at the decay moment and modeled thousands of potential atomic pathways, assessing decay probabilities for each.

A 'Movie' of Atoms on the Move

The results unveiled a surprising dynamism: atoms were not static. Instead, they exhibited a 'roaming' pattern, continually altering positions and reshaping the system's structure. This constant motion profoundly influenced both the timing and ultimate outcome of the decay.

"We can literally watch how the atoms move before the decay happens," noted Florian Trinter, one of the lead authors. He emphasized that "The decay is not just an electronic process -- it is steered by nuclear motion in a very direct and intuitive way."

The research indicates that ETMD doesn't stem from a single, stable structure. Instead, different atomic arrangements govern decay at various points in time. Initially, decay occurs close to the original configuration. Subsequently, one krypton atom approaches the neon atom while the other recedes, fostering optimal conditions for electron transfer and energy flow. Later still, atoms adopt more elongated and distorted forms, indicative of a swinging, roaming movement. These geometric shifts lead to significant variations in the decay rate.

Till Jahnke, the senior author, stated, "The atoms explore large regions of configuration space before the decay finally takes place." He concluded, "This shows that nuclear motion is not a minor correction -- it fundamentally controls the efficiency of non-local electronic decay."

Why Understanding ETMD Matters

ETMD is gaining considerable attention due to its generation of low-energy electrons, known to induce chemical damage in liquids and biological tissues. A comprehensive understanding of how this process is influenced by atomic arrangement and motion is crucial for accurate modeling of radiation damage in water and biological settings, and for interpreting ultrafast X-ray experiments. Furthermore, these findings aid in developing theoretical models applicable to more intricate systems.

By establishing a precise benchmark for the simplest three-atom ETMD system, this study lays the groundwork for applying these concepts to liquids, solvated ions, and complex biological structures.

"This work shows how non-local electronic decay can be used as a powerful probe of molecular motion," the authors concluded, emphasizing that it "opens the door to imaging ultrafast dynamics in weakly bound matter with unprecedented detail."