The scientific secret behind the dual nature of the atomic bomb

By Jaesun Yang ’27 • Dec 5, 2025

Mushroom Cloud and Oppenheimer

My favorite movie is Oppenheimer, directed by Christopher Nolan. The film Oppenheimer tells the story of Julius Robert Oppenheimer, the father and creator of the atomic bomb, beginning before the development of the bomb, continuing through the process of creating it, and following him afterward as he confronts the horrific consequences caused by his invention. The movie centers on his deep guilt and the complex conflict between scientific progress and ethical responsibility. The development of the atomic bomb began during World War II after the attack on Pearl Harbor and the beginning of the Pacific War. Later, near the end of World War II, the United States dropped one bomb each on Hiroshima and Nagasaki, revealing to the world the horrifying and brutal reality hidden behind the brilliant and dazzling image of the atomic bomb — the darkest depths of humanity’s endless greed. What scientific secrets lie within the atomic bomb that give it such a dual nature? Let’s find out together.

The Scientific Principle Behind the Atomic Bomb

Bomb Structure Diagram

The atomic bomb operates using the principle of nuclear fission. When a neutron collides with the nucleus of elements such as Uranium-235 (U-235) or Plutonium-239 (Pu-239), the nucleus splits into two new nuclei. We call this process nuclear fission. As the nucleus absorbs neutron radiation, the fission reaction does not stop; instead, the newly split nuclei can undergo additional nuclear fission repeatedly, creating an endlessly self-sustaining chain reaction. However, even without absorbing neutron radiation, spontaneous fission can occur. The neutrons produced during this process become a key factor in triggering the chain reaction. Although spontaneous fission happens extremely rarely, if it does occur, the number of neutrons becomes greater than the number of atoms being split, causing the reaction to grow explosively in a pattern such as 1 - 2 - 4 - 8-...  As this chain reaction expands rapidly, an enormous amount of energy is released all at once. This follows Einstein’s theory of relativity, E = mc², meaning that the energy released comes from the mass lost during the nuclear fission process. When the massive amount of energy generated from this process is released simultaneously, it results in an extremely powerful explosion. The mushroom cloud many of us have heard of or seen in historical images is the visual result of this large-scale nuclear explosion.

The Power of the Atomic Bomb

Mushroom Cloud Over Nagasaki

Even after reading the previous explanation, it is still difficult to fully grasp the destructive power of an atomic bomb. In fact, if such a nuclear weapon were to explode in Seoul, many sources predict that everyone within a 2.5 km radius would be killed instantly. The power of an atomic bomb is usually measured in comparison to the explosive strength of TNT. The atomic bomb dropped on Hiroshima, Japan, had a yield of approximately 15 kt (kilotons) of TNT, while the bomb dropped on Nagasaki is estimated to have had a yield of about 21 kt.  When the atomic bomb detonated in Hiroshima, a deafening explosion was followed by an intense flash of light and a massive firestorm. Approximately 70,000 people died instantly, and hundreds of pillars of fire swept across the ground, destroying homes and buildings in an instant.