“Nuclear reactions in the continuous energy region.” Offprint from Nature, Vol. 144, pp. [200-201], July 29, 1939

1939. FIRST EDITION. In perfect condition. First edition, first printing, the rare author’s offprint issue. This is the sequel to Bohr & Kalckar’s earlier work “On the transmutation of atomic nuclei by impact of material particles” which had introduced the “liquid-drop model” of the nucleus, a description of atomic nuclei in which the nucleons (neutrons and protons) behave like the molecules in a drop of liquid. If given sufficient extra energy (as by the absorption of a neutron), the spherical nucleus may be distorted into a dumbbell shape and then split at the neck into two nearly equal fragments, releasing energy. Here the authors treat the “optical model” which describes the atomic nuclei as similar to cloudy crystal balls in that, when struck by a beam of particles, they partially absorb the beam, partially scatter it, and partially transmit it in a way analogous to the behavior of light.

“Using the optical theorem and Bohr’s liquid-drop model of the nucleus, Placzek (1905-1955), Bohr (1885-1962), and Peierls (1935-2003) offered a fundamental theory of neutron-induced nuclear reactions. These works proved essential to the subsequent development of nuclear theory and to development of nuclear reactor design” (DSB).

Although a footnote which appears at the end of the articles stating that “the details of this and of the other arguments of this note will be published in the Proceedings of the Copenhagen Academy,” no other version of this paper ever appeared.

DSB, II, pp. 239-255 (Bohr); DSB, XVIII, pp. 714-715 (Placzek).