Archive for the ‘NUCLEAR ENERGY’ Tag

SPECTRUM AND SPECTROSCOPE (Part 2 of 3)   Leave a comment

 

Study of the lines in various spectra has helped build the modern theory of matter. Soon after Bunsen and Kirchhoff developed the use of spectral lines as a means of chemical analysis, scientists thought that the various lines were given off by atoms vibrating at different rates under the stimulus of heat. They believed that the faster vibrations resulted in the shorter waves that caused lines to appear toward the violet end of the spectrum.

 

Rydberg, Johannes Robert (1854-1919), Swedish physicist; worked on the spectrum.

 

In 1885 Johann Jakob Balmer (1825-98) discovered through experimentation that the various rates of vibration in a mass of glowing hydrogen bore a simple mathematical relation to each other. This indicated that some one type of “mechanism” was at work at varying rates within the hydrogen atom, giving off the different wavelengths. Balmer could not guess what this “mechanism” might be, however. Then Johannes Robert Rydberg (1854-1919) introduced further information on this subject and developed a formula named for him that described many more observed relations; but he also did not know what it was within the atom that vibrated. Finally, the answer came in 1913 from Niels Bohr (1885-1962), the renowned Danish physicist.

 

Bohr’s theory, built largely upon knowledge from the study of radioactivity, held that the hydrogen atom consisted of an electron revolving like a planet around a central nucleus, or “sun.” Bohr believed further that as an atom absorbed energy by being heated, for example this orbit would enlarge by definite amounts, each enlargement representing the absorption of one quantum, or “packet,” of energy. When energy was emitted, as in the form of light, the electron would fall by steps into inner orbits, and the frequency of the light would depend upon how many orbits were traversed. If the electron fell inward by one orbit, the “energy splash” resulting from this would travel outward as light of a certain frequency. If it fell inward by two orbits, light of a different frequency would go forth. The collection of lines given by hydrogen in a spectroscope sums up these actions taking place in all the hydrogen atoms present. Furthermore, by using the Planck constant (the fundamental measurement of a quantum) and electrical factors in a formula of the Rydberg type, Bohr was able to reduce his whole explanation to terms of electrical force. Thus the spectrum of hydrogen was explained as the product of electrical forces within the atom, and the spectroscope became useful for studying the structure of matter.

 

Another significant discovery was that X rays could be made to give spectra just as visible light did. This was done by causing a beam of X rays to fall upon a crystal. The short rays of the X rays were diffracted in a pattern that revealed the arrangement of atoms in the crystal.

SPECTRUM AND SPECTROSCOPE (Part 3 of 3)   Leave a comment

Moseley, Henry Gwyn-Jeffreys (1887-1915), British physicist, born in Weymouth, England; gave his name to the Moseley number.

In 1913 and 1914 the English physicist H.G.J. Moseley (1887-1915) announced the discovery of far-reaching relations among X rays produced from the surfaces of different metals by the impact of electrons. He found that each metal gives certain groups of X-ray lines, corresponding to certain frequencies. As he passed from a lighter to a heavier metal, each successive element showed lines of higher frequencies. Moseley reasoned that this was not due to increasing atomic weight, since several substances of different atomic weights showed the same spectra. It must have been due to a regular increase in the number of orbiting electrons, corresponding to the atomic number, of the atoms of the metals. Moseley’s work provided the basis for the modern periodic classification of elements.

Modern Applications

Spectroscopes are used in almost every technical field, especially for identifying constituents and processes in any source that emits light. In some industries many similar samples must be analysed quickly and simultaneously for their light-absorbing characteristics. A physician may have several hundred samples of blood serum to analyse in a short period of time. Fortunately, fully automated analytical spectroscopes are available. New techniques of analysing samples based on how they absorb radiation to differing extents have given scientists new ways to determine a substance’s properties. Infra-red spectroscopy, ultraviolet spectroscopy, and nuclear magnetic resonance spectroscopy are the most commonly used of such techniques.

In the 20th century, scientists discovered that all atomic particles behave as if they had wavelengths much like those of light waves. Spectroscopes were used to study these particles. The study of the various elementary particles themselves is divided into baryon and meson spectroscopy, and elementary-particle spectrometers are used for such studies. One of the accomplishments of neutron spectroscopy, another field, was the plotting of the structure of large complex molecules like those of DNA and RNA, the basic materials of heredity. Furthermore, spectroscopes are used to measure temperatures in controlled thermonuclear fusion.

ENVIRONMENTAL POLLUTION (Part 2 of 2).   1 comment

Water Pollution

Since the beginning of civilization, water has been used to carry away unwanted refuse. Rivers, streams, canals, lakes, and oceans are currently used as receptacles for every imaginable kind of pollution. Water has the capacity to break down or dissolve many materials, especially organic compounds, which decompose during prolonged contact with bacteria and enzymes. Waste materials that can eventually decompose in this way are called biodegradable. They are less of a long-term threat to the environment than are more persistent pollutants such as metals, plastics, and some chlorinated hydrocarbons. These substances remain in the water and can make it poisonous for most forms of life. Even biodegradable pollutants can damage a water supply for long periods of time. As any form of contamination accumulates, life within the water starts to suffer. Lakes are especially vulnerable to pollution because they cannot cleanse themselves as rapidly as rivers or oceans.

A common kind of water pollution is the effect caused by heavy concentrations of nitrogen and phosphorus, which are used by plants for growth. The widespread use of agricultural fertilizers and household detergents containing these elements has added large amounts of plant nutrients to many bodies of water. In large quantities, nitrogen and phosphorus cause tiny water algae to bloom, or grow rapidly. When the algae die, oxygen is needed to decompose them. This creates an oxygen deficiency in the water, which causes the death of many aquatic animals. Plant life soon reduces the amount of open water. These events speed up the process of eutrophication, the ageing and eventual drying up of a lake.

Sedimentation also pollutes water. It is the result of poor soil conservation practices. Sediment fills water-supply reservoirs and fouls power turbines and irrigation pumps. It also diminishes the amount of sunlight that can penetrate the water. In the absence of sufficient sunlight, the aquatic plants that normally furnish the water with oxygen fail to grow.

Factories sometimes turn waterways into open sewers by dumping oils, toxic chemicals, and other harmful industrial wastes into them. In mining and oil-drilling operations, corrosive acid wastes are poured into the water. In recent years, municipal waste treatment plants have been built to contend with water contamination. Some towns, however, still foul streams by pouring raw sewage into them. Septic tanks and cesspools, used where sewers are not available, may also pollute the groundwater and adjacent streams, sometimes with disease-causing organisms. Even the purified effluent from sewage plants can cause water pollution if it contains high concentrations of nitrogen and phosphorus. Farm fertilizers in some regions fill groundwater with nitrates, making the water unfit to drink. Agricultural run-off containing dangerous pesticides and the oil, grime, and chemicals used to melt ice from city streets also pollute waterways.

Land and Soil Pollution

In order to sustain the continually growing human population, current agricultural methods are designed to maximize yields from crop lands In many areas, the overuse of land results in the erosion of topsoil. This soil erosion, in turn, causes the over-silting or sedimentation of rivers and streams.

One of the most hazardous forms of pollution comes from agricultural pesticides. These chemicals are designed to deter or kill insects, weeds, fungi, or rodents that pose a threat to crops. When airborne pesticides drift with the wind or become absorbed into the fruits and vegetables they are meant to protect, they can become a source of many illnesses, including cancer and birth defects.

Pesticides are often designed to withstand rain, which means they are not always water-soluble, and therefore they may persist in the environment for long periods of time. Some pests have developed a genetic resistance to these chemicals, forcing farmers to increase the amounts or types of pesticide.

The pesticide DDT provides the best-known example of the dangers of introducing synthetic chemical compounds into the environment. Chemically a chlorinated hydrocarbon, DDT was widely used for many years after World War II. At first it was highly regarded because it reduced the incidence of malaria throughout the world. Then, evidence began to show that DDT might be doing more harm than good. DDT, like other chemically stable pesticides, is not readily biodegradable. It has been found in the tissues of every organism tested for its presence. DDT is now known to affect biological activities. It reduces the rate of photosynthesis in marine phytoplankton, organisms that form the basis of most ocean food chains.

Although DDT has been banned in the United States and most other countries, it is still manufactured and used in some parts of the world. Many other pesticides also have been banned. Thousands of pesticides remain in use and, in some cases, their agricultural value may balance out their risks.

Some urban areas are beginning to experience a serious problem regarding the disposal of garbage and hazardous wastes, such as solvents and industrial dyes and inks. In many areas landfill sites are approaching their full capacity and many municipalities are turning to incineration as a solution. Giant high-temperature incinerators have become another source of air pollution, however, because incineration ashes sometimes contain very high concentrations of metals as well as dioxins, a dangerous family of chemical poisons.

One answer to the garbage problem is recycling. Some towns have passed ordinances that encourage or require residents to separate glass and aluminium cans and bottles from other refuse so that these substances can be melted down and reused. Although lightweight steel, cardboard, and paper are also economically recyclable, most industries and cities still burn or bury large amounts of scrap metal and paper products every day.

Radioactive Pollutants

Cosmic rays, highly penetrating radiations reaching the Earth from outer space.

Radioactivity has always been part of the natural environment. An example of natural radioactivity is the cosmic radiation that constantly strikes the Earth. This so-called background radiation has little effect on most people. Some scientists are concerned, however, that humans have introduced a considerable amount of additional radiation into the environment.

Since the first atomic bomb was dropped on Hiroshima, Japan, on Aug. 6, 1945, there has been an increased awareness of the environmental threat posed by nuclear weapons and radioactive fallout. Many scientists are concerned about the long-term environmental impacts of full-scale nuclear war. Some suggest that the large amounts of smoke and dust thrown into the atmosphere during a nuclear explosion would block out the sun’s light and heat, causing global temperatures to drop.

Even the testing of nuclear weapons directly affects the environment. Such tests are rarely conducted above ground or in the ocean. International concern over the effects of these tests led the United States, Great Britain, and the Soviet Union to sign the Nuclear Test-Ban Treaty in 1963.

On April 26, 1986, the Chernobyl nuclear power plant in the Soviet Union malfunctioned creating the worst peacetime nuclear disaster. Many details of the Chernobyl accident remain undisclosed, but it is known that the radioactive core of the power plant became exposed, and there was a partial meltdown, releasing large amounts of radioactive materials. Because the medical effects of exposure to nuclear radiation can take years to become apparent, it is not yet known how many additional cases of cancer, birth defects, and skin disease will have been caused by the Chernobyl accident.

Another immediate environmental problem is the disposal of nuclear wastes. Some radioactive substances have a half-life of more than 10,000 years, which means they remain radioactive and highly dangerous for many thousands of years. In nuclear physics, a half-life is the period of time required for the disintegration of half of the atoms in a sample of a radioactive substance. Science has not yet found a safe method of permanent disposal of high level radioactive wastes. Even temporary storage of these wastes is a dangerous and expensive problem. Experiments are under way to investigate the possible use of salt mines several thousand feet below the surface of the Earth as repositories for spent nuclear fuel rods and similar highly radioactive substances.

Thermal, or Heat, Pollution

While the concept of heat as a pollutant may seem improbable on a cold winter day, at any time of year an increase in water temperature has an effect on water life. Heat can be unnaturally added to streams and lakes in a number of ways. One is to cut down a forest completely. The brooks and streams that flowed through it are then exposed to the sun. Their temperatures begin to rise. As they flow into larger bodies of water, these in turn are warmed. This can kill fish and other water animals incapable of tolerating the higher temperatures.

Heat pollution is a consequence of the rising energy needs of man. As electric power plants burn fossil fuels or nuclear fuel to provide this energy, they release considerable amounts of heat. Power plants are usually located near bodies of water, which the plants use for heat-dissipation purposes. Some stretches of the Hudson River in New York no longer freeze in winter because of the flow of hot water into the river from adjacent power plants. Living things especially such cold-blooded animals as fish are very sensitive to even small changes in the average temperature. Because of the added heat in waters affected by power plants, many aquatic habitats may be undergoing drastic change. In some instances, the warmer water may cause fish eggs to hatch before their natural food supply is available. In other instances, it may prevent fish eggs from hatching at all.

In addition, a very small rise in the average temperature of the Earth’s surface could produce profound climatic changes. Some experts believe that it would cause the Greenland and Antarctic ice caps to melt, raising ocean levels and inundating large areas of land.

Average worldwide temperatures can be affected when the products of combustion carbon monoxide, water vapour, and carbon dioxide are emitted into the air, especially at high altitudes. Since the normal level of carbon dioxide in the air is quite small, any significant addition is a potential threat. Although solar energy on its way to the Earth’s surface easily passes through layers of carbon dioxide, some of the heat escaping from the Earth would be absorbed by increased amounts of atmospheric carbon dioxide, much as heat is trapped in a greenhouse. A worldwide greenhouse effect of this type might produce a dangerously warmer world. Since the late 19th century, the average global temperature has increased between 0.54°F and 1.08°F (0.3°C and 0.6°C). Internationally, 1990 was the hottest year on record since official weather records first started being kept by the British in about 1860.

Noise Pollution

The hearing apparatus of living things is sensitive to certain frequency ranges and sound intensities. Sound intensities are measured in decibels. For example, a clap of thunder has an intensity of about 100 decibels. A sound at or above the 120-decibel level is painful and can injure the ear. Noise pollution is becoming an unpleasant fact of life in cities, where the combination of sounds from traffic and building construction reverberates among high-rise buildings, creating a constant din.

In addition, the intense volume at which some popular music, especially heavy metal rock music, is played has resulted in the loss of some or all of the hearing of a few musicians and members of their audiences. There is some evidence that extreme levels of noise can produce other deleterious effects on human health and on work performance.

Efforts to Halt Pollution

The solution of some pollution problems requires cooperation at regional, national, and international levels. For example, some of the acid rain that falls in Canada is caused by smokestacks of coal-burning power plants in the United States. Thus, rejuvenating the lakes of eastern Canada requires the cooperation of electric utilities in Indiana and Ohio.

Greenpeace Foundation, international organization for the protection of the environment.

In the United States laws have been passed to regulate the discharge of pollutants into the environment. The Environmental Protection Agency (EPA), which was formed through the National Environmental Policy Act (NEPA) of 1969, oversees most federal anti pollution activity. The National Environmental Policy Act also mandated the use of environmental impact statements, which require that businesses or governments examine alternatives and acknowledge the possible harmful effects of such activities as opening new factories, building dams, and developing new oil wells. With the advent of massive oil spills from supertankers, the washing up of medical wastes on shores in New York and New Jersey, and an increased build-up of toxic wastes, such international organizations as Greenpeace have become ever more dedicated to preventing environmental abuses and heightening public awareness of environmental issues.

The Clean Air Act, the Safe Drinking Water Act, and the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (known as Super fund) are among the laws that set standards for healthy air and water and the safe disposal of toxic chemicals. In 1990 President George Bush signed the Clean Air Act of 1990, the second amending legislation since the original Clean Air Act of 1970. The new law called for reductions in emissions of sulphur dioxide and nitrogen oxide by half, carbon monoxide from vehicles by 70 percent, and other emissions by 20 percent. The number of toxic chemicals monitored by the EPA would increase from 7 to about 250, and industry would be required to control their waste release by means of the best technology available. In the same year, the California Air Resources Board introduced the strictest vehicle-emission controls in the world. By 2003 the hydrocarbon emission of all new cars sold in California would have to be at least 70 percent less than that of 1993 models, and by 1998, 2 percent of all cars (rising to 10 percent by 2003) would have to release no harmful emissions at all. Several North-eastern states followed suit by introducing similar, though slightly less severe, controls.

Assisted by John H. Thomas, professor of biology at Stanford University, and Paul J. Allen, Director of Communications at the Natural Resources Defense Council, Washington, D.C.

BIBLIOGRAPHY FOR ENVIRONMENTAL POLLUTION

Caplan, Ruth. Our Earth, Ourselves (Bantam, 1990).

Carson, Rachel. Silent Spring (Houghton, 1987).

Luoma, Jon. The Air Around Us (Acid Rain Foundation, 1989).

Mott, Lawrie and others. Pesticide Alert (Sierra Club and National Resource Defense Council, 1988).

Newton, David. Taking a Stand Against Pollution (Watts, 1990).

Thackray, Sue. Looking at Pollution (David and Charles, 1987).

Trager, Oliver, ed. Our Poisoned Planet: Can We Save It? (Facts on File, 1989).

Tripathi, A.K. and Pandey, S.N. Water Pollution (South Asia Books, 1990).