This blog post examines the physical principles through which nuclear fission and fusion release immense energy, and outlines the process by which this energy is converted into the destructive power of atomic and hydrogen bombs within a historical scientific context.
The nuclear issue is a hot potato for the international community and is considered one of the challenges requiring joint efforts by multiple nations. The reason for such high interest in nuclear weapons is, without question, the danger they pose. The atomic nucleus, located at the center of an atom, and the nuclear weapons that utilize it—further, as can be inferred from Einstein’s adage that “the weapons of the Fourth World War will be stones and clubs”—how exactly do these nuclear weapons, possessing such immense destructive power, operate to contain such extreme danger?
Nuclear weapons refer collectively to weapons that utilize the vast amounts of energy released by nuclear fission or fusion reactions within atomic nuclei. Missiles or bombers designed to carry nuclear warheads are also broadly included under the term nuclear weapons. Nuclear weapons are categorized based on their range: strategic nuclear weapons, designed for long-range strikes, and tactical nuclear weapons, which have a relatively shorter range. The nuclear warheads used in these weapons are primarily divided into atomic bombs and hydrogen bombs. Atomic bombs and hydrogen bombs differ in their fundamental principles for generating energy. Atomic bombs utilize the energy released from nuclear fission reactions within atomic nuclei, as follows.
Neutrons that are not bound to an atomic nucleus and can be absorbed by another nucleus are called ‘free neutrons’. When a heavy atomic nucleus, such as uranium or plutonium, collides with such a free neutron, it splits into two lighter atomic nuclei. Since the mass of the parent nucleus is greater than the combined mass of the two resulting nuclei, enormous energy is released according to Einstein’s mass-energy equivalence principle (E = mc²). Simultaneously with the energy release, harmful radiation is emitted, and 2 to 3 additional neutrons are released. These emitted neutrons are called ‘incident neutrons,’ and these incident neutrons collide with other atomic nuclei, triggering further fission reactions. This repeated process is called a chain reaction. The chain reaction continuously triggers nuclear fission, enabling the generation of enormous amounts of energy.
While the power of an atomic bomb is considered to be around 2 kilotons or more, the power of a hydrogen bomb reaches a staggering 1,000 kilotons or more. The secret to this overwhelming power lies in nuclear fusion reactions. Hydrogen fusion reactions occur in environments exceeding 100 million degrees Celsius. A hydrogen bomb uses an atomic bomb as an initiator to artificially create this extreme heat, then triggers a fusion reaction to maximize its destructive power.
There are several types of hydrogen existing on Earth. Examples include ordinary hydrogen, whose nucleus consists of only one proton; deuterium, composed of one proton and one neutron; and tritium, made up of one proton and two neutrons. The nuclear fusion reaction occurring in a hydrogen bomb primarily involves deuterium and tritium. When these two nuclei fuse, helium and neutrons are produced. The resulting mass deficit then releases enormous energy according to the mass-energy equivalence principle (E = mc²). Deuterium is relatively easy to obtain from water on Earth, as approximately 0.0156 percent of water molecules are heavy water containing deuterium. Tritium, however, exists almost nowhere in nature and is therefore produced artificially using lithium. Tritium can be obtained by bombarding lithium with neutrons produced in preceding fusion processes.
Thus, the tritium obtained from the deuterium-lithium reaction undergoes further fusion reactions. The immense energy released as this process repeats becomes the primary energy source of the hydrogen bomb.
Nuclear weapons, especially those utilizing nuclear fusion technology, demand extremely high technical capabilities. Consequently, research and attempts to weaponize them are relatively recent in human history. It was not until the 1930s that the principles of nuclear fission were scientifically elucidated, after which full-scale research into harnessing nuclear energy began. Direct research into developing nuclear weapons intensified in 1945 during World War II through the United States’ “Manhattan Project.” As a result, the United States succeeded in developing atomic bombs using uranium and plutonium. The “Little Boy” and “Fat Man” bombs, which ended the Pacific War and liberated the Korean Peninsula from Japanese colonial rule, were the products of this effort.
Research into nuclear weapons continued in various countries thereafter. On November 1, 1952, the United States successfully conducted the first hydrogen bomb test utilizing nuclear fusion reactions. Subsequently, in August 1953, the Soviet Union succeeded in testing a hydrogen bomb in a form suitable for deployment, formally entering the competition to develop nuclear fusion weapons. In the modern era, five nations—the United States, the United Kingdom, Russia, France, and China—are officially recognized as nuclear-weapon states under the Nuclear Non-Proliferation Treaty (NPT). India, Pakistan, Israel, and North Korea are also recognized by the international community as de facto nuclear-weapon states.
Nuclear weapons represent the pinnacle of modern science and technology. The sheer technical difficulty is evident even from the conditions required for nuclear fusion technology alone, which demands technologies and materials capable of withstanding ultra-high temperatures exceeding 100 million degrees Celsius. Yet, these highly advanced scientific achievements have now become a source of global concern and anxiety. Throughout history, the development of science and technology has been described as a double-edged sword, and nuclear weapons are a prime example of this.
The benefits science and technology bring to human life are truly immense. Yet, the potential negative impacts that can arise simultaneously are equally undeniable. Therefore, for modern people living in this era of advanced science and technology, the essential task remains the effort to minimize the negative aspects of science and technology based on ethical thinking. Without such reflection and a sense of responsibility, nuclear weapons clearly demonstrate that the advancement of science and technology can turn back on humanity not as prosperity, but as a threat.
