中子活化指将样品用中子照射后，样品中原子经中子俘获而变得具有放射性的过程。俘获中子后的原子核通常会立即衰变，释放出中子、质子或阿尔法粒子同时生成新的活化产物。这些活化产物半衰期或长或短，从几秒钟到几十年都有可能。核素钴-60就是通过中子俘获反应在核反应堆中制备

钴-60释放出电子和伽马射线衰变成镍-60，半衰期为5.27年。因为其天然同位素钴-59丰度为100%且容易获得，因此钴-60成为一种易得、有效的放射源，广泛用于放射性治疗。

某些核素俘获中子后会发生核裂变。轻元素中，只有铍-9能吸收快中子，发生这样的裂变：

Neutron activation is the process in which neutron radiation induces radioactivity in materials, and occurs when atomic nuclei capture free neutrons, becoming heavier and entering excited states. The excited nucleus often decays immediately by emitting gamma rays, or particles such as beta particles, alpha particles, fission products and neutrons (in nuclear fission). Thus, the process of neutron capture, even after any intermediate decay, often results in the formation of an unstable activation product. Such radioactive nuclei can exhibit half-lives ranging from small fractions of a second to many years.