A heavy nucleus splits into lighter nuclei releasing large energy, as in nuclear reactors.
Practise Atomic Structure & Periodicity All Atomic Structure & Periodicity topics
In nuclear fission a heavy nucleus, such as uranium-235, absorbs a neutron and splits into two lighter nuclei, releasing two or three neutrons and about 200 MeV of energy. The released neutrons can trigger further fissions, producing a chain reaction. In nuclear reactors the chain reaction is controlled with control rods and a moderator, while in a bomb it is uncontrolled. Fission is the basis of nuclear power generation. The energy comes from the increase in binding energy per nucleon when the heavy nucleus splits.
Key ideas: A heavy nucleus splits after neutron capture into two mid-sized nuclei plus 2 to 3 neutrons, releasing about 200 MeV per event: 235U + n gives 141Ba + 92Kr + 3 n. Chain reaction needs critical mass, with moderators (water, graphite) slowing neutrons and control rods (B, Cd) absorbing them. 1 kg of 235U gives about 8 x 10^13 J.
Common mistakes and connections: Students think reactors can explode like bombs; reactor fuel is only 3 to 5 percent 235U, while weapons need above 90 percent. Another error is thinking the products are stable; they are radioactive waste. Fission yields energy because binding energy per nucleon rises for mid-mass nuclei. It contrasts with fusion.
Splitting one uranium-235 nucleus releases about 200 MeV, mostly as kinetic energy of the two fission fragments that heats the reactor. The interactive lesson shows this as a live animation or chart.
A U-235 nucleus absorbs a neutron and splits into barium-141 and krypton-92, releasing three neutrons.
A heavy nucleus splits into lighter nuclei releasing large energy, as in nuclear reactors.
Nuclear Fission is a intermediate topic in Atomic Structure & Periodicity. It builds on the vocabulary of beginner topics in this area.
Study these earlier topics in Atomic Structure & Periodicity first: Beta Decay, Gamma Radiation, Half-life.
The next topics in Atomic Structure & Periodicity are Nuclear Fusion and Radiocarbon Dating.
Yes. The interactive lesson includes a self-check question on Nuclear Fission, and the Atomic Structure & Periodicity quiz draws on every topic in this area.
Nuclear Fission is topic 108 of 115 in Atomic Structure & Periodicity.