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ePaper created 2014-04-30, 16:22:09 | version 1.30.01
discovered 02 .13 research WWW.Hzdr.DE "It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you." New Zealand physicist Ernest Rutherford described the result of his experiments in these words, after having directed positively charged helium nuclei (alpha particles) at a piece of delicate gold foil. To his great surprise, not all of the particles flew unhindered through the metal foil. Instead, a certain percentage altered their direction of travel or were even reflected. The scattering experiment by Ernest Rutherford roughly 100 years ago marked a turning point in our understanding of atomic structure. His results led to the conception that every atom possesses a very small, positively charged nucleus which is surrounded by negatively charged electrons. As miniscule as an atomic nucleus is, important phenomena are bound up with the processes in the atomic nucleus, like radioactivity and nuclear fission, as well as formation of chemical elements in the stars. For this reason, scientists attempt to find out as many of the details about the structure and reactions of atomic nuclei as possible. Researchers at HZDR are also participating in this effort. Ronald Schwengner and his colleagues are especially interested in what are called dipole resonances in atomic nuclei and their influence on the course of nuclear reactions. Joint research by scientists at the Triangle Universities Nuclear Laboratory (TUNL) in Durham, North Carolina, USA and at HZDR has recently been successful in measuring the magnetic dipole resonance of an atomic nucleus with great accuracy. The new data can be incorporated in calculations pertinent to nuclear astrophysics and nuclear engineering, among other fields. However, just how does one investigate atomic nuclei, those tiny structures of neutrons and protons? "You first have to raise the nuclei into energetically excited states," explains physicist Ronald Schwengner. This takes place by bombarding them with ions, neutrons, or with highly energetic photons (gamma quanta). When the atomic nuclei then fall back to // Experiments at the High-Intensity Gamma-Ray Source HIGS at Durham in the USA have produced detailed values for the magnetic dipole resonance for the first time – thereby revealing details about the structure of atomic nuclei. _TEXT . Uta Bilow Magnetic resonance of atomic nuclei SOURCE OF RADIATION: Gamma rays used in the study of atomic nuclei are produced when fast-moving electrons from the ELBE accelerator hit a special target. This strongly decelerates the electrons, which is why physicists speak of "bremsstrahlung." Photo: Frank Bierstedt