How does nuclear bomb work?

In decades after the Second World War, nuclear bombs represented a growing threat to human civilisation. Almost all of us are aware of their destructive power, despite being used only twice in combat, but not many people know why this is and how they work. That is what we will try to explain in this article.

Atom

It is known that all matter is made out of atoms, and atoms themselves out of three different kinds of subatomic particles - protons (with positive electrical charge), neutrons (with neutral charge), and electrons (negatively charged). Protons and neutrons are situated together in the centre of an atom - nucleus, while electrons surround them forming a so-called "electron cloud". Radiation, which is one of the main components of a nuclear explosion, is a consequence of various processes in the atom.

Atom structure. Credits: Wikipedia

Fission and fusion

Processes which emit radiation are fission and fusion.
Fission is achieved by shooting a neutron into a heavy atom, which becomes unstable and splits into two smaller atoms. It also releases electromagnetic radiation and a couple of neutrons, that start a chain reaction upon hitting newly formed atoms. The most commonly used elements for fission are Uranium-235 and Plutonium-239 because they are the easiest to initiate and control.

Fission. Credits: Wikipedia

Fusion is a reversed process to fission - two light atoms are collided, forming a heavier one, thereby releasing massive amounts of energy. Elements used for nuclear fusion are usually hydrogen isotopes deuterium and tritium since they are light and highly reactive.

Fission. Credits: Wikipedia

Bomb structure

Modern nuclear bomb, called hydrogen bomb, uses a combination of conventional explosives, fission and fusion, for the most effective detonation. When dropped, the primary stage starts. Conventional explosives in the bomb cause uranium and plutonium (in the form of a two-layer sphere) to start fission. Released heat and pressure cause the secondary stage, in which hydrogen isotopes fuse. Both stages release massive amounts of energy in the form of radiation, and temperatures in the place of detonation reach those in the centre of the Sun.

Nuclear bomb structure. Credits: Wikipedia

Nuclear detonation consequences

The worst consequence of the nuclear bomb detonation is its effect on people, due to emitted radiation. It is found in three forms: alpha, beta and gamma radiation.
Alpha radiation is made of alpha particles - helium atoms. These particles can not penetrate through clothes, so they are not able to cause serious damage to the organism.
Beta radiation is made of beta particles - electrons. These can penetrate clothes and skin, but not walls and other thicker objects, and can be used in medicine for treating tumours.
Gamma radiation is made of protons. It can penetrate through most materials and cause serious damage to living organisms, by changing DNA and causing cancer.

In 1980, during the Cold War, scientists introduced us to the possible outcome of a large-scale nuclear war - "nuclear winter". In that scenario, so many bombs would be dropped that radioactive clouds of dust would cover the atmosphere, leading to a drop in surface temperature and radioactive fallout (rain from radioactive clouds) which would poison water. These effects would certainly cause the extinction of many species, possibly including humans.