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A nuclear weapon is an explosive device that acquires its devastating power from fission and/or fusion nuclear reactions. These reactions release huge amounts of energy from relatively small amounts of matter. Also called weapons of mass destruction, nuclear weapons are a topic of great debate and controversy around the world. Many countries currently have arsenals with several nuclear warheads that they are prepared to launch at any given moment. They are the most dangerous and devastating weapons known to mankind with the potential to kill and severely injure millions of people within a short time period.
When scientists first began experimenting with nuclear reactions in the 20th century, none would anticipate the quick progress and future applications of their research. With many great advancements in science and especially nuclear chemistry, nuclear weapons have been developed.
Types of Nuclear Weapons
The atomic bomb is one of two main types of nuclear weapons and can also be called A-bombs or atom bombs. It produces explosive energy through nuclear fission reactions in which the nucleus of an atom is split into smaller fragments. When bombarded with neutrons in a particle accelerator, the nucleus of the uranium or plutonium atom will split into smaller fragments; this releases a vast amount of explosive energy and emits a number of neutrons that bombards other atoms, creating a chain reaction. In these weapons enough fissile material like enriched uranium or plutonium, that is greater than the critical mass (the amount of material where the chain reaction becomes self-sustaining) must be gathered. There are two major designs of atomic bombs. One design is the gun-type assembly method in which one piece of sub-critical material is shot into another piece. Another design is the implosion assembly method in which the uranium or plutonium is severely compressed with the use of chemical explosives. Most atomic bombs utilize uranium-235 which has a high fission probability.
A hydrogen bomb is the other main type of nuclear weapon and is also referred to as a thermonuclear weapon or an H-bomb. This bomb gains its explosive force through nuclear fusion reactions in which light atomic nuclei with lower atomic numbers join together forming a heavier nucleus. Specifically, the fusion in a hydrogen bomb involves two isotopes of hydrogen, deuterium and tritium, which fuse to form the nucleus of helium and one neutron. This fusion produces 17.6 MeV of energy. Although there is a limit on the amount that fission can occur, there is no limit on the amount of fusion that can occur. The hydrogen bomb has a primary and secondary stage. In the primary stage, a fission bomb releases radiation and neutrons. The radiation and neutrons from the fission bomb react to compress the lithium deuteride in the second stage, producing tritium and thus allowing for the process of fusion.
Another type of nuclear weapon is the neutron bomb, a small hydrogen bomb. Also known as an enhanced radiation weapon, the neutron bomb has reduced blast and heat effects. Unlike standard nuclear weapons that are designed to destroy using explosive energy, the neutron bomb's primary lethal effects are derived from the radiation damage.
Nuclear Weapon Effects
Nuclear weapons can be thousands or millions of times greater more powerful than other conventional types of explosions. A nuclear detonation has a variety of effects including blast, thermal pulse, neutrons, x- and gamma-rays, radiation, electromagnetic pulse (EMP), and ionization of the upper atmosphere. Depending on where the nuclear weapon is detonated, blast effects can cause ground shock, water shock, the creation of craters, and significant amounts of dust and radioactive fallout.
The energy of a nuclear explosion affects an area in three different ways: blast, thermal radiation, and nuclear radiation. In a low altitude atmospheric detonation of a normal-sized weapon in the kiloton range, 50% of the energy is released in the air blast, 35% as thermal radiation, and 15% as various types of nuclear radiation. In the air blast, a shock wave of air radiates outward, thus suddenly changing the air pressure and causing high winds. Buildings are destroyed by the air pressure and smaller things like people or trees are destroyed by the force of the wind or the heat of the fire. The thermal radiation, or heat, can cause a brief period blindness or retinal burn to those watching the explosion. The intensity of the heat is even capable of causing severe burns miles away from the site of detonation. The blast of heat is most destructive because it sparks conflagrations in many other areas, igniting fuel sources that it comes in contact with.> While the direct nuclear radiation is lethal to humans nearby, the fallout radiation, radioactive particles that scatter far from the site of detonation is extremely toxic or even lethal to humans, animals, and plants that are not located near the site. The radiation may continue to be emitted for long periods of time after the explosion, still posing a health threat.
The history of nuclear weapons begins with the discovery of the structure of an atom. In 1919, Ernest Rutherford achieved the first official artificial transmutation of an element by changing several nitrogen atoms into oxygen atoms. This discovery sparked a series of new atomic discoveries including the discoveries of protons and neutrons. Particle accelerators were soon developed in the early 1930's in an attempt to bombard the nuclei of various elements to disintegrate atoms. Lawrence's cyclotron, the Cockroft-Walton machine, and Van de Graaff's electrostatic generator were particle accelerators that required huge amounts of energy to split atoms. Renowned scientists Ernest Rutherford, Albert Einstein, and Niels Bohr all regarded particle bombardment as useful in understanding nuclear physics. However, the huge amounts of energy required for the particle accelerators of the time caused those scientists to regard the practical use of atomic power in the near future as impossible.
The Discovery of Fission
It was not long after Rutherford, Einstein, and Bohr expressed their doubts before those doubts were proved incorrect. In 1934, the Italian physicist Enrico Fermi successfully bombarded atoms by using neutrons instead of protons, based on Chadwick's theory that uncharged particles could pass into the nucleus without resistance. One of the elements he transmutated was uranium; this produced substances that scientists could not confidently identify and that were the subject of great debate. Otto Hahn and Fritz Strassmann, two radiochemists from Berlin, solved the debate in an accidental discovery before Christmas 1938. Like Enrico Fermi, the scientists had been bombarding elements with neutrons. They discovered that when uranium was bombarded with neutrons, the uranium nuclei broke into two almost equal pieces. Other elements had not shown such a change. The products created were radioactive barium isotopes and uranium fragments that weighed less than the original uranium nuclei. Gleaning from Einstein's theory of mass and energy, Lisa Meitner, a colleague of Hahn, and her son concluded that the decrease in mass was due to a major conversion from mass to heat energy. Hahn and her son named the process nuclear fission, defining it as the splitting of an atom's nucleus to produce smaller fragments.
Nuclear fission provided the possibility of ever-increasing amounts of energy. The fission of one atom released an enormous amount of energy. Yet it also caused the emission of neutrons, which consequently bombarded with other atoms to repeat the fission process. This chain reaction had the potential to generate a large, continuous amount of energy in a controlled reaction or to generate an explosion of huge force in an uncontrolled reaction.
World War II
The Manhattan Project
After being informed by Neils Bohr about the new discoveries regarding nuclear fission, American scientists actively took leadership in the nuclear physics field. Ernest Lawrence was one of the main scientists of the age whose particle accelerator helped to establish the United States and especially the Berkeley Radiation Laboratory as the unofficial capital of nuclear physics in the world. Renowned scientists tirelessly experimented with the nuclear process. In 1939 Einstein wrote a letter to President Roosevelt, urging him to investigate the use of nuclear fission to produce bombs and also warning the president that Nazi Germany was investigating the idea of nuclear bombs as well. President Roosevelt responded to Einstein's warning by calling for the formation of the Advisory Committee on Uranium in October 1939. This committee was extremely active in achieving funding for the creation of an atomic bomb. In 1941, a plan in the MAUD Report was proposed that outlined the supplies and steps needed to create the first atomic bomb. The Uranium Committee attained funding and approval for more research on this subject. Roosevelt later approved the involvement of the U.S. Army in October 1941, providing more funding for the advancement of the atomic bomb. The top-secret government program came to be called the Manhattan Project with the goal specifically to create a nuclear bomb. After a few years, the Manhattan Project conducted the world's first nuclear test on July 16, 1945. The test, codenamed 'Trinity', occurred at the Alamogordo Test Range, a desert area in New Mexico. There have been no other nuclear tests at that site since then. 
Toward the end of WWII, the Japanese were clearly losing the war. The United States issued the Postdam Proclamation which demanded that the Japanese surrender unconditionally or face destruction. Japan rejected the proclamation on July 29, 1945. In order to avoid sending U.S. troops into Japan or spending significant funds bombing Japan, President Truman decided to use nuclear bombs to force the Japanese to surrender quickly. Although the U.S. intended to drop the bombs as early as August 1, the weather made it impossible for them to do so. The first bomb was dropped on August 6, 1945 on Hiroshima, Japan. An American B-29 bomber named the Enola Gay delivered Little Boy, a uranium 235 gun-type bomb. The explosion at 8:16 AM instantly killed 80,000 to 140,000 people were killed and seriously injured another 100,000. The second bomb was dropped in Nagasaki on August 9, 1945 by the American B-29 bomber, Bock's Car. The bomb, called Fat Man, was aimed for the Mitsubishi Torpedo Plant. It exploded at 11:02 AM, killing 74,000 people and leaving 75,000 with sustained severe injuries. Following the attacks, the Japanese emperor Horotito convened an Imperial Conference and officially announced Japan's surrender at noon on August 15, 1945. This was the end to WWII.
Post World War II
Since World War II, nuclear weapons have not been used. In January 1946, the General assembly of the United Nations passed its first resolution, calling for the elimination of all weapons of mass destruction from national arsenals. This resolution was unsuccessful however, because many countries soon began research into nuclear weapons soon after.
At the end of World War II, the U.S. started a series of tests at Bikini Atoll, an island of coral that encircles a lagoon partially or completely in the Pacific Ocean. They aimed to discover more about the nuclear weapons and about the effects on personnel and equipment if a nuclear bomb were to be used. In 1950, the U.S. began the development of the hydrogen bomb with the leadership of Edward Teller, an important physicist who had previously worked on the Manhattan Project. After the U.S. began researching nuclear weapons, other countries soon followed and investigated nuclear weapons. The Soviet Union had its first test in 1949 in Kazakhstan, Britain followed in 1952 in Australia, France also joined in 1960 in the Algerian desert, and China finally followed in 1964 in Lop Nor. Most countries carried out a series of tests in the open rather than underground. The U.S. eventually moved all their testing to the Nevada desert, where the British would soon transfer their testing in 1962. France also established test sites at Muroroa and Fangataufa Atolls in the Pacific Ocean.
The Cold War
From the 1950's until the 1980's, the United States and the Soviet Union, the two superpowers of the time, continued to develop their nuclear arsenals. Each justified the buildup of nuclear warheads by stating that the threat of massive retaliation from the other would ensure that they would never be used. In other words, the consequence of using nuclear warheads would be too great for either country. Both countries were deeply suspicious of each other during this time with several instances where one country prepared to detonate when the other country seemed prepared to detonate.
In the Cuban Missile Crisis of 1962, the Soviet Union was placing nuclear missiles in Cuba, which was a mere 90 miles from the U.S. coast at Florida. The U.S., feeling extremely threatened by this, almost forged a nuclear war. In 1985, Mikhail Gorbachev, the Soviet leader of the time, signed a treaty to get rid of several nuclear weapons. The situation seemed to become more optimistic. However, the threat continued during the Gulf War when it was suspected that Iraq would use chemical or biological weapons on Israel with a similar retaliation from Israel. 
Many treaties and organizations have been formed with the purpose of nuclear disarmament; some examples include the International Atomic Energy Agency and the Comprehensive Test Ban Treaty. The Comprehensive Test Ban Treaty outlaws any kind of nuclear testing. This treaty was intended to be signed and ratified by 44 countries identified as having nuclear power plants or research reactors. Of those 44 countries, only 31 have ratified the treaty. Ten countries have signed without ratifying (as of 2003) including Algeria, China, Colombia, Democratic Republic of Congo, Egypt, Indonesia, Iran, Israel, USA, and Viet Nam. Three countries have refused to sign it so far including India, Pakistan, and North Korea. With more countries building up arsenals of nuclear weapons, the threat of nuclear warfare is great, especially between countries with strained relations. The effects of nuclear weapons has had and will continue to have a global impact. The threat is high and the consequences could be fatal to millions of people, if not billions.
- ↑ 1.0 1.1 1.2 1.3 Wikipedia:Nuclear_weapon By Wikipedia
- ↑ The Manhattan Project: Making the Atomic Bomb Part I: Physics Background, 1919-1939
- ↑ Nuclear Fission: Critical Mass
- ↑ Why Uranium and Plutonium?
- ↑ 5.0 5.1 Nuclear Fusion
- ↑ The Energy from a Nuclear Weapon
- ↑ 7.0 7.1 Nuclear Weapon Effects By FAS
- ↑ 8.0 8.1 8.2 Basic Effects of Nuclear Weapons
- ↑ Nuclear Radiation
- Also Digital Library for Nuclear Issues Washington and Lee University.
- History of Nuclear Weapons Come Clean: WMD Awareness Programme.
- Manhattan Project Wikipedia.org.
- Nuclear Files NuclearFiles.org: A project of the Nuclear Age Peace Foundation.
- Nuclear Weapon Wikipedia.org.
- Nuclear Weapon Effects Federation of American Scientists.
- The Effects of Nuclear Weapons Atomicarchive.com.
- The Manhattan Project: Making the Atomic Bomb Atomicarchive.com.
- The Nuclear Weapon Archive: A Guide to Nuclear Weapons Nuclearweaponarchive.org.