Nuclear fission Bohr theory

In 1938 Niels Bohr had brought the astounding news from Europe that the radiochemists Otto Hahn and Fritz Strassmann in Berlin had conclusively demonstrated that one of the products of the bom-bardmeiit of uranium by neutrons was barium, with atomic number 56, in the middle of the periodic table of elements. He also announced that in Stockholm Lise Meitner and her nephew Otto Frisch had proposed a theory to explain what they called nuclear fission, the splitting of a uranium nucleus under neutron bombardment into two pieces, each with a mass roughly equal to half the mass of the uranium nucleus. The products of Fermi s neutron bombardment of uranium back in Rome had therefore not been transuranic elements, but radioactive isotopes of known elements from the middle of the periodic table. 

Niels Bohr was a physicist, not a chemist. I devote a chapter to his life because he was the scientist who explained why Mendeleev s periodic table had the properties it did. Widely known as a soccer player in his youth, Bohr became the most influential physicist of the first half of the twentieth century. His life, too, was touched by political events. A Jew living in occupied Denmark, Bohr had to flee the country to avoid arrest by the Nazis. In 1939 Bohr discovered a theory that explained nuclear fission, and suggested that uranium 235 could be used to make a bomb. Though he played only a minor role in the American atomic bomb project, Bohr was the first to ponder the political implications of the bomb. 

Immediately after the discovery of fission (Hahn and Strassmann 1939), Meitner and Frisch (1939) gave a quantitative explanation of the process using the picture of the LDM. Bohr and Wheeler (1939) developed this picture into their classical theory, which remained the basis for the description of the nuclear fission process for many years to come. 

Bohr, Niels Hendrik David (1885-1962) Danish physicist. Niels Bohr was responsible for a key development in our understanding of atomic structure when he showed (1913) how the structure of the atom could be explained by imposing quantum conditions on the orbits of electrons, thus allowing only certain orbits. This theory accounted for details of the hydrogen spectrum. Bohr also contributed to nuclear physics, particularly the theory of nuclear fission. He was awarded the 1922 Nobel Prize for physics for his work on atomic theory. 

American scientists became active participants in attempts to confirm and extend Hahn s and Strassmann s results, which dominated nuclear physics in 1939. Bohr and John A. Wheeler advanced the theory of fission in important theoretical work done at Princeton University, while Fermi and Salard collaborated with Walter H. Zinn and... 

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