Preformation Factor in Emission of Complex Particles from Nuclear Reactions

The reason why complex particles (alphas, tritons, ${\mathrm{Li}}^6$ nuclei, etc.) are emitted in nuclear reactions as frequently as nucleons (after corrections for Coulomb barrier penetration and energetics), whereas ice crystals are never emitted from evaporating water droplets is investigated. It is shown that the difference is entirely explained by the fact that a nucleus is a highly degenerate system subject to Fermi-Dirac statistics, whereas an evaporating water droplet is a nondegenerate statistical system.