Lõhustumisahel

Lõhustumisahel, also known as a fission chain reaction, is a self-sustaining nuclear reaction where one nuclear fission event triggers subsequent fission events. This process typically involves heavy atomic nuclei, such as uranium-235 or plutonium-239, which are capable of undergoing fission when struck by a neutron. When a fissile nucleus absorbs a neutron, it becomes unstable and splits into two or more lighter nuclei, releasing a significant amount of energy and several additional neutrons. These newly released neutrons can then go on to strike other fissile nuclei, initiating further fission events.

For a chain reaction to be sustained, on average, at least one neutron from each fission event must cause another fission event. This is known as achieving criticality. If fewer than one neutron per fission causes another fission, the reaction will die out (subcritical). If more than one neutron per fission causes another fission, the reaction will accelerate exponentially (supercritical). The rate of the chain reaction can be controlled by adjusting the number of neutrons available to cause fission. This is achieved using control rods made of neutron-absorbing materials, which can be inserted or withdrawn from the reactor core.

Nuclear reactors utilize controlled chain reactions to generate heat, which is then used to produce electricity. Uncontrolled chain reactions, on the other hand, release a massive amount of energy very rapidly, forming the basis of nuclear weapons. The concept of the chain reaction was first theorized by Leo Szilard and later experimentally demonstrated by Enrico Fermi and his team in 1942. Understanding and controlling lõhustumisahel is fundamental to both nuclear energy production and nuclear weapons technology.