By: Leyuan Zhou
As the world reflects on the 75th anniversary of the atomic bomb explosion that devastated Hiroshima in August of 1945, it is important to emphasize the scientific history behind the deleterious mushroom cloud, one of science’s most disturbing successes.
The invention of the atomic bombs dropped by the United States on Hiroshima and Nagasaki hastened the end of World War II, but also created a weapon with the potential to annihilate the entire planet. Although the presence of the nuclear bombs generated geopolitical tension for decades, the scientific story of how exactly the bombs came into existence is still quite intriguing.
Nuclear energy, a fundamental aspect of the atomic bomb, first came into light when Henri Becquerel discovered radioactivity in 1896. The new form of energy was something never seen before, because it consisted of the smallest components of matter - the parts that made up atoms.
The discovery of radioactivity later led to the discovery of nuclear fission, the source of the atomic bomb’s explosiveness, in 1938, around seven years before the bombing of Hiroshima.
At first, the scientific world perceived subatomic energy as a hazy subject - there was no clear clue as to how it could be of any significant use. In 1921, Physicist Robert Millikan wrote in Science News Bulletin that one gram of radium emits 300,000 times as much energy in the process of disintegrating into lead than the burning of one gram of coal. Although he warned about its effects, Millikan undermined the power of radium, considering there wasn’t enough of it present in the world to even make much popcorn.
By 1911, Ernest Rutherford had discovered the nucleus, the place where most of the atom’s energy was stored. The tool for releasing the nuclear power was later discovered a few years later by James Chadwick in the form of a subatomic particle called the neutron. Because the neutron had no electric charge, it had the ability to penetrate the atom and destabilize its nucleus, causing a nuclear fission.
Niels Bohr and John Archibald Wheeler, two physicists who collaborated at Princeton University, eventually discovered that uranium 235, a naturally occurring isotope, induced fission more often than the common uranium-238. Their analyses also revealed that an undiscovered element, uranium -95, was efficient at fissioning.
As World War II grew imminent, physicists could not help but discuss the possible option of a fission bomb. “The threat of war was getting closer and closer,” Said Wheeler in a later interview in 1985. “It was impossible not to think about what this business could mean in the event of war.”
As the word of fission reached the United States, J. Robert Oppenheimer, a leading physicist at University of California, Berkeley, led and assembled the team that was responsible for designing and building the prototype of the atomic bomb. The prototype, exploding in Alamogordo, N.M. in July 1945, proved to be a weapon more terrifying than anything encountered before by humankind.
It is still mind boggling to think about how the discovery of radioactivity, the atomic nucleus, and the neutron would result in the atomic bomb, the world’s most potent weapon of mass destruction.
Article Source: https://www.sciencenews.org/article/atomic-bomb-physics-fission-hiroshima-anniversary