Question

Why don't heavy nuclei decay by emitting a single proton or a single neutron?

Answer 1

In most heavy nuclei, a single proton or neutron is tightly bound, so removing one requires energy. Emitting an alpha particle is often more favourable: it reduces the nucleus’s proton number and produces a more stable daughter nucleus. Single-nucleon emission can occur in certain unstable nuclei, but it is not the usual decay mode of heavy nuclei.