Atomic bomb


August 19, 2022

The atomic bomb (also called "A bomb" according to an obsolete terminology, or sometimes referred to by the improper name "nuclear bomb") is the name by which the nuclear fission bomb is commonly indicated. It is an explosive device belonging to the nuclear weapons group, whose energy is entirely produced by a nuclear fission chain reaction. The term is also commonly used to indicate thermonuclear weapons, as they make up the majority of nuclear arsenals today. The operation of these devices is based on the nuclear fission reaction, a process of dividing the atomic nucleus, which takes place in a heavy element called fissile, into two or more nuclei of lower mass, following the collision with a free neutron. The rupture of the nucleus in turn produces, in addition to lighter elements, also some additional free neutrons, as well as a very significant amount of energy. If the fissile material has a sufficient degree of concentration and is in a sufficiently large mass, called "critical mass", the free neutrons produced in turn are able to hit new nuclei of the fissile element, producing an uncontrolled chain reaction that propagates throughout the mass of material releasing an immense amount of energy in a very short time. The atomic bomb is a weapon of mass destruction, the production of which the international community limits and sanctions under the Nuclear Non-Proliferation Treaty (NPT).


The theoretical foundation is the principle of mass-energy equivalence, expressed by the equation E mc² foreseen in Albert Einstein's special theory of relativity. This generic equivalence suggests in principle the possibility of directly transforming matter into energy or vice versa. Einstein saw no practical application of this discovery. He understood, however, that the principle of mass-energy equivalence could explain the phenomenon of radioactivity, that is, that certain elements emit spontaneous energy. Subsequently, the hypothesis was advanced that some reactions based on this principle could actually take place inside atomic nuclei. The "decay" of the nuclei causes a release of energy. The idea that a nuclear reaction could also be produced artificially and massively, in the form of a chain reaction, was developed in the second half of the 1930s, following the discovery of the neutron. Some of the major research in this field was conducted in Italy by Enrico Fermi. A group of European scientists who took refuge in the United States (Enrico Fermi, Leó Szilárd, Edward Teller and Eugene Wigner) worried about the possible military development of the principle. In 1939 the scientists Fermi and Szilard, based on their theoretical studies, persuaded Einstein to write a letter to President Roosevelt to signal that there was a hypothetical possibility of building a bomb using the fission principle and it was likely that the German government had already arranged research on the subject. The US government thus began to take an interest in research. Enrico Fermi continued in the United States new research on the properties of a rare isotope of uranium, uranium-235, until he obtained the first artificial self-powered chain fission reaction: on 2 December 1942 the group headed by Fermi assembled the the first "atomic pile" or "nuclear fission reactor" that reached the critical condition, consisting of a mass of natural uranium and graphite arranged heterogeneously. A few months earlier, in June 1942, based on calculations made in a summer physics session at the University of California led by Robert Oppenheimer, it was concluded that it was theoretically possible to build a bomb that exploited the fission chain reaction. . Its technical realization r