Nuclear fission bomb

Nuclear fission bombs or atomic bombs make use of fission by fast... 

This process, often called a nuclear fusion, has been found to be self-sustaining if a mixture of deuterium and tritium is detonated by the high temperature produced by a nuclear fission bomb. 

Radiocarbon and tritium can be used to determine the approximate age of water masses. Three age—depth zones were deduced from the distribution of tritium and C in the groundwater. As shown in Fig. 19 B, there is an upper zone containing tritium that extends from the water table down to a depth of 6—21 m. The levels of tritium indicate that the source is probably fallout from atmospheric nuclear-fission bomb tests. Inasmuch as the testing of fission devices began in 1954, the age of water in this depth zone is probably less than 25 yr. An intermediate zone in which tritium is absent but radiocarbon is detected extends to a depth of 75m below the upper zone. If the possibility of loss of by mechanisms other than radioactive decay is neglected, a residence time of 10 —10 yr. is indicated. The deepest zone contains no detectable radiocarbon. It is in this zone that the regional groundwater flows system moves to the northeast, as previously indicated on section A—A. ... 

The hydrogen bomb uses a similar type of fusion reaction as its source of energy. A conventional nuclear fission bomb is used as the heat source to start the fusion (thermonuclear) reaction. It may some day be possible to ignite a thermonuclear bomb reaction without a fission bomb, but at this time, no one has a practical notion as to how it might be accomplished. As a result, fusion reactors cannot lead to the production of hydrogen bombs. 

See Haynes 1994. Most influential for the shift to biology and biological hubris was H. G. Wells s The Island of Doctor Moreau (1896), which became the basis for many films. However, Wells continued to use mad chemists , as in The Food of Gods, and How it Came to Earth (1904) and The World Set Free (1914). The latter novel is interesting not only because it was an apocalyptic call for World War I, but also because it narrates a history of chemistry that culminates in the development of a kind of nuclear fission bomb. Whereas this appears to anticipate the discovery of nuclear fission by the chemists Hahn and Strassmann in 1939, later mad scientist stories featured physicists as bomb-makers. 

Consider a large quantity of uranium-235 divided into two pieces, each having a ma.ss smaller than critical. The units arc subcritical. Neutrons in cither piece readily reach the surface and escape before a sizable chain reaction builds up. If the pieces are suddenly pushed rogether, however, the total surface area decreases. If the timing is right and the combined mass is greater than critical, a violent explosion takes place. This is what happens in a nuclear fission bomb, as Figure 4.25 shows. 

In a nuclear fission bomb the critical mass is kept separated into several smaller subcritical masses until detonation, at which time the masses are... 

The step from nuclear fission to a nuclear chain reaction and the atomic bomb was, in principle, quite straightfoiward. In practice, however, it consumed more time and money than was ever foreseen. Although it was her basic insight that eventually led to the fission bomb dropped on Hiroshima, Meitner refused to work on the bomb and, for humanitarian reasons, hoped that it would not work. 

Nuclear fission is also involved in nuclear weapons. To create a bomb, the concentration of the isotope uranium-235 must be increased to at least 85 percent from its natural concenti ation of only 0.7 percent. This increase ot concentration is difficult and expensive. In a typical nuclear reactor the uranium-235 concentration in the fuel is only 3 to 4 percent, and hence a nuclear reactor cannot explode like a bomb. In a nuclear bomb... 

The products of nuclear fission reactions are radioactive and disintegrate according to their own time scales. Often disintegration leads to other radioactive products. A few of these secondary products emit neutrons that add to the pool of neutrons produced by nuclear fission. Very importantly, neutrons from nuclear fission occur before those from radioactive decay. The neutrons from nuclear fission are termed prompt. Those from radioacth e decay arc termed delayed. A nuclear bomb must function on only prompt neutrons and in so doing requires nearly 100 percent pure (or Pu) fuel. Although reactor... 

The process of nuclear fission was discovered more than half a century ago in 1938 by Lise Meitner (1878-1968) and Otto Hahn (1879-1968) in Germany. With the outbreak of World War II a year later, interest focused on the enormous amount of energy released in the process. At Los Alamos, in the mountains of New Mexico, a group of scientists led by J. Robert Oppenheimer (1904-1967) worked feverishly to produce the fission, or atomic, bomb. Many of the members of this group were exiles from Nazi Germany. They were spurred on by the fear that Hitler would obtain the bomb first Their work led to the explosion of the first atomic bomb in the New Mexico desert at 5 30 a.m. on July 16,1945. Less than a month later (August 6,1945), the world learned of this new weapon when another bomb was exploded... 

A nuclear fission explosion. Such a dramatic and destructive release of energy had never been seen before the development of the "atomic bomb" during World War II. 

For nuclear fission to result in a chain reaction, the sample must be large enough so that most of the neutrons are captured internally. If the sample is too small, most of the neutrons escape, breaking the chain. The critical mass of uranium-235 required to maintain a chain reaction in a bomb appears to be about 1 to 10 kg. In the bomb dropped on Hiroshima, the critical mass was achieved by using a conventional explosive to fire one piece of uranium-235 into another. 

The potential of nuclear fission was first realized in the atomic bomb. In 1945, the United States dropped two bombs of unprecedented power, one on Hiroshima and the other on Nagasaki, Japan. Both were fission weapons. 

A nuclear bomb is a terrifying example of the enormous amount of energy released by nuclear fission. A bomb, however, is not the only way to extract the energy produced by nuclear fission. Instead, nuclear fission can be used... 

A hydrogen bomb, which uses nuclear fusion for its destructive power, is three bombs in one. A conventional explosive charge triggers a fission bomb, which in turn triggers a fusion reaction. Such bombs can be considerably more powerful than fission bombs because they can incorporate larger masses of nuclear fuel. In a fission bomb, no component of fissionable material can exceed the critical mass. In fusion, there is no critical mass because fusion begins at a threshold temperature and is independent of the amount of nuclear fuel present. Thus, there is no theoretical limit on how much nuclear fiiel can be squeezed into a fusion bomb. 

Understanding fusion invites another question If fusing nuclei releases energy, how did the early atomic bombs work In those bombs, nuclei were not fused, they were broken apart by nuclear fission. So, where does the energy of atomic bombs come from An important piece of the answer came from a brilliant Jewish scientist who fled Nazi Germany shortly before World War II. 

It is highly improbable that a nuclear fission power plant would ever explode like a nuclear bomb, but a loss of coolant accident could result in a melt down condition. In a melt down, a large amount of radiation can be released at ground-level. A nuclear or conventional chemical or steam explosion could disperse much of the radioactive particles into the atmosphere. This is essentially what happened when the Chernobyl gas explosion occurred in the Soviet Union in 1986. 

A heavy nucleus can split into lighter nuclei by undergoing nuclear fission. Nuclear power plants use controlled nuclear fission to provide energy. Uncontrolled nuclear fission is responsible for the massive destructiveness of an atomic bomb. 

Because the isotope uranium-235 is fissionable, meaning that it produces free neutrons that cause other atoms to split, it generates enough free neutrons to make it unstable. When the unstable U-235 reaches a critical mass of a few pounds, it produces a self-sustaining fission chain reaction that results in a rapid explosion with tremendous energy and becomes a nuclear (atomic) bomb. The first nuclear bombs were made of uranium and plutonium. Today, both of these fuels are used in reactors to produce electrical power. Moderators (control rods) in nuclear power reactors absorb some of the neutrons, which prevents the mass... 

One day as the Italian physicist Enrico Fermi and George Uhlenbeck (who had come to the United States on a visit) were looking out a window overlooking Manhattan, Fermi remarked, You realize, George, that one small fission bomb could destroy most of what we see outside Fermi was soon to be doing some of the preliminary experimental work that preceded the American atomic bomb project. It was Fermi who produced the first controlled nuclear chain reaction. 

Niels Bohr was a physicist, not a chemist. I devote a chapter to his life because he was the scientist who explained why Mendeleev s periodic table had the properties it did. Widely known as a soccer player in his youth, Bohr became the most influential physicist of the first half of the twentieth century. His life, too, was touched by political events. A Jew living in occupied Denmark, Bohr had to flee the country to avoid arrest by the Nazis. In 1939 Bohr discovered a theory that explained nuclear fission, and suggested that uranium 235 could be used to make a bomb. Though he played only a minor role in the American atomic bomb project, Bohr was the first to ponder the political implications of the bomb. 

J Ju elements in the periodic table exist in unstable versions called radioisotopes (see Chapter 3 for details). These radioisotopes decay into other (usually more stable) elements in a process called radioactive decay. Because the stability of these radioisotopes depends on the composition of their nuclei, radioactivity is considered a form of nuclear chemistry. Unsurprisingly, nuclear chemistry deals with nuclei and nuclear processes. Nuclear fusion, which fuels the sun, and nuclear fission, which fuels a nuclear bomb, are examples of nuclear chemistry because they deal with the joining or splitting of atomic nuclei. In this chapter, you find out about nuclear decay, rates of decay called half-lives, and the processes of fusion and fission. 

Nuclear flssion Nuclear fission, the splitting of an atomic nucleus, doesn t occur in nature. Humans first harnessed the tremendous power of fission during the Manhattan Project, an intense, hush-hush effort by the United States that led to the development of the first atomic bomb in 1945. Fission has since been used for more-benign purposes in nuclear power plants. Nuclear power plants use a highly regulated process of fission to produce energy much more efficiently than is done in traditional, fossil fuel-burning power plants. 

Another example of a nuclear fission explosion is the explosion of an atomic bomb. Nuclear fission explosions may also take place in a nuclear reactor if a breakdown occurs and a critical mass is achieved. 

Fission weapons or bombs They derive their power from nuclear fission when heavy nuclei such as uranium (U) or plutonium (Pu) are bombarded by neutrons and split into lighter elements, more neutrons and energy. The newly generated neutrons then bombard other nuclei which then split and bombard other nuclei and so on. This process continues and leads to a nuclear chain reaction which releases large amount of energy. These are also historically called atomic bombs or atom bombs or A-bombs. 

The distinction between these two types of weapons is blurred because they are combined in almost all advanced modern weapons. For example, a smaller fission bomb is first used to create necessary conditions of high temperature and pressure which are required for fusion. Similarly, fusion elements may also be present in the core of fission devices as well because they generate additional neutrons which increase efficiency of the fission reaction. Further, most of the fusion weapons derive substantial portion of their energy from a final stage of fissioning which is facilitated by the fusion reactions. The simplest nuclear weapons are pure fission bombs. They were the first type of nuclear weapons built during the American Manhattan Project and are considered as a building block for all advanced nuclear weapons. 

Is it possible for a nuclear fission power plant to blow up like an atomic bomb ... 

If in the explosion of one atom bomb 50.0 g of 299Pu were scattered about in the atmosphere before it had a chance to undergo nuclear fission, how much... 

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