2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/17686We report numerical calculations of the concentration of interstitials in hard-sphere crystals. We find that, in a three-dimensional fcc hard-sphere crystal at the melting point, the concentration of interstitials is 2 * 10^-8. This is some three orders of magnitude lower than the concentration of vacancies. A simple, analytical estimate yields a value that is in fair agreement with the numerical results.12 pages, 2 figures; Submitted to J. Phys. Chem. BSoft Condensed Mattertext