24.011 How electrons get rid of energy in a flash

APA, Der Standard
Nuclear physics: How electrons get rid of energy in a flash, 11.9.2017
derstandard.at, How electrons get rid of energy in a flash

Nuclear physics

How electrons get rid of energy in a flash

Researchers of the Technical University Vienna solved puzzle about "hollow atoms"

Atoms, the electrons of which show extreme high energies, can emit this energy at contact with other material within shortest time. Researchers of the Technical University (TU) Vienna have now investigated this long baffling effect experimentally with an international team. They report about it in the specialist journal "Physical Review Letters".

In its basic state the electron shell of an atom is filled completely: The electrons shortest of energy are wholly at the inside, close to the nucleus of the atom, while the more energy rich occupy the further outside lying shells, without leaving a gap with it. Under certain circumstance some of the electrons can however also lie much further outside than usually and so let a hollow space be formed, in which no electrons are.

Energy emission in femto seconds

These so-called Rydberg atoms can emit their surplus energy within a few femto seconds (a femto second is adequate to the millionth part of a billionth second), when they come into contact with another material and the electrons which are there. How this process can go so fast, was long unclear.

To go to the bottom of the thing, experiments with rare gas atoms were now carried out at the TU Vienna. For it the researchers removed first up to 40 of the outer electrons of an atom and let it then fly through a graph, an extreme thin material, which consists of only one single layer carbon atoms. Although the crossing of the graph only lasts about one femto second, the atom can then receive a large part of the missing electrons and form one Rydberg atom.

"The strongly positive loaded rare gas atom works thereby like a kind of electron vacuum cleaner", explained the leader of the research group, Friedrich Aumayr of the Institute for Applied of the TU Vienna. "In a flash it withdraws the electrons of the carbon atoms of the graph, which it needs itself, to again be approximately electrically neutral." Almost at the same time the "sucked in" electrons fall back into the basic state and again emit their energy to the electrons remaining in the graph.

Relevance for radiation therapy

With the help of their experiments the researchers could now show that an up to now underestimated effect is responsible for this process - the so-called "Interatomic Coulombic Decay". With it the energy is indeed emitted in small doses, but then to a great number of electrons in the graph, which then fly relatively slowly out of the material.

Since slow electrons are particularly good in the position to break up chemical bonds as for example the DNA cords in cells, this actually rather exotic process is also interesting for biology. With radiation therapy for the fight against cancer cells quite similar effects occur, with the help of which cancer cells are to be particularly effectively damaged. "Our research is therefore also a contribution for the better understanding of already successfully used therapy methods", so Aumayr. (APA, 11.9.2017)

Physical Review Letters: "Interatomic Coulombic Decay: The Mechanism for Rapid Deexcitation of Hollow Atoms"

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