In 1938, the Italian physicist Enrico Fermi, who had fled to New York to escape fascism, he discovered a material in which a process of this type occurred: uranium. Fearing that the Nazis can also discover the ability of this element of producing a chain reaction, the Manhattan project A secret program for the development of nuclear weapons led by Arthur Compton was born in 1940. Compton formed a research group, which also included Fermi and Szilard, who would continue to conduct experiments on the reactions of the nuclear chain. The theoretical physicist Julius Robert Oppenheimer was also part of the team.
On December 2, 1942, the first real experiment took place under the football field of the University of Chicago; In a squash field, physicists built a nicknamed reactor “Chicago 1 batteries” This reached the first nuclear reaction never supported by man, providing confirmation of the idea of Szilard. In 1943, Oppenheimer became project manager at the Los Alamos Laboratories in New Mexico, where the first real nuclear device in history would have been designed and built. On July 16, 1945, the United States made him explode in the New Mexico desert. Twenty days later, on August 6, a similar bomb fell into the Japanese city of Hiroshima and on August 9 in the city of Nagasaki, leading to Japan’s surrender several days later and at the end of the Second World War.
A matter of nuclei
As we all learn at school, the atoms are composed of a nucleus of neutrons and protons, around which electrons orbit. Atomic nuclei can join to form larger atoms or fragments to form smaller atoms. The first case is called nuclear fusion and is the process that occurs in the stars and that today the researchers are trying to recreate in the laboratory as a means of producing energy. Under infernal heat and pressure, the atoms merge to form heavier atoms. For example, in a star like the sun, hydrogen nuclei merge to form helium nuclei. This process releases energy, which radiates into the sun system, creating livable conditions on earth.
When a core is divided, however, we call it nuclear fission, which we use in a controlled way in nuclear power plants and deliberately uncontrolled in nuclear bombs. In this case, the most unstable atoms heavier are fragmented in lighter atoms, a process that also releases energy. In addition to energy, excess neutron neutron are also released, triggering exactly the fission chain reaction conceived by Szilard. To support a chain reaction, however, the fissile material must reach criticality, a state in which fairly neutrons are released and hit other atoms to continue to trigger further atoms. In a nuclear reactor, reaching criticality is the goal; In an atomic bomb, it must be overcome, in which a reaction triggers multiple reactions and causes the increase in the process.
From fission to merger
Those weapons discussed so far are “classic” atomic bombs, based on fission. Generally, an atomic bomb is triggered by a chemical explosion, which compresses a mass of uranium or plutonium until it exceeds criticality. Subsequent developments in this field of research, however, led to another type of nuclear device, called the melting bomb. These are called thermonuclear bombs, in which a sequence of two explosions occurs. The primary explosion is equivalent to a fission bomb, with the aforementioned sequence of chemical explosion and fission chain. The energy issued by the primary explosion therefore leads to a secondary explosion, used to trigger the merger of hydrogen atoms. The most powerful device of this type ever designed and tested is Tsar’s famous bomb, which was detonated in the Arctic in 1961 by the Soviet Union.
How the explosion occurs
We all have the image of a cloud of mushrooms in our minds. But how does it originate? As soon as a atomic bomb explodes, within the first second, there is a sudden release of energy in the form of free neutrons and gamma rays. The explosion appears as a fiery sphere that expands up to tens of kilometers from the trigger. This fiery explosion, which rises in the atmosphere, creates the typical form of mushrooms. A thermal flash occurs; The heat emitted can start fires and cause burns to kilometers from the center of the explosion (depending on the power of the bomb).
Expanding thus quickly, the explosion creates a shock wave, a sudden change in the atmospheric pressure that creates much of the destruction associated with atomic bombs. The peculiarity of atomic bombs, however, is the radioactive relapse: a shower of fission products that spreads on the area surrounding the explosion and that can contact it with radioactive elements for decades.
This story originally appeared on Wired Italy And it was translated by Italian.