How can gamma rays or energetic particles induce nuclear fission?

Nuclear fission can be induced by exciting a nucleus to an energy level equal to or greater than its fission barrier, the threshold energy required for the nucleus to split. When a nucleus receives sufficient excitation energy, it may distort from its stable shape into a dumbbell configuration and subsequently divide into two nearly equal fragments.12

This excitation can be achieved through two primary methods:

• Particle-induced fission: A nucleus can be excited by the capture of a neutron, proton, or other subatomic particles. The binding energy released upon the capture of a particle—particularly a neutron—often provides the necessary energy to surmount the fission barrier. For some isotopes, the binding energy alone is sufficient, while others require the additional kinetic energy of an incident particle to trigger the process.1
• Gamma-ray excitation: Known as photofission, this process occurs when a nucleus absorbs high-energy gamma-ray photons. This absorption distributes energy among the nucleus's degrees of freedom, potentially leading to fission.134