Radioactivity Study Guide

Nuclear fission is the process where a large, unstable atomic nucleus splits into two or more smaller nuclei, releasing a significant amount of energy. In the case of uranium-235 (U-235), fission is typically induced by the absorption of a slow-moving neutron. When a U-235 nucleus absorbs a neutron, it forms a highly unstable U-236 nucleus. This unstable nucleus immediately splits into two smaller nuclei, often referred to as 'daughter' nuclei (e.g., krypton and barium). In addition to the daughter nuclei, two or three high-energy neutrons are released during this process. Crucially, mass is converted into energy according to Einstein's mass-energy equivalence (E=mc²), resulting in a large release of kinetic energy of the fission products and electromagnetic radiation.

A controlled nuclear chain reaction is the fundamental process used in nuclear reactors to generate electrical power. It begins when a neutron strikes a large, unstable nucleus, such as Uranium-235, causing it to split in a process called nuclear fission. This fission releases energy, along with additional neutrons. These newly released neutrons can then strike other unstable nuclei, causing further fission events, thus propagating a chain reaction. To control this reaction and prevent it from escalating uncontrollably (as in a nuclear weapon), control rods, typically made of neutron-absorbing materials like boron or cadmium, are used. These rods are inserted into the reactor core to absorb excess neutrons, thereby regulating the rate of fission and the amount of energy released, maintaining a steady power output.