Splitting a nucleus
Fission changes nuclear structure rather than merely breaking chemical bonds. A heavy nucleus divides into lighter products, often accompanied by neutrons and radiation. Product combinations vary. Some nuclides fission spontaneously, while other reactions are induced by incoming particles, so not every event has the same trigger.
Where released energy appears
Changes in nuclear binding produce a difference between initial and final rest-mass totals. Released energy appears in moving products, radiation and subsequent interactions with surrounding matter. Nuclear energy therefore follows energy conservation; it does not provide an exception to physical energy accounting.
References: [2]
When reactions continue
Neutrons released by one fission may initiate further fissions. They may also escape or be absorbed without continuing the chain. Sustained reaction depends on the overall neutron balance. An individual nuclear event, a continuing reaction and the equipment that converts heat are distinct levels of description.
Identifying the process experimentally
Unexpected chemical products in neutron-bombardment experiments led to recognition of fission. Hahn and Strassmann’s analyses and Meitner and Frisch’s physical interpretation played complementary roles. Understanding the process required chemical separation, particle observations and nuclear models, rather than assuming that irradiation alone identified a particular reaction.
References: [2]