NUCLEAR SCIENCE AND TECHNOLOGY

The Atom
Atoms are the smallest units of matter that have all the characteristics of an element. All matter (solid, fluid or gaseous) consists of elements.For example, an iron atom is the smallest unit of iron that has all the characteristics of the element iron. A helium atom (right) is the smallest unit of helium that has all the characteristics of the element helium.Atoms are the building blocks of everything in the universe.
NUCLEAR TECHNOLOGY
Nuclear technology is technology that involves the reactions of atomic nuclei. It has found applications from smoke detectors to nuclear reactors, and from gun sights to nuclear weapons. There is a great deal of public concern about its possible implications, and every application of nuclear technology is reviewed with care.[edit] DiscoveryIn 1896, Henri Becquerel was investigating phosphorescence in uranium salts when he discovered a new phenomenon which came to be called radioactivity.[1] He, Pierre Curie and Marie Curie began investigating the phenomenon. In the process they isolated the element radium, which is highly radioactive. They discovered that radioactive materials produce intense, penetrating rays of several distinct sorts, which they called alpha rays, beta rays and gamma rays. Some of these kinds of radiation could pass through ordinary matter, and all of them could cause damage in large amounts - all the early researchers received various radiation burns, much like sunburn, and thought little of it.The new phenomenon of radioactivity was seized upon by the manufacturers of quack medicine (as had the discoveries of electricity and magnetism, earlier), and any number of patent medicines and treatments involving radioactivity were put forward. Gradually it came to be realized that the radiation produced by radioactive decay was ionizing radiation, and that quantities too small to burn presented a severe long-term hazard. Many of the scientists working on radioactivity died of cancer as a result of their exposure. Radioactive patent medicines mostly disappeared, but other applications of radioactive materials persisted, such as the use of radium salts to produce glowing dials on meters.As the atom came to be better understood, the nature of radioactivity became clearer; some atomic nuclei are unstable, and can decay releasing energy in the form of gamma rays (high-energy photons), alpha particles (a pair of protons and a pair of neutrons) and beta particles, high-energy electrons.[edit] Nuclear fissionRadioactivity is generally a slow and difficult process to control, and is unsuited to building a weapon. However, other nuclear reactions are possible. In particular, a sufficiently unstable nucleus can undergo nuclear fission, breaking into two smaller nuclei and releasing energy and some fast neutrons. This neutron could, if captured by another nucleus, cause that nucleus to undergo fission as well. The process could then continue in a nuclear chain reaction. Such a chain reaction could release a vast amount of energy in a short amount of time. When discovered on the eve of World War II, it led multiple countries to begin programs investigating the possibility of constructing an atomic bomb—a weapon which utilized fission reactions to generate far more energy than could be created with chemical explosives. The Manhattan Project, run by the United States with the help of the United Kingdom and Canada, developed multiple fission weapons which were used against Japan in 1945. During the project, the first fission reactors were developed as well, though they were primarily for weapons manufacture and did not generate power.[edit] Nuclear fusionMain article: Timeline of nuclear fusionNuclear fusion technology was initially pursued only in theoretical stages during World War II, when scientists on the Manhattan Project (led by Edward Teller) investigated the possibility of using the great power of a fission reaction to ignite fusion reactions. It took until 1952 for the first full detonation of a hydrogen bomb to take place, so-called because it utilized reactions between deuterium and tritium, isotopes of hydrogen. Fusion reactions are much more energetic per unit mass of fusion material, but it is much more difficult to ignite a chain reaction than is fission.Research into the possibilities of using nuclear fusion for civilian power generation was begun during the 1940s as well. Technical and theoretical difficulties have hindered the development of working civilian fusion technology, though research continues to this day around the world.[edit] Nuclear WeaponsThe design of a nuclear weapon is more complicated than it might seem; it is quite difficult to ensure that such a chain reaction consumes a significant fraction of the fuel before the device flies apart. The construction of a nuclear weapon is also more difficult than it might seem, as no naturally occurring substance is sufficiently unstable for this process to occur. One isotope of uranium, namely uranium-235, is naturally occurring and sufficiently unstable, but it is always found mixed with the more stable isotope uranium-238. Thus a complicated and difficult process of isotope separation must be performed to obtain uranium-235. Alternatively, the element plutonium possesses an isotope that is sufficiently unstable for this process to be usable. Plutonium does not occur naturally, so it must be manufactured in a nuclear reactor. Ultimately, the Manhattan Project manufactured nuclear weapons based on each of these.The first atomic bomb was detonated in a test code-named "Trinity", near Alamogordo on July 16, 1945. After much debate on the morality of using such a horrifying weapon, two bombs were dropped on the Japanese cities Hiroshima and Nagasaki, and the Japanese surrender followed shortly.Several nations began nuclear weapons programs, developing ever more destructive bombs in an arms race to obtain what many called a nuclear deterrent. Nuclear weapons are the most destructive weapons known - the archetypal weapons of mass destruction. Throughout the Cold War, the opposing powers had huge nuclear arsenals, sufficient to kill hundreds of millions of people. Generations of people grew up under the shadow of nuclear devastation.However, the tremendous energy release in the detonation of a nuclear weapon also suggested the possibility of a new energy source.[edit] Nuclear PowerMain article: Nuclear powerCommercial nuclear power began in the early 1950s in the US, UK, and Soviet Union. The first commercial reactors were heavily based on either research reactors or military reactors. The first commercial nuclear reactor to go online in the US was the Shippingport Atomic Power Station in Western Pennsylvania.Some countries have banned all forms of nuclear power.[citation needed][edit] Types of nuclear reactionThis section may require cleanup to meet Wikipedia's quality standards.Please improve this article if you can. (August 2007)Most natural nuclear reactions fall under the heading of radioactive decay, where a nucleus is unstable and decays after a random interval. The most common processes by which this can occur are alpha decay, beta decay, and gamma decay. Under suitable circumstances, a large unstable nucleus can break into two smaller nuclei, undergoing nuclear fission.If these neutrons are captured by a suitable nucleus, they can trigger fission as well, leading to a chain reaction. A mass of radioactive material large enough (and in a suitable configuration) is called a critical mass. When a neutron is captured by a suitable nucleus, fission may occur immediately, or the nucleus may persist in an unstable state for a short time. If there are enough immediate decays to carry on the chain reaction, the mass is said to be prompt critical, and the energy release will grow rapidly and uncontrollably, usually leading to an explosion. However, if the mass is critical only when the delayed neutrons are included, the reaction can be controlled, for example by the introduction or removal of neutron absorbers. This is what allows nuclear reactors to be built. Fast neutrons are not easily captured by nuclei; they must be slowed (slow neutrons), generally by collision with the nuclei of a neutron moderator, before they can be easily captured.If nuclei are forced to collide, they can undergo nuclear fusion. This process may release or absorb energy. When the resulting nucleus is lighter than that of iron, energy is normally released; when the nucleus is heavier than that of iron, energy is generally absorbed. This process of fusion occurs in stars, and results in the formation, in stellar nucleosynthesis, of the light elements, from lithium to calcium, as well as some formation of the heavy elements, beyond Iron and Nickel, which cannot be created by nuclear fusion, via neutron capture - the S-process. The remaining abundance of heavy elements - from Nickel to Uranium and beyond - is due to supernova nucleosynthesis, the R-process. Of course, these natural processes of astrophysics are not examples of nuclear technology. Because of the very strong repulsion of nuclei, fusion is difficult to achieve in a controlled fashion. Hydrogen bombs obtain their enormous destructive power from fusion, but obtaining controlled fusion power has so far proved elusive. Controlled fusion can be achieved in particle accelerators; this is how many synthetic elements were produced. The Farnsworth-Hirsch Fusor is a device which can produce controlled fusion (and which can be built as a high-school science project), albeit at a net energy loss. It is sold commercially as a neutron source.The vast majority of everyday phenomena do not involve nuclear reactions. Most everyday phenomena only involve gravity and electromagnetism. Of the fundamental forces of nature, they are not the strongest, but the other two, the strong nuclear force and the weak nuclear force are essentially short-range forces so they do not play a role outside the atomic nucleus. Atomic nuclei are generally kept apart because they contain positive electrical charges and therefore repel each other, so in ordinary circumstances they cannot meet.[edit] Nuclear Accidents[edit] Three Mile island Incident (1979)The Three Mile Island incident, which ironically occurred two weeks after the release of the disaster film The China Syndrome greatly impacted the public's perception of nuclear power. Many human factors engineering improvements were made to American power plants in the wake of Three Mile Island's partial meltdown.[2][edit] Chernobyl Accident (1986)The Chernobyl accident in 1986 further alarmed the public about nuclear power. While design differences between the RBMK reactor used at Chernobyl and most western reactors virtually eliminate the possibility of such an accident occurring outside of the former Soviet Union, it is only recently that the general public in the United States has started to embrace nuclear energy.[edit] Examples of Nuclear Technology[edit] Nuclear PowerFurther information: Nuclear PowerNuclear power is a type of nuclear technology involving the controlled use of nuclear fission to release energy for work including propulsion, heat, and the generation of electricity. Nuclear energy is produced by a controlled nuclear chain reaction which creates heat—and which is used to boil water, produce steam, and drive a steam turbine. The turbine can be used for mechanical work and also to generate electricity.Currently nuclear power is used to propel aircraft carriers, icebreakers and submarines; and provides approximately 15.7% of the world's electricity (in 2004). The risk of radiation and cost have prohibited use of nuclear power in transport ships.[3][edit] Medical ApplicationsImaging - medical and dental x-ray imagers use of Cobalt-60 or other x-ray sources. Technetium-99m is used, attached to organic molecules, as radioactive tracer in the human body, before being excreted by the kidneys. Positron emitting nulceotides are used for high resolution, short time span imaging in applications known as Positron emission tomography.[edit] Industrial applicationsOil and Gas Exploration- Nuclear well logging is used to help predict the commercial viability of new or existing wells. The technology involves the use of a neutron or gamma-ray source and a radiation detector which are lowered into boreholes to determine the properties of the surrounding rock such as porosity and lithography.[1]Road Construction - Nuclear moisture/density gauges are used to determine the density of soils, asphalt, and concrete. Typically a Cesium-137 source is used.[edit] Commercial applicationsAn ionization smoke detector includes a tiny mass of radioactive americium-241, which is a source of alpha radiation. Tritium is used with phosphor in rifle sights to increase nighttime firing accuracy. Luminescent exit signs use the same technology.[4][edit] Food Processing and AgricultureThe Radura logo, used to show a food has been treated with ionizing radiation.Food irradiation[5] is the process of exposing food to ionizing radiation in order to destroy microorganisms, bacteria, viruses, or insects that might be present in the food. Further applications include sprout inhibition, delay of ripening, increase of juice yield, and improvement of re-hydration. Irradiation is a more general term of deliberate exposure of materials to radiation to achieve a technical goal (in this context 'ionizing radiation' is implied). As such it is also used on non-food items, such as medical hardware, plastics, tubes for gas-pipelines, hoses for floor-heating, shrink-foils for food packaging, automobile parts, wires and cables (isolation), tires, and even gemstones. Compared to the amount of food irradiated, the volume of those every-day applications is huge but not noticed by the consumer.The genuine effect of processing food by ionizing radiation relates to damages to the DNA, the basic genetic information for life. Microorganisms can no longer proliferate and continue their malignant or pathogen activities. Spoilage causing micro-organisms cannot continue their activities. Insects do not survive or become incapable of proliferation. Plants cannot continue the natural ripening or aging process. All these effects are beneficial to the consumer and the food industry, likewise.[5]It should be noted that the amount of energy imparted for effective food irradiation is low compared to cooking the same; even at a typical dose of 10 kGy most food, which is (with regard to warming) physically equivalent to water, would warm by only about 2.5 °C.The speciality of processing food by ionizing radiation is the fact, that the energy density per atomic transition is very high, it can cleave molecules and induce ionization (hence the name) which cannot be achieved by mere heating. This is the reason for new beneficial effects, however at the same time, for new concerns. The treatment of solid food by ionizing radiation can provide an effect similar to heat pasteurization of liquids, such as milk. However, the use of the term, cold pasteurization, to describe irradiated foods is controversial, because pasteurization and irradiation are fundamentally different processes, although the intended end results can in some cases be similar.Nuclear EnergyThe sun and stars are seemingly inexhaustible sources of energy. That energy is the result of nuclear reactions, in which matter is converted to energy. We have been able to harness that mechanism and regularly use it to generate power. Presently, nuclear energy provides for approximately 16% of the world's electricity. Unlike the stars, the nuclear reactors that we have today work on the principle of nuclear fission. Scientists are working like madmen to make fusion reactors which have the potential of providing more energy with fewer disadvantages than fission reactors.ProductionChanges can occur in the structure of the nuclei of atoms. These changes are called nuclear reactions. Energy created in a nuclear reaction is called nuclear energy, or atomic energy.Nuclear energy is produced naturally and in man-made operations under human control.Naturally: Some nuclear energy is produced naturally. For example, the Sun and other stars make heat and light by nuclear reactions.Man-Made: Nuclear energy can be man-made too. Machines called nuclear reactors, parts of nuclear power plants, provide electricity for many cities. Man-made nuclear reactions also occur in the explosion of atomic and hydrogen bombs.Nuclear energy is produced in two different ways, in one, large nuclei are split to release energy. In the other method, small nuclei are combined to release energy.For a more detailed look at nuclear fission and nuclear fusion, consult the nuclear physics page.Nuclear Fission: In nuclear fission, the nuclei of atoms are split, causing energy to be released. The atomic bomb and nuclear reactors work by fission. The element uranium is the main fuel used to undergo nuclear fission to produce energy since it has many favorable properties. Uranium nuclei can be easily split by shooting neutrons at them. Also, once a uranium nucleus is split, multiple neutrons are released which are used to split other uranium nuclei. This phenomenon is known as a chain reaction.Fission of uranium 235 nucleus. Adapted from Nuclear Energy. Nuclear Waste*.Nuclear Fusion: In nuclear fusion, the nuclei of atoms are joined together, or fused. This happens only under very hot conditions. The Sun, like all other stars, creates heat and light through nuclear fusion. In the Sun, hydrogen nuclei fuse to make helium. The hydrogen bomb, humanity's most powerful and destructive weapon, also works by fusion. The heat required to start the fusion reaction is so great that an atomic bomb is used to provide it. Hydrogen nuclei fuse to form helium and in the process release huge amounts of energy thus producing a huge explosion.Milestones in the History of Nuclear EnergyAmore in depth and detailed history of nuclear energy is on the nuclear past page.December 2, 1942: The Nuclear Age began at the University of Chicago when Enrico Fermi made a chain reaction in a pile of uranium.August 6, 1945: The United States dropped an atomic bomb on Hiroshima, Japan, killing over 100,000.August 9, 1945: The United States dropped an atomic bomb on Nagasaki, Japan, killing over 40,000.November 1, 1952: The first large version of the hydrogen bomb (thousands of times more powerful than the atomic bomb) was exploded by the United States for testing purposes.February 21, 1956: The first major nuclear power plant opened in England.Advantages of Nuclear EnergyThe Earth has limited supplies of coal and oil. Nuclear power plants could still produce electricity after coal and oil become scarce.Nuclear power plants need less fuel than ones which burn fossil fuels. One ton of uranium produces more energy than is produced by several million tons of coal or several million barrels of oil.Coal and oil burning plants pollute the air. Well-operated nuclear power plants do not release contaminants into the environment.Disadvantages of Nuclear EnergyThe nations of the world now have more than enough nuclear bombs to kill every person on Earth. The two most powerful nations -- Russia and the United States -- have about 50,000 nuclear weapons between them. What if there were to be a nuclear war? What if terrorists got their hands on nuclear weapons? Or what if nuclear weapons were launched by accident?Nuclear explosions produce radiation. The nuclear radiation harms the cells of the body which can make people sick or even kill them. Illness can strike people years after their exposure to nuclear radiation.One possible type of reactor disaster is known as a meltdown. In such an accident, the fission reaction goes out of control, leading to a nuclear explosion and the emission of great amounts of radiation.In 1979, the cooling system failed at the Three Mile Island nuclear reactor near Harrisburg, Pennsylvania. Radiation leaked, forcing tens of thousands of people to flee. The problem was solved minutes before a total meltdown would have occurred. Fortunately, there were no deaths.In 1986, a much worse disaster struck Russia's Chernobyl nuclear power plant. In this incident, a large amount of radiation escaped from the reactor. Hundreds of thousands of people were exposed to the radiation. Several dozen died within a few days. In the years to come, thousands more may die of cancers induced by the radiation.Nuclear reactors also have waste disposal problems. Reactors produce nuclear waste products which emit dangerous radiation. Because they could kill people who touch them, they cannot be thrown away like ordinary garbage. Currently, many nuclear wastes are stored in special cooling pools at the nuclear reactors.The United States plans to move its nuclear waste to a remote underground dump by the year 2010.In 1957, at a dump site in Russia's Ural Mountains, several hundred miles from Moscow, buried nuclear wastes mysteriously exploded, killing dozens of people.Nuclear reactors only last for about forty to fifty years.The Future of Nuclear EnergySome people think that nuclear energy is here to stay and we must learn to live with it. Others say that we should get rid of all nuclear weapons and power plants. Both sides have their cases as there are advantages and disadvantages to nuclear energy. Still others have opinions that fall somewhere in between.What do you think we should do? After reviewing the pros and cons, it is up to you to formulate your own opinion. Read more about the politics of the issues or go to the forum to share your own opinions and see what others think.Nuclear power plant typesThe structure of a nuclear power plant in many aspects resembles to that of a conventional thermal power station, since in both cases the heat produced in the boiler (or reactor) is transported by some coolant and used to generate steam. The steam then goes to the blades of a turbine and by rotating it, the connected generator will produce electric energy. The steam goes to the condenser, where it condenses, i.e. becomes liquid again. The cooled down water afterwards gets back to the boiler or reactor, or in the case of PWRs to the steam generator.The great difference between a conventional and a nuclear power plant is how heat is produced. In a fossile plant, oil, gas or coal is fired in the boiler, which means that the chemical energy of the fuel is converted into heat. In a nuclear power plant, however, energy that comes from fission reactions is utilized.Several nuclear power plant (NPP) types are used for energy generation in the world. The different types are usually classified based on the main features of the reactor applied in them. The most widespread power plant reactor types are:Light water reactors: both the moderator and coolant are light water (H2O). To this category belong the pressurized water reactors (PWR) and boiling water reactors (BWR).Heavy water reactors (CANDU): both the coolant and moderator are heavy water (D2O).Graphite moderated reactors: in this category there are gas cooled reactors (GCR) and light water cooled reactors (RBMK).Exotic reactors (fast breeder reactors and other experimental installations).New generation reactors: reactors of the future.Nuclear power plant typesThe great difference between a conventional and a nuclear power plant is how heat is produced. In a fossile plant, oil, gas or coal is fired in the boiler, which means that the chemical energy of the fuel is converted into heat. In a nuclear power plant, however, energy that comes from fission reactions is utilized.Several nuclear power plant (NPP) types are used for energy generation in the world. The different types are usually classified based on the main features of the reactor applied in them. The most widespread power plant reactor types are:Light water reactors: both the moderator and coolant are light water (H2O). To this category belong the pressurized water reactors (PWR) and boiling water reactors (BWR).Heavy water reactors (CANDU): both the coolant and moderator are heavy water (D2O).Graphite moderated reactors: in this category there are gas cooled reactors (GCR) and light water cooled reactors (RBMK).Exotic reactors (fast breeder reactors and other experimental installations).New generation reactors: reactors of the future.