JENSEN (Jensen), Johannes Hans D.

June 25, 1907, Mr.. - 11 February 1973
German physicist Johannes Hans Daniel Jensen was born in Hamburg in the family gardener Carl Jensen and Helen nee Ohm. The brilliant successes of the young J. the school allowed him to get a scholarship to the Oberrealshulle (High Real School) in Hamburg. After graduation in 1926, Mr.. He went on to study physics, mathematics, physical chemistry and philosophy at the universities of Freiburg and Hamburg. After receiving his doctorate in physics from the University of Hamburg (1932), J. was left there to work as an assistant researcher. In 1936, Mr.. He obtained a doctorate in physics and in 1937. worked as a privat-docent. In 1941, Mr.. J. became professor of Theoretical Physics, Technical University of Hanover, and from 1949. - Professor of Physics at the University of Heidelberg, where in 1955. appointed dean of the Faculty of Physics. In 1969. He was honored a title of honorary professor.
The first job J. was devoted to the theory of materials (quantum-mechanical emission of ionic lattices, the systematic arrangement of atoms in crystals) and their properties at high pressures. Investigation of ionic lattices led J. in 1947. to address the problem of distribution efficiency in the emission of radiation by nuclei of atoms in molecules and crystals. The emission of 'tied' to the lattice of atoms of radioactive solid particles or photons atoms experiencing the impact, ie. move in the opposite direction, like a gun after the shot. The value of these works J. was appreciated only in 1958 when Rudolf L. MцІssbauer discovered the phenomenon of emission of gamma radiation without recoil. Gamma radiation kills all the energy of nuclear transition, so the transition becomes very clearly definable (Mossbauer effect).
From the very beginning of his scientific career ц?. closely followed the evolution of ideas about the core. With the discovery in 1932. neutron English physicist James Chadwick proved, . that the nucleus consists of protons (solid particles with a single positive electrical charge) and neutrons (particles with mass, . almost identical with the mass of the proton, . without electric charge),
. To explain the behavior of the core was proposed many models of nuclear structure of protons and neutrons. The first observations showed that nuclei with certain numbers, Eugene P. Wigner called them magical, an unusually stable (ie. the probability of their transition to other nuclei with the emission of a radiation or by nuclear reactions is very small) and relatively widely distributed in nature. Stability and prevalence of interrelated, since stable kernel do not break down and have a tendency to accumulate. In 1933. German physicist Walter Elsasser proposed a model whereby the protons and neutrons in some way involved in the orbital motion and orbit, as required by quantum theory, correspond to discrete energy. In addition to the core of the new proton or neutron number of orbits increases. Energy orbits are separated from each other at the same values, and 'going' in the group, or shell, separated by relatively wide energy gaps. When added to a proton or neutron occupy the last of the 'approved' energy levels, it is believed that the shell is closed and the nucleus is particularly stable. Snatch nucleon (the collective name of a proton and a neutron) with a hard shell, and the addition of a new nucleon requires relatively high energy, as it should 'go up' before the next shell. Elsasser model allowed to describe a few light nuclei. But it proved insufficient to describe heavier nuclei or nuclei, are in highly excited states.
. Thinking in terms of nuclear shells physicists were accustomed to and more comfortable because of the similar situation in the atom as a whole, with the electrons orbiting the nucleus
. (A revised version of quantum theory rejects the attractively simple picture, . once proposed by Niels Bohr, . - Model, . in which electrons are treated at various discrete distances from the nucleus, . but the model is still useful.) electron energy, . appropriate to their situation and state of motion, . quantized, . ie,
. can take only certain discrete values (belong to a certain energy levels). In particular, the energy values correspond to the angular momentum of electrons on their orbital motion. Quantum theory (which confirm the prediction experiments) in correspondence with each allowed value of angular momentum a certain number of energy levels. In addition, the electrons rotate around its axis like spinning tops. Since the movement of electrons creates an electrical current, a magnetic field. Just like two magnets attract or repel each other, angular momentum and spin of electrons interact (spin-orbit coupling), trying to line up in one direction. As a result, there are additional energy levels.
. Atomic energy levels naturally grouped in shell, . separated by relatively large energy gaps between the electrons, . filling the upper level of the lower shell, . and electrons, . filling the lower levels following, . higher shell,
. A closed envelope indicates stability. In this case the chemical stability, as well as the chemical reactions associated with the loss, seizure or socialization of the electrons. Shell model explains the periodic system, in which the chemical elements arranged by atomic number and grouped by similarity of their chemical properties. The periodic table shows that the chemical properties of cyclically or periodically repeated with increasing atomic number. In some rooms atoms are particularly stable. Such, for example, the numbers of elements, known as the 'noble' gases, which include helium, neon, argon, xenon and radon (they are almost chemically inert). The periodic repetition of chemical properties associated with the filling of shells and the beginning of the next shells, naturally follows from the principles of quantum physics, applied to the electronic energy levels.
Interest J. to analyze the structure of the shells in the nucleus has increased even more when geochemist, Hans E. Suess and a specialist in experimental nuclear physics Otto Haksel asked him to consider some of the characteristic patterns observed by them in such distant areas as nuclear physics and geochemistry. Suess drew attention to the unusual prevalence of certain elements and their isotopes (nuclei of atoms with one and the same number of protons but different numbers of neutrons). His observations, he said Hakselyu, who discovered in the same isotopes unusual nuclear properties. In nuclei with a magic number of protons or neutrons, the prevalence and stability coincided. However J. not know what to include in its theoretical framework the notion of the magic number, and was not convinced of its importance.
Beginning of the Second World War halted the study ц?. and, in his words, 'the physicists plunged Germany into a state of suffocating isolation'. Only a few years after the war he was able to resume discussions in Copenhagen with Niels Bohr, whom he treated with great respect.
In Copenhagen, TH. read an article by Maria Goeppert-Mayer, 'On the closed shells in nuclei' ( 'On Closed Shells in Nuclei'), which included a review of all existing empirical data collected by the author in the search for the interpretation of magic numbers. interest has been neglected topics. Among his models was considered by the model of the nucleus, which consists of moving along the orbits of protons and neutrons with a strong spin-orbit coupling. Such representation contrary to the then dominant views of leading physicists, who considered it unlikely to exist in the nucleus of strong spin-orbit coupling. As noted later J., 'Fortunately, I was not too well educated, was not familiar with these views and did not remember particularly hard on the old objections to the strong spin-orbit coupling'. Despite initial successes in the study of higher magic numbers, J. are uncertain because of his differences with the conventional wisdom and was not surprised when the journal rejected it serious note of the results, citing refusal by saying that 'this is not physics, but a game of numbers'.
. Discussions with Bohr and other scientists have allowed J
. gain confidence and develop his theory of nuclear energy levels associated with the orbital angular momenta and the influence of the nuclear spin, as well as to explain the existence of all seven known magic numbers: 2, 8,20,28, 50, 82.126. Scheme J. somewhat reminiscent of a similar scheme for the atomic electrons, but required changes due to differences between the nucleus and the atom as a whole. For example, the electrons are relatively far from the nucleus and from each other (the atom is mostly empty space), while the nucleons are tightly packed. At the electrons are well-known electrical power. Their action is manifested at large distances. The forces of interaction between the nucleons scientists in the 50-ies. seemed more mysterious: they manifested only at very short distances, and about a million times superior to the intensity of electrical forces. Electrons moving in a force field, which obviously had a center of attraction in a positively charged nucleus. Inside the nucleus of such an explicit center was not.
When J. in 1949. sent an article on the theory of nuclear shells for publication in 'Physical review' ( 'Physical Review'), it became known that the Goeppert-Mayer came to similar conclusions, and sent his article in the same journal. Both were published in two editions of his. Subsequently J. and Goeppert-Mayer met in Germany, became friends and in 1955. together wrote a book 'The elementary theory of nuclear shell structure' ( 'Elementary Treory of Nuclear Shell Structure'). Their theory made it possible to explain the excitation of nuclei in collisions with massive particles and gamma-rays, . predict a low probability of neutron capture so-called magic nuclei and the existence of numerous isomers for nuclei with large angular momentum,
. Isomers, called the kernel, having the same number of protons and neutrons, but different state of excitation and the rate of radioactive decay. Assumptions J. Goeppert-Mayer and were subsequently confirmed experimentally.
And. and Maria Goeppert-Mayer was awarded half the Nobel Prize in Physics 1963. 'for the discovery of the shell structure of the nucleus'. The second half of the prize was awarded to Eugene P. Wigner. Introducing the winners, Ivar Waller of the Royal Swedish Academy of Sciences noted that the opening of the Goeppert-Mayer, and J. 'shed new light on the structure of atomic nuclei' and are 'the most impressive success in establishing the correlation between the properties of nuclei'.
In his Nobel lecture J. described the isolation of German physicists during the war, about his discussions with Hakselem and Suess, on the interpretation of magic numbers and the article Goeppert-Mayer, which he happened to read after the war,. Conclusions Meyer, J. said, prompted him to meet with Bohr, and 'since then I began to seriously consider the possibility of' demagizatsii 'magic numbers'.
In addition to the work for which he was awarded the Nobel Prize, TH. conducted research on the so-called giant resonance in the nuclear photoeffect. In 1955, Mr.. He suggested the so-called gamma-invariance of weak interaction (weak force associated with radioactivity, strong - hold the nucleons in the nucleus). This property is related to violations of conservation of parity - the rule that obeys the conservation of some symmetry in nuclear transitions. Chen Ning Yang and Lee Tszundao theoretically demonstrated the possibility of parity violation, a method of experimental verification of the weak interaction of parity conservation, for which he was awarded the Nobel Prize in Physics in 1957
J. visited as a visiting professor of physics at the University of Wisconsin (1951), . Princeton Institute for Basic Research (1952), . University of California at Berkeley (1952), . Indiana University (1953), . University of Minnesota (1956) and the University of California at La Jolly (1961),
. Modest and reserved man, J., remained a lifelong bachelor, he lived in an apartment located above the Institute of Theoretical Physics in Heidelberg
. In his spare time he liked to tinker in the garden of the institute, bred turtles. Since 1955. until his death, February 11, 1973, he was co-editor 'Journal of Physics' ( 'Zeitschrift fur Physik').
J. was a member of the Heidelberg Academy of Sciences, the Max Planck Society and an honorary doctor of Hannover Technical University.