Nuclear Weapons are explosive weapons that gain their explosive power from nuclear reactions. Nuclear weapons generate much more energy than weapons using chemical explosives such as TNT. Nuclear weapons can be in the form of aerial bombs, artillery shells, or missiles warheads. Nuclear devices can be exploded in the atmosphere or on or under a land or water surface. A nuclear explosion immediately creates a luminous fireball consisting of ionized matter. The explosion also creates a powerful blast wave. In an atmospheric explosion, the fireball rapidly rises and forms a mushroom-shaped cloud. The blast wave moves away from the fireball at supersonic speed and can demolish buildings over large areas. Heat emitted by the fireball can cause serious skin burns and even start fires from a great distance (Cimbala, 2002). The explosion also produces highly penetrating nuclear radiation that can cause serious illness or death. Radioactive matter created during the explosion can leave a region virtually uninhabitable for some time. The devastating power of nuclear weapons has twice been unleashed on mankind. On August 6, 1945, during the World War II, a United States B-29 bomber dropped a 9,000-pound (4,082-kg) nuclear device on Hiroshima, Japan. The explosion of this atomic bomb (as the weapon was called) resulted in a huge number of deaths—the exact figures are unknown, but estimates range from 68,000 to 200,000 persons. The city was largely destroyed. On August 9, a 10,000-pound (4,536-kg) nuclear device was exploded over the Japanese city of Nagasaki, with similar results (Tsipis, 2004). Five days later the Japanese government surrendered, bringing World War II to an end. The purpose of this paper is to: (1) get to know the in-depth understanding of what nuclear energy really is; (2) be aware of how nuclear weapons work and; (3) be familiar with the effects of nuclear explosions. II. Background A. Nuclear Energy Nuclear energy (also called atomic energy), results from the conversion of mass into energy according to Albert Einstein’s formula E = mc2. (This is read “E equals m c squared.” E represents energy, m mass, and c the speed of light. If the mass is measured in kilograms and the speed of light in meters per second, the result is energy in joules.) The conversion of one kilogram (2.2 pounds) of any substance into energy would produce about 9 X 1016 joules, or 25 billion kilowatt-hours, of energy (Gasteyger, 1999). Nuclear weapon is released when the particles that make up the nucleus (core) of an atom are rearranged in some manner. As the particles are rearranged, a small portion of the mass of the nucleus is converted into energy. Nuclear energy in large amounts has been produced by two processes—fission and fusion. Fission refers to the splitting (fissioning) of a large nucleus into two or more smaller ones. Fusion refers to the building up of a nucleus by combining smaller nuclei or individual protons and neutrons (Gasteyger, 1999). III. Discussion A. How nuclear weapons work? Explosive devices that utilize the fission process were originally called atomic weapons, while those that depend on fusion were known as hydrogen weapons or thermonuclear weapons. These terms are still used occasionally, but the term “nuclear weapons,” which designates both fission and fusion weapons, is used more frequently. Fission Weapons. Only certain typed of atoms have nuclei that can be readily fissioned. Of those that do have a fissionable nucleus, the two most easily produced in quantity for nuclear weapons are uranium 235 (whose nucleus contains a total of 235 protons and neutrons) and plutonium 239. In fission reaction only about 0.1 percent of the mass of the atom is converted into energy (Spector, 2004). Nevertheless, the fissioning of all the atoms in 1 kilogram (2.2 pounds) of either uranium 235 or plutonium 239—a chunk about the size of a golf ball—yields as much energy as would be released by 17,000 tons of TNT. When a sufficient amount of either uranium 235 or plutonium 239 is brought together, a spontaneous, self-sustaining chain reaction occurs. In a chain reaction, the splitting of atomic nuclei causes the emission of particles called neutrons that, in turn, cause other nuclei to split. The amount of uranium or plutonium required, called the critical mass, depends on the composition and shape of the material. In general, plutonium 239 has a smaller critical mass than uranium 235. The critical mass for a solid sphere of plutonium 239 is only about 35 pounds (16 kg). A fission weapon is detonated by very rapidly bringing together more than enough fissionable material to form a critical mass ( Krieger, 2001). The fission reactions proceed through the material at an uncontrolled rate, leading to the release of a tremendous amount of energy within a very short period of time—less than a millionth of a second. There are at least two basic methods used to make a fission bomb explode. In one method, used in the atomic bomb dropped on Hiroshima, two masses of uranium 235 are driven together by a chemical explosive charge. (The two masses must be brought together quickly to prevent the material from blowing apart before most of the uranium undergoes fission. In the second method, used in the bomb dropped on Nagasaki, a number of high explosive charges are used to crush a hollow sphere of plutonium into a dense ball. A major difficulty in constructing a fission weapon lies in the preparation of a supply of fissionable material of adequate purity. Many nations possess the technical ability to develop a fission bomb, but only a few have the necessary resources (Susiluot, 2002). B. Effects of Nuclear Explosions The three effects of nuclear explosions are the blast effect; the thermal effect; and the nuclear radiation effect. Blast and thermal effects are associated with both chemical explosions and nuclear explosions, but only nuclear explosions produce nuclear radiation. The relative strength of each type of effect produced by the explosion of a nuclear weapon in the atmosphere depends on the weapon’s construction. On the average, the energy of such an explosion is 50 percent blast, 35 percent thermal, and 15 percent nuclear radiation (Tsipis, 2004). In the event of a large-scale nuclear war, the explosions produced by the detonation of hundreds or thousands of nuclear weapons would blast a large amount of soil into the air. The explosions would also start widespread fires that would send a large amount of smoke high into the atmosphere. Some scientific studies indicate that such a war could result in a phenomenon commonly referred to as nuclear winter. According to the studies, the dust and smoke might block out the sun for weeks or months, causing temperatures at the earth’s surface to fall well below normal (Smith, 1997). Reduced temperatures, together with the lack of sunlight, could kill much of the plant life that animals feed for food. The nuclear radiation resulting from a nuclear explosion is divided into two categories: (1) initial, or prompt, radiation; and (2) residual, or fallout, radiation. Prompt radiation is radiation that is emitted within one minute of the explosion. All subsequent radiation is termed fallout radiation (Schneider, 2004). IV. Conclusion In conclusion, the concept of nuclear weapons serving as a deterrent was weakened with the introduction of missiles with multiple warheads. These warheads can each be aimed at a different target and are extremely accurate. Some military planners began to speak of a “counterforce” attack—a nuclear attack directed specifically at the nuclear forces of the other country with the intention of reducing its ability to launch a retaliatory strike. Other military planners, however, believe that such an attack could not be made without a great risk of starting a devastating, unlimited nuclear exchange. Reference: Cimbala, Stephen J. A New Nuclear Century: Strategic Stability and Arms           Control. Praeger, 2002. Gasteyger, Curt. Thinking Aloud: Is NPT's Assumption of a Finite Number of      Nuclear-Weapon States Realistic? UN Chronicle, Vol. 36, Summer    1999. Krieger, David. A New Beginning: A World without Nuclear Weapons.    International Journal of Humanities and Peace, Vol. 17, 2001. Smith, Ron. The Abolition of Nuclear Weapons: Possibilities and Practicalities.   New Zealand International Review, Vol. 22, 1997. Schneider, Jr. William. A 21st-Century Role for Nuclear Weapons: New   Security Challenges and Improved Conventional Weapons Mean New           Roles and Requirements for Nuclear Weapons. Issues in Science and Technology, Vol. 20, Spring 2004 Spector, L.S. Nuclear Proliferation Today (Ballinger, 2004). Susiluot , Taina. Tactical Nuclear Weapons: Time for Control. United Nations     Institute for Disarmament Research, 2002. Tsipis, Kosta. Arsenal: Understanding Weapons in the Nuclear Age (Simon &     Schuster, 2004).