X-ray vision: Seeing through the mystery of an X-ray emissions mechanism

Recently, a team of researchers at Penn State University used mathematical modeling to explain the underlying mechanisms at work. They published their results Physical Review Letters.

“In these laboratory experiments, a voltage is applied between two electrodes (electrical conductors). Electrons (negatively charged particles) are then accelerated through a gap (which may be a gas or vacuum),” says electrical professor Victor Pa Victor Pasko said. “The energy an electron can acquire should correspond to the applied voltage, but in all of these experiments the energy exceeded the voltage by two to three times, which was a mystery.”

Through mathematical modeling, Pascoe and his team showed that an energy feedback process is responsible for this.

According to Pascoe, when electrons interact with the electrode material, they emit X-rays composed of photons, the massless, chargeless particles that make up light. Some of these photons travel backward, allowing more electrons to be released from the other electrode. A small fraction of these electrons have an energy corresponding to the original energy. Then they accelerate again, and this process continues for several cycles. Pascoe and his team simulated this very high-energy process.

Pascoe said their model also helps explain why electrodes of different shapes and materials produce this effect to varying degrees.

“We found that the effect was greatest when we used flat electrodes and least when the electrodes were needle-shaped,” Pascoe said. “This makes sense because the large surface area of ​​flat electrodes facilitates the interaction between electrons and photons. The interaction between them and the way they bounce back and forth is minimized when the surface area is reduced.”

The researchers also used simulations and modeling to study how this phenomenon occurs in different materials.

“Tungsten is a standard material used in X-ray production, and we know it’s a good material. It’s a strong material used in the production of electronics used in current X-ray machines,” Pascoe said. “Our research used many other materials, and using our model we were able to summarize the material properties that led to the greatest effect.”

The researchers say their findings could help develop new ways to generate X-rays in the future. Specifically, they say the work could spur new research into generating high-energy electrons from solid materials, potentially making X-ray machines faster, lighter and more compact.

Sebastien Celestin of the University of Orléans in France and Anne Bourdon of the Center National de la Recherche Scientifique and Ecole Polytechnique are co-authors of the paper. The National Science Foundation supported this research in part.