Fissia

Meet Fissia, a uranium nucleus who splits in two when a neutron knocks.

A uranium-235 nucleus that absorbs a slow neutron becomes very unstable and can split into two smaller nuclei, releasing a few fast neutrons and a large amount of energy. Otto Hahn and Fritz Strassmann found barium among the products of neutron-bombarded uranium in 1938, and Lise Meitner and Otto Frisch explained it as splitting, naming it fission. Hahn received the 1944 Nobel Prize in Chemistry.

Each fission releases about 200 MeV. One kilogram of uranium-235 holds 1000 / 235 × 6.022 × 10²³ ≈ 2.56 × 10²⁴ nuclei, so complete fission would give about 2.56 × 10²⁴ × 200 × 1.602 × 10⁻¹³ J ≈ 8.2 × 10¹³ J, millions of times more than burning a kilogram of coal.

The released neutrons can split further nuclei. Controlled, that chain reaction runs nuclear power stations; reactors use control rods to absorb spare neutrons.

The barium-141 and krypton-92 split shown is one of many possible pairs, and the number of neutrons varies, averaging about 2.4. The fragments are radioactive, which is why spent fuel must be stored carefully.