What causes an atomic bomb to explode?

Answer 1

The basic principle of an atomic bomb is that of nuclear fission. Fissile material is matter that is radioactively decomposing into another type of matter, with the nucleus of each atom in the material releasing energy in the form of free neutrons and photons, thus becoming a different, lighter nucleus/atom. With a great enough mass or density of fissile material in one place, there is a greatly increased chance that the freed neutron of one nucleus will impact with the nucleus of another atom and trigger its fission. Beyond a critical point (known as the 'critical mass' of the fissile material), this becomes a runaway cascade of nuclear fissions releasing vast amounts of energy in an incredibly short amount of time.

A nuclear bomb is designed to carry fissile material to a target before triggering a mechanism that will allow that material to achieve critical mass. One way of doing this is to carry two pieces of sub-critical mass, then fire one violently into the other to generate a single critical mass. The more practical way (for reasons of weight, safety, and reliability) is to have one critical mass shaped to mitigate the possibility of a chain reaction, then trigger shaped charges surrounding the mass which serve, through a confluence of explosive shock waves, to compress the mass to a critical density, triggering the chain reaction.

The net release of energy produces a phenomenally destructive explosion of heat, light, and harmful radiation.

Answer 2

An atomic bomb explodes due to a chain reaction of nuclear fission. When the bomb is detonated, a neutron initiates the fission process, splitting atoms in the bomb's core and releasing immense amounts of energy. This energy release results in an explosive blast.