Today, the UN reports, despite disarmament efforts and numerous international treaties, there are still 13,400 nuclear warheads in the world. Leading the way is the Russian Federation with 5,889 and the United States with 5,244. Without detracting from their cruelty, however, the physics behind nuclear devices remains both a complex and fascinating subject.
Journey from the Concept to the Atom
The year 1933 marked Adolf Hitler's ascension as chancellor, initiating the Third Reich, a Nazi state that morphed into a totalitarian regime. The same year, Hungarian scientist Leo Szilard, a Jewish refugee in the United Kingdom, struck upon an idea. He theorized that triggering a neutron to hit an atom, which then emits two or more neutrons, would result in a self-propelled chain of nuclear fission reactions. This process would release a significant amount of energy, leading to the creation of a bomb.
Dissecting the Atomic Bomb: History and Physics
In 1938, Enrico Fermi, an Italian physicist and a refugee in New York, discovered an atom that underwent the process theorized by Szilard. Fearing that the Nazis might stumble upon the chain reaction, the Manhattan Project was initiated in 1940 under the leadership of Arthur Compton, featuring key members like Fermi and Szilard. The project focused on nuclear weapons experimentation and chain reactions, with Julius Robert Oppenheimer, a theoretical physicist, as a pivotal part of the team.
On December 2, 1942, the University of Chicago football field became the backdrop for the first actual experiment validating Szilard's theory. By 1943, Oppenheimer was appointed the project manager at Los Alamos Laboratories in New Mexico, the birthplace of the world's first nuclear device. On July 16, 1945, the United States detonated it in the New Mexico desert. Merely twenty days later, on August 6, an atomic bomb devastated the Japanese city of Hiroshima, followed by Nagasaki on August 9, marking the end of World War II.
Examining Atomic Cores
Atoms comprise a nucleus of neutrons and protons with electrons orbiting around it. These atomic nuclei can either combine to form larger atoms or fragment into smaller ones. The former process is known as nuclear fusion, a phenomenon occurring in the cores of stars. Under tremendous temperature and pressure, atoms are compressed to the extent that they merge to form heavier atoms. This process liberates energy, which we perceive as light. For instance, the fusion of hydrogen nuclei in the Sun forms helium nuclei, thus illuminating our world.
Atomic bomb the history and physics
When, on the other hand, a nucleus splits, this is called nuclear fission, and it is what we exploit in a controlled way in atomic power plants and in a deliberately uncontrolled way in nuclear bombs. In this case, heavier atoms are fragmented into lighter atoms, but again the process causes the release of energy. However, in some elements, such as uranium-235 and plutonium-239, some excess neutrons are released in addition to energy, triggering precisely that chain fission reaction devised by Szilard. In order to trigger and maintain the chain reaction, however, the fissile material must reach at least a critical mass: this is the minimum amount of nuclear material in order for the chain reaction to be self-propelled and, thus, for the bomb to explode.
From fission to fusion
Those discussed so far are the "classic" atomic bombs, based precisely on fission. Generally, the atomic bomb has a trigger that is based on a chemical explosion, which compresses a mass of uranium or plutonium until it reaches critical density. When it reaches it, the chain of fission reactions takes place. Later, however, developments in this area of research led to another type of nuclear device, called fusion bombs. These are the so-called thermonuclear bombs, in which a sequence of two explosions takes place. The primary explosion is equivalent to a fission bomb, with the above sequence of chemical explosion and chain of fissions. The energy released by the primary explosion then leads to a secondary explosion, harnessed to trigger the fusion of hydrogen atoms. The most powerful device of this type ever devised and tested is the well-known Soviet Tsar bomb.
How the explosion happens
We all have the image of the atomic mushroom in our minds. But how does it originate? As soon as the 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 even up to tens of kilometers away from the trigger point. This very fiery sphere, as it rises into the atmosphere, creates the typical mushroom shape. Thermal flash occurs, the heat emitted by this fiery sphere can ignite fires and cause burns even kilometers away from the center of the explosion (depending on the power).
Expanding so rapidly, the explosion creates a shockwave, a sudden change in atmospheric pressure that propagates until it dissipates but creates much of the destruction associated with atomic bombs along the way. Perhaps the peculiarity of atomic bombs, however, is the radioactive fallout, a shower of fission products that spread over the area surrounding the explosion and can contaminate it with radioactive elements for decades at a time.
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