Alpha-Crystal: A Simple Model for Nuclear Structure

When nuclear structure models were first derived in the 1930s, it was believed that nucleons were elementary particles similar to electrons, so that a nucleus should be analogous to an atom. For this reason, a shell model analogous to atomic orbitals was proposed for the nucleus. But since the 1970s, it has been understood that nucleons are composed of quarks, and are therefore analogous to atoms, so that a nucleus is more analogous to an atomic cluster. With that in mind, a new simple conceptual picture of the nucleus is proposed, which is suitable for instruction to undergraduates. Given the great stability of alpha particles, and the observation of alpha emission from radioactive nuclei, it is natural to propose that a large nucleus is composed primarily of alphas. I suggest a close-packed “crystal” of alphas, with at most one “partial alpha” at the outer surface. Furthermore, given the strong electric potential in the center, the alphas in the center may convert to 4 neutrons, forming a “neutron core” providing excess neutrons for large nuclei. One can further approximate such a structure with spherical charge distributions, and derive simple analytical equations for the excess neutrons and the binding energy per nucleon, similar to those observed. Such a simple model may also offer insights into nuclear stability, fission, and other nuclear phenomena.