Atomic bomb nucleus

The rapid fission of a mass of or another heavy nucleus is the principle of the atomic bomb, the energy liberated being the destructive power. For useful energy the reaction has to be moderated this is done in a reactor where moderators such as water, heavy water, graphite, beryllium, etc., reduce the number of neutrons and slow those present to the most useful energies. The heat produced in a reactor is removed by normal heat-exchange methods. The neutrons in a reactor may be used for the formation of new isotopes, e.g. the transuranic elements, further fissile materials ( °Pu from or of the... 

A second sun, powerful and man-made, was born on July 16, 1945. A ball of fire thousands of times hotter than the surface of the real sun illuminated the New Mexico desert. Its birthplace was the Trinity site, and the explosion was the culmination of years of work by the world s brightest scientists. It was the planet s first atomic bomb, the tangible and frightening outcome of splitting the nucleus of an atom. 

Mysteries such as this attract young people to science. Nuclear physics, however, tends to turn people off Nuclear power plant malfunctions and atomic bombs are frightening. Nevertheless, humankind has greatly benefited from scientific investigations of the nucleus. Science s hard-won knowledge of the atomic nucleus is used extensively in medicine, from imaging procedures such as positron emission tomography (PET) to radiation therapy, which has saved the lives of many cancer patients. 

When the energy in the nucleus of an atom is released, the results are spectacular. Atomic bombs and reactors that power entire cities grab everyone s attention. But most of the everyday world is governed by an atom s electrons, the swirling cloud of negatively charged matter that can act as particles or waves. 

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. 

At the start of the twentieth century, it was discovered that the nucleus is composed of positively charged protons and neutral neutrons (see Chapter 4). These particles are collectively called nucleons. During the last half of the same century, scientists learned how to harness the power of the atom. The deployment of two atomic bombs brought a quick and dramatic end to World War II. This was followed by nuclear proliferation, the Cold War, and the current debate over... 

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. 

The combination of two or more lighter nuclei to form a heavier nucleus is called nuclear fusion. The amount of energy released in fusion reactions is greater than the amount of energy released in fission reactions. However, a huge amount of activation energy (such as an atomic bomb explosion) is needed to initiate nuclear fusion reactions. 

Nuclear Explosions Although conventional explosives have become the weapons of choice of terrorist groups, a joint report issued in 2008 by Harvard s Kennedy School of Government and the Nuclear Threat Initiative reminds us that there is a real danger that terrorists could get and use a nuclear weapon.16 In order to understand what this would mean, we return to the atomic nucleus. A nuclear fission reaction releases far more energy than any ordinary chemical process. The Oklahoma City bomb was equivalent to the explosion of approximately 40001b of TNT.17 In contrast, the atomic bomb dropped on... 

When a neutron enters a sample of 92U, it may collide with the nucleus of one of the atoms, producing a reaction in which two or three new neutrons are produced. Each of these may react with another nucleus, producing more reactions and an increased number of neutrons (Figure 21.5). Such reactions, all started by a single neutron, can continue until the entire sample of has reacted. The sequence of reactions is called a chain reaction and is the source of energy by which nuclear power plants operate. The atomic bomb, which should more accurately be called the nuclear bomb, also uses a chain reaction. 

When the element uranium is bombarded by neutrons, a unique reaction called fission takes place. The uranium nucleus breaks into two pieces, which fly apart with a large release of energy. In addition, several extra neutrons are emitted. These cause more uranium nuclei to split apart, which creates more energy and more neutrons in a so-called chain reaction process. In an atomic bomb, the chain reaction becomes an uncontrolled explosion. In a nuclear power plant, the chain reaction is maintained in a steady state by control rods which absorb extra neutrons. 

Nuclear fission is a process in which the nucleus of an atom splits, usually into two pieces. This reaction was discovered when a target of uranium was bombarded by neutrons. Eission fragments were shown to fly apart with a large release of energy. The fission reaction was the basis of the atomic bomb, which was developed by the United States during World War II. After the war, controlled energy release from fission was applied to the development of nuclear reactors. Reactors are utilized for production of electricity at nuclear power plants, for propulsion of ships and submarines, and for the creation of radioactive isotopes used in medicine and industry. 

The destructive power of nuclear weapons derives from the core of the atom, the nucleus. One type of nuclear weapon, the fission bomb, uses the energy released when nuclei of heavy elements such as plutonium fission (split apart). A second even more powerful type of nuclear weapon, the fusion or hydrogen bomb, uses the energy released when nuclei of hydrogen are united (fused together). 

Neutrons are tiny particles with no charge in the nucleus (center) of almost all atoms. Industrially, they are used to make nuclear fission reactions occur. Nuclear fission is the process in which large atoms break apart. Large amounts of energy and smaller atoms are produced during fission. Fission reactions are used to provide the power behind nuclear weapons (such as the atomic bomb). They are also used to produce energy in a nuclear power plant. 

Nuclear chemistry is very much in the news today. In addition TO APPLICATIONS IN THE MANUFACTURE OF ATOMIC BOMBS, HYDROGEN BOMBS, AND NEUTRON BOMBS, EVEN THE PE.A.CEFUL USE OF NUCLEAR ENERGY HAS BECOME CONTROVERSIAL, IN PART BECAUSE OF SAFETY CONCERNS ABOUT NUCLEAR POWER PLANTS AND ALSO BECAUSE OF PROBLEMS WITH DISPOSAL OF RADIOACTIVE WASTES. IN THIS CHAPTER WE WILL STUDY NUCLEAR REACTIONS, THE STABILITY OF THE ATOMIC NUCLEUS, RADIOACTIVITY, AND THE EFFECTS OF RADIATION ON BIOLOGICAL SYSTEMS. 

With the discovery of the neutron as a fundamental particle, many paradoxes of physics and chemistry were finally resolved, and new areas of research evolved. Prior to the discovery of the neutron as a fundamental particle, scientists generally believed that the nucleus was comprised of protons and nuclear electrons. However, one could not explain, for example, the spin of nuclei with that model. Now, at last, theory could predict the properties of the nucleus quite well. Also, since neutrons are not repelled by the charge on the atomic nucleus, they interact easily with nnclei. Nen-tron scattering enables the determination of crystal stmctnres by probing the positions of nuclei in a sample. Neutrons can also catalyze fission reactions, for example, the fission of uranium nuclei that led to the creation of nuclear power plants and the atomic bomb. 

They didn t need my help in making the atom bomb, Bohr later told a friend. He was there to another purpose. He had left his wife and children and work and traveled in loneliness to America for the same reason he had hurried to Stockholm in a dark time to see the King to bear witness, to clarify, to win change, finally to rescue. His revelation—which was equivalent, as Oppenheimer said, to his revelation when he learned of Rutherford s discovery of the nucleus—was a vision of the complementarity of the bomb. In London and at Los Alamos Bohr was working out its revolutionary consequences. He meant now to communicate his revelation to the heads of state who might act on it to Franklin Roosevelt and Winston Churchill first of all. 

I- n -> La -I- Br -i- 3n The energy released is approximately 3 x 10 J per nucleus. For 1 kg of this is equivalent to 20 000 megawatt-hours - the amount of energy produced by the combustion of 3 X 10 tonnes of coal. Nuclear fission is the process used in nuclear reactors and atom bombs (sccnuclear weapons). 

This branch of chemistry began with the discovery of natural radioactivity by Antoine Becquerel and grew as a result of subsequent investigations by Pierre and Marie Curie and many others. Nuclear chemistry is very much in the news today. In addition to applications in the manufacture of atomic bombs, hydrogen bombs, and neutron bombs, even the peaceful use of nuclear energy has become controversial, in part because of safety concerns about nuclear power plants and also because of problems with radioactive waste disposal. In this chapter, we wiU study nuclear reactions, the stability of the atomic nucleus, radioactivity, and the effects of radiation on biological systems. 

The atomic bomb is a fission bomb it operates on the principle of a very fast chain reaction that releases a tremendous amount of energy. An atomic bomb and a nuclear reactor both depend on self-sustaining nuclear fission chain reactions. The essential difference is that in a bomb the fission is wild, or uncontrolled, whereas in a nuclear reactor the fission is moderated and carefully controlled. A minimum critical mass of fissionable material is needed for a bomb otherwise a major explosion will not occur. When a quantity smaller than the critical mass is used, too many neutrons formed in the fission step escape without combining with another nucleus, and a chain reaction does not occur. Therefore the fissionable material of an atomic bomb must be stored as two or more subcritical masses and brought together to form the critical mass at the desired time of explosion. The temperature developed in an atomic bomb is believed to be about 10 million degrees Celsius. 

To a very good approximation, different isotopes of the same elanent have identical chemical properties however, they can differ in some physical properties, such as density, which depends on mass, and radioactivity, which depends on the ratio of neutrons to protons in the nucleus, as will be discussed in Chapter 17. Two common isotopes of uranium (Z = 92), for example, have mass numbers 235 and 238. The lighter isotope ( U) is used in nuclear reactors and atomic bombs, whereas ( U) lacks the nuclear properties necessary for these applications. With the exception of hydrogen, which has different names for each of its isotopes, isotopes of elements are identified by their mass numbers. Thus, the two common isotopes of uranium are called uranium-235 and uranium-238. A list of the stable and radioactive isotopes for the first 10 elements is given in Appendix 4. 

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