The World of Atom (Part XV)

Reference: A Logical Approach to Theoretical Physics



Chapter 89: Nuclear Theory (Werner K. Heisenberg 1901 – 1976)

The Normal States of Atomic Nuclei. Many properties of the nucleus can be discussed and understood without making specific assumptions about nucleons. The binding energy per nucleon remains the same as we go to heavier nuclei; that means nucleons inside the nucleus interact only with their nearest neighbors. The volume of the nucleus is proportional to the number of nucleons; that means nucleons are spread out uniformly throughout the nucleus.

Chapter 90: Energy Production in Stars (Hans A. Bethe 1906 – 2005)

Energy Production in Stars. Bethe set forth the law: As long as the neutron and the proton are separated by more than a critical distance (of the order of 10-13 cm) they have no influence on each other; if they are closer, there is a constant but very large pull between them. His work led to the discovery of the nuclear reactions that generate the radiation of stars. Bethe’s pioneering work with the proton-proton chain and the carbon cycle laid the foundation for the great advances that have occurred in our knowledge of the structure and the evolution of stars.

Chapter 91: Fission (Lise Meitner 1878 – 1968, Otto R. Frisch 1904 – 1968, Niels Bohr 1885 – 1962)

Disintegration of Uranium by Neutrons. The more neutrons we add to the nucleus, the more protons we must add. The bottom gets filled up with 2 protons and 2 neutrons. As more protons and neutrons are added they get stacked up getting closer to the “top of the crater.” Thus, a great deal more energy can be obtained from a fission process than is supplied to the nucleus to induce the fission. Lise Meitner and O. R. Frisch used the liquid-drop model of Bohr to point out how a splitting of uranium can occur under the appropriate conditions. They were among the first to analyze the experimental data correctly and originate the idea of nuclear fission in 1939. 

Chapter 92: Chain-Reacting Pile (Enrico Fermi 1901 – 1954)

Experimental Production of a Divergent Chain Reaction. The first chain reaction was obtained on December 2, 1942 with a “pile” constructed and successfully operated at the University of Chicago. Fermi and his co-workers achieved this by clever geometry and a proper distribution of the uranium atoms relative to carbon atoms. To produce a chain reaction or a self-sustaining pile a game of slowing down and catching neutrons must be played. Fermi showed that a chain reaction is possible only if at least 1.22 of the original 2 neutrons become thermal neutrons and give rise to fission.

Chapter 93: Power from Fusion (Ernest W. Titterton 1914 – 1990)

Power from Fusion? Long lasting radioactive byproducts from fission process make it an untenable power source. The possibility of producing power without such hazard exists through the use of nuclear fusion. This is the natural process of “thermonuclear” reactions occurring in our sun and all the stars. Unfortunately, to produce fusion artificially is a difficult task. An account of the way in which fusion comes about and how this process proceeds naturally in the stars is lucidly explained in E. W. Titterton’s book ‘Facing the Atomic Future’.


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