The Birth of the Bohr Model

We follow Niels Bohr from his 1911 dissertation on the electron theory of metals to his 1913 trilogy on the constitution of atoms and molecules. The dissertation shows that Bohr was thoroughly familiar with the early work of predominantly German physicists on quantum theory and that he suspected that the behavior of bound rather than free electrons called for new laws of physics. During postdoctoral work with Rutherford in Manchester, Bohr learned about the alpha-scattering experiments by Geiger and Marsden that led Rutherford to suggest that an atom consists of a nucleus containing most of its mass with a cloud of electrons swirling around it. Bohr tried to infer the atomic structure in more detail from these and further alpha-scattering experiments. Bohr’s models are in the tradition of British atomic modeling of J.J. Thomson and others but Bohr also borrowed from Planck the notion that energy is proportional to frequency. These early ideas have been preserved in the so-called Manchester memorandum, a set of notes Bohr prepared for Rutherford before returning to Copenhagen in July 1912. In this memorandum, Bohr only considered the ground state of an atom and focused on chemical rather than spectroscopic phenomena. He first started thinking about excited states when he encountered models similar to his own by another British model builder, Nicholson. His interest shifted from chemistry to spectroscopy when a Danish colleague, Hansen, alerted him to the Balmer formula. Within a month of first laying eyes on Balmer’s formula, Bohr submitted the first installment of his trilogy, which contains his famous model of the hydrogen atom. In the following months he completed the trilogy, dealing with more complicated atoms and molecules and presenting results directly coming out of the research recorded in the Manchester memorandum.

Stability of $\alpha$-chain states against disintegrations

We focus on the raison d’être of the $\alpha$-chain states on the basis of the fully microscopic framework, where the Pauli principle among all the nucleons is fully taken into account. Our purpose is to find the limiting number of $\alpha$ clusters on which the linear $\alpha$-cluster state can stably exist. How many $\alpha$ clusters can stably make an $\alpha$-chain state? We examine the properties of equally separated $\alpha$ clusters on a straight line and compare its stability with that on a circle. We also confirm its stability in terms of binary and ternary disintegrations including $\alpha$-decay and fission modes. For the effective nucleon–nucleon interaction we employ the F1 force, which has finite-range three-body terms and guarantees overall saturation properties of nuclei. This interaction also gives a reasonable binding energy and size of the $\alpha$ particle, and the $\alpha$–$\alpha$ scattering phase shift. The result astonishes us because we can point out the possible existence of $\alpha$-chain states with vast numbers of $\alpha$ clusters.