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Siegbahn (Siegbahn), Kai

( Swedish physicist, Nobel Prize in Physics, 1981)

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Biography Siegbahn (Siegbahn), Kai
genus. April 20, 1918
Swedish physicist Kai Siegbahn Siegbahn was born in Lund and was the youngest of two sons, Manne Siegbahn and Karin (nee Hegbom) Siegbahn. After graduating from high school in Uppsala 1936. he entered the University of Uppsala, where he studied physics, chemistry and mathematics, and in 1942. received a master's degree. From 1942 to 1951. S. has served as an assistant researcher at the Nobel Institute for Physics in Stockholm, while continuing to work on my dissertation at Stockholm University, which protects in 1944, received his doctorate. His thesis is dedicated to the beta decay (electron emission) of radioactive nuclei. In 1951, Mr.. S. appointed professor of physics at the Royal Institute of Technology in Stockholm and remains in office until his return in 1954. at Uppsala University as a professor of Physics and Mathematical Physics Department of the sector.
The first work with. devoted to electron spectroscopy - the determination of the energies of electrons emitted by atoms. Some of these electrons are beta radiation during radioactive decay of nuclei of several types of. Since the electron energy associated with the energy difference between nuclear states before and after the collapse, the exact knowledge of the electron energy is key to the nuclear structure.
. The emergence of other electrons not directly related to the primary beta-decay, but due to a phenomenon known as internal conversion
. The emission of beta rays leaves the nucleus to the excited level, . from which it then moves to a less excited level, while the energy difference between the two levels is released as gamma rays (electromagnetic radiation, . similar light and X-rays, . but differs more energy and, . hence, . frequency),
. The founder of quantum theory of Max Planck showed, . that electromagnetic radiation consists of discrete portions of energy (which Albert Einstein called quanta, they are now in the case of electromagnetic energy called photons) and that the frequency is proportional to the photon energy,
. Later, Einstein explained the details of the photoelectric effect (emission of electrons of the metal surface, . on which the incident electromagnetic radiation) in terms of photon absorption, . energy is large enough to overcome the energy, . bonding electrons of an atom, . and, . hence, . able to release electrons,
. When the internal conversion of gamma radiation emitted by the nucleus, does not leave the atom and knocks electrons orbiting the nucleus, electrons are knocked-out mixed with the primary beta-radiation. To investigate the energy levels of the kernel, you need to know as a primary energy beta radiation, and secondary photoelectrons.
Accurate measurement of energies hindered limited opportunities acted upon equipment. There are two methods of measuring the energy. In the first method used a uniform magnetic field (this field is created, for example, between the poles of a large flat magnet). Moving electrons generate a magnetic field. The interaction between this field and the external magnet forces the electrons to move in planes parallel to the poles of a magnet, in circles whose diameters zavisyag the speed of electrons. The faster the electrons move, the greater the diameter of the circles. Consequently, this system allows you to sort the electron energy. The second method is to use a system of magnets forming a magnetic focusing lens. The first method gives a good resolution, but low intensity. The second method allows focusing the electron beam to achieve high intensities, but gives poor resolution. Together with his staff Niels C. Svartholm fortress, using the mushroom-shaped magnet, developed a method allowing to focus the electron beam in two directions - in the plane of the circular trajectory and at right angles to it. This method, known as the double magnetic focusing and to achieve high-intensity combined with much higher resolution, soon became widespread.
In the early 50-ies. S. had to wait for long periods of radioactive samples, as well as preparing them for a cyclotron, is working very insecure mode. Reflecting on, . whether it is possible to simulate the radioactive radiation of some other, . more easily controlled way, . He thought of a scheme to install, . which proved to be convenient for the study of gamma-radiation: a source of gamma-radiation was wrapped in a thin lead foil, . and photoelectrons, . knocked out of the lead gamma radiation, . recorded electron spectrometer,
. It also occurred to replace the source of gamma-radiation X-ray tube and extract photoelectrons from conventional materials in order to get more information about the energies, the bonding electrons and atoms. This information was needed with. for its research on nuclear physics, to establish a correspondence between the measurements of the electron energy generated by internal conversion of gamma radiation, and nuclear transitions, generated by gamma radiation. Friends (in the scientific literature) that has been done in this area before it, with. realized that he could make a significant contribution to atomic physics, using its high-definition devices and their experience of using electronic spectroscopy.
Application of electron spectroscopy in atomic physics encounters great difficulties. Electron energy is much smaller than the energy of beta rays, and energy spectra of electrons ejected by photons, do not allow simple and clearly defined energy levels of electrons and energy relations, which describe the atomic structure. For example, Einstein showed that energy absorbed photon equals the binding energy of the emitted electron only, provided that the electron has zero velocity. In general, the photon energy is equal to the amount of energy needed to break the link, and the kinetic energy, which has an electron leaving the atom. Since the emitted electrons move with velocities that form a continuous spectrum, the spectra have the form of continuous curves, and not a series of lines.
It was known that the atomic electrons are grouped in a shell with. knew that the binding energy can be calculated easily, as he has formulated, with the help of 'measurement of the high-smeared electron cloud for various distributions of electrons associated with the membranes. However, the resolution electron spectroscopy for atomic physics would have to be 10 ... 100 times higher than in the case of radioactivity.
By the mid 50-ies. S. and his staff managed to get a clear spectral lines. In 1957, overcoming a number of other difficulties, after repeated checks of equipment with. and his two employees managed to get the first photoelectron spectrum with an unusually clean lines and expected intensities. Among other discoveries, they found the chemical shifts for the first time - slight changes in binding energies due to coupling of atoms in molecules, when their outer electrons in different ways mixed. The chemical shift reveals the details of chemical bonding, including ionic (when electrically neutral atoms acquire or donate electrons).
Proposal C. and his collaborators shape analysis with extremely high resolution, known as electron spectroscopy chemical analysis (ESHA), quickly became a permanent laboratory method. Specifically, . ESHA has been particularly useful for the study of surfaces and has found application in the study of surface phenomena, . as catalysis on platinum in the cleaning of oil or corrosion of metal ESHA used for the analysis of particles in polluted air.,
. In 1981
. S. was awarded (one half) of the Nobel Prize in Physics "for his contribution to the development of high-resolution electron spectroscopy". (His father. Manne Siegbahn was awarded the Nobel Prize for 1924. for his contribution to the development of X-ray spectroscopy). The other half of the prize was awarded to Nicholas Bloembergen and Arthur L. Schawlow for spectroscopic studies with lasers. 'With the advent of electron microscopy it became possible to determine the energy of atomic electrons with an accuracy, . far surpassing all previous opportunities, . said at the presentation of the winner Ingvar Lindgren, . Member of the Royal Swedish Academy of Sciences - is of great significance for testing nuclear models and schemes of calculations'.,
. After receiving the Nobel Prize with
. continued research in the field of nuclear physics in Uppsala. He was president of the International Union of Pure and Applied Physics and a member of the International Committee of Weights and Measures.
In 1944, Mr.. S. married Anna Brito Redin. In the couple has three sons, two of whom went in the footsteps of his father and grandfather and become physicists.
With. awarded Sixten Heyman Gothenburg University (1971) and Charles Frederick Chandler medal of Columbia University (1976). He is a member of the Swedish Academy of Sciences. Swedish Academy of Engineering Sciences. Royal Academy of Arts and Sciences at Uppsala, the Royal Norwegian Academy of Science, the Norwegian Society of Sciences and Belles Lettres, an honorary member of the American Academy of Arts and Sciences. He has an honorary degree from Durham University, Basel and Liege, as well as many scientific societies.


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