How are electrons formed 1

How are free electrons created?

New type of generation of slow electrons proven / explanation for biological radiation damage?

Scientists at the Max Planck Institute for Plasma Physics (IPP) in Garching / Greifswald and the Fritz Haber Institute in Berlin have discovered a previously unknown way in which high-energy radiation can release slow electrons in water. The results have now been published in the renowned journal "Nature Physics". Free electrons play a major role in chemical processes. In particular, they could be important for the development of radiation damage in organic tissue.

When ionizing radiation hits matter, large amounts of slow electrons are always released. Up until now it was assumed that the high-energy radiation knocked these electrons out of the electron shell of the hit particles - for example from a water molecule. In their experiment, the Berlin scientists shot at so-called water clusters, tiny lumps of ice, with soft X-rays from the BESSY synchrotron radiation storage ring in Berlin. As expected, they detected the known electrons. In addition, however, a new process emerged: Two neighboring water molecules work together to increase the yield of slow electrons.

First, the energy of the X-rays is absorbed in the material: A water molecule is ionized and releases an electron. However, this electron does not take with it the entire energy of the X-ray photon that has hit it. A remainder remains stored in the remaining ion and ensures that a further electron is released a few femtoseconds later. (A femtosecond is a millionth of a billionth of a second. For example, it takes a few femtoseconds for electrons to rearrange themselves in a chemical process.) This process is known as autoionization - the molecule ionizes itself.

The Max Planck researchers have now discovered that two neighboring water molecules can work together in such an autoionization process. Together they reach a state that is energetically more favorable for both if they both release an electron. To do this, the first molecule ion generated transfers its excess energy to a second molecule, which then sends out its own electron. This energy transfer even works through the empty space, a chemical bond between the two molecules is not necessary.

The discovery is not entirely surprising. More than ten years ago, theorists at Heidelberg University working with Lorenz Cederbaum predicted this "intermolecular Coulomb decay". It has already been observed in frozen noble gases. In order to find it unequivocally in water, a sophisticated experimental technique was required in which both electrons generated are detected as a pair.

The proof of the IPP researchers that the process is possible in water - i.e. also in organic tissue - could help to explain the origin of radiation damage. “Slow electrons released in an organism can have fatal consequences for biologically relevant molecules,” explains Uwe Hergenhahn from the Berlin IPP working group at BESSY: “It has only been known for a few years that the accumulation of such electrons can split organic molecules like scissors into two pieces can divide. Very little is known about how this and other processes at the molecular level cause radiation damage. It is clear, however, that this is an important field of research. ”But intermolecular Coulomb decays are also important for other processes in chemistry: The paired cooperation of a water molecule with a substance dissolved in water could clarify how dissolution processes on molecular ones Work level.

The results of the IPP researchers were recently published in the renowned journal "Nature Physics". At the same time, a complementary experiment is documented there, in which a working group from the University of Frankfurt was able to see intermolecular Coulomb decays in the smallest possible water clusters, consisting of only two water molecules.

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