fissioiden

Fissioiden is the Finnish term used in contexts discussing nuclear fission. Fission itself is the process by which a heavy atomic nucleus splits into lighter nuclei, accompanied by energy release and emission of neutrons. It can occur spontaneously in some isotopes or be induced by neutron absorption. When neutrons released by one fission strike other nuclei, additional fissions may occur, creating a self-sustaining chain reaction under suitable conditions. Materials that readily undergo fission with slow (thermal) neutrons, such as uranium-235 and plutonium-239, are termed fissile; others may fission only with fast neutrons or may not fission at all.

The energy yield of a fission event is about 200 MeV, distributed mainly as the kinetic energy of fission fragments, with prompt neutrons and gamma radiation contributing as well. The immediate products are fission fragments, typically radioactive and decaying through beta emission to stable isotopes; these decay chains produce fission products like iodine-131 and cesium-137 among others.

Fission is central to both civilian and military uses. In nuclear reactors, neutron moderators and control rods regulate the rate of fission to produce steady heat, which is converted to electricity. In uncontrolled settings, rapid fission can drive explosive yields. Safety concerns center on radioactive waste, long-lived fission products, and accident risk.

Historically, fission was discovered in the 1930s, with theoretical explanation by Meitner and Frisch. The first controlled chain reaction occurred in 1942 (Chicago Pile-1), marking a turning point in science and energy development.