Nuclear reactor

The invention: 



The first nuclear reactor to produce substantial

quantities of plutonium, making it practical to produce usable

amounts of energy from a chain reaction.



The people behind the invention:



Enrico Fermi (1901-1954), an American physicist

Martin D. Whitaker (1902-1960), the first director of Oak Ridge

National Laboratory

Eugene Paul Wigner (1902-1995), the director of research and

development at Oak Ridge









The Technology to End a War



The construction of the nuclear reactor at Oak Ridge National

Laboratory in 1943 was a vital part of the Manhattan Project, the effort

by the United States during World War II (1939-1945) to develop

an atomic bomb. The successful operation of that reactor

was a major achievement not only for the project itself but also for

the general development and application of nuclear technology.

The first director of the Oak Ridge National Laboratory was Martin

D. Whitaker; the director of research and development was Eugene

Paul Wigner.

The nucleus of an atom is made up of protons and neutrons. “Fission”

is the process by which the nucleus of certain elements is split

in two by a neutron from some material that emits an occasional

neutron naturally. When an atom splits, two things happen: A tremendous

amount of thermal energy is released, and two or three

neutrons, on the average, escape from the nucleus. If all the atoms in

a kilogram of “uranium 235” were to fission, they would produce as

much heat energy as the burning of 3 million kilograms of coal. The

neutrons that are released are important, because if at least one of

them hits another atom and causes it to fission (and thus to release

more energy and more neutrons), the process will continue. It will

become a self-sustaining chain reaction that will produce a continuing

supply of heat.

Inside a reactor, a nuclear chain reaction is controlled so that it

proceeds relatively slowly. The most familiar use for the heat thus

released is to boil water and make steam to turn the turbine generators

that produce electricity to serve industrial, commercial, and

residential needs. The fissioning process in a weapon, however, proceeds

very rapidly, so that all the energy in the atoms is produced

and released virtually at once. The first application of nuclear technology,

which used a rapid chain reaction, was to produce the two

atomic bombs that ended World War II.





Breeding Bomb Fuel



The work that began at Oak Ridge in 1943 was made possible by a

major event that took place in 1942. At the University of Chicago,

Enrico Fermi had demonstrated for the first time that it was possible to

achieve a self-sustaining atomic chain reaction. More important, the reaction

could be controlled: It could be started up, it could generate heat

and sufficient neutrons to keep itself going, and it could be turned off.

That first chain reaction was very slow, and it generated very little heat;

but it demonstrated that controlled fission was possible.

Any heat-producing nuclear reaction is an energy conversion

process that requires fuel. There is only one readily fissionable element

that occurs naturally and can be used as fuel. It is a form of

uranium called uranium 235. It makes up less than 1 percent of all

naturally occurring uranium. The remainder is uranium 238, which

does not fission readily. Even uranium 235, however, must be enriched

before it can be used as fuel.

The process of enrichment increases the concentration of uranium

235 sufficiently for a chain reaction to occur. Enriched uranium is used

to fuel the reactors used by electric utilities. Also, the much more plentiful

uranium 238 can be converted into plutonium 239, a form of the

human-made element plutonium, which does fission readily. That

conversion process is the way fuel is produced for a nuclear weapon.

Therefore, the major objective of the Oak Ridge effort was to develop a

pilot operation for separating plutonium from the uranium in which it

was produced. Large-scale plutonium production, which had never

been attempted before, eventually would be done at the Hanford Engineer

Works in Washington. First, however, plutonium had to be pro-

duced successfully on a small scale at Oak Ridge.

The reactor was started up on November 4, 1943. By March 1,

1944, the Oak Ridge laboratory had produced several grams of plutonium.

The material was sent to the Los Alamos laboratory in New

Mexico for testing. By July, 1944, the reactor operated at four times

its original power level. By the end of that year, however, plutonium

production at Oak Ridge had ceased, and the reactor thereafter was

used principally to produce radioisotopes for physical and biological

research and for medical treatment. Ultimately, the Hanford Engineer

Works’ reactors produced the plutonium for the bomb that

was dropped on Nagasaki, Japan, on August 9, 1945.

The original objectives for which Oak Ridge had been built had

been achieved, and subsequent activity at the facility was directed

toward peacetime missions that included basic studies of the structure

of matter.



Impact



The most immediate impact of the work done at Oak Ridge was

its contribution to ending World War II. When the atomic bombs

were dropped, the war ended, and the United States emerged intact.

The immediate and long-range devastation to the people of Japan,

however, opened the public’s eyes to the almost unimaginable

death and destruction that could be caused by a nuclear war. Fears

of such a war remain to this day, especially as more and more nations

develop the technology to build nuclear weapons.

On the other hand, great contributions to human civilization

have resulted from the development of nuclear energy. Electric

power generation, nuclear medicine, spacecraft power, and ship

propulsion have all profited from the pioneering efforts at the Oak

Ridge National Laboratory. Currently, the primary use of nuclear

energy is to produce electric power. Handled properly, nuclear energy

may help to solve the pollution problems caused by the burning

of fossil fuels.



See also Breeder reactor; Compressed-air-accumulating powerplant; Fuel cell;

Geothermal power; Heat pump; Nuclear power plant; Solar thermal engine; Nuclear reactor

Nuclear power plant

The invention: 



The first full-scale commercial nuclear power plant,
which gave birth to the nuclear power industry.

 







The people behind the invention:



Enrico Fermi (1901-1954), an Italian American physicist who

won the 1938 Nobel Prize in Physics

Otto Hahn (1879-1968), a German physical chemist who won the

1944 Nobel Prize in Chemistry

Lise Meitner (1878-1968), an Austrian Swedish physicist

Hyman G. Rickover (1898-1986), a Polish American naval officer









Discovering Fission



Nuclear fission involves the splitting of an atomic nucleus, leading

to the release of large amounts of energy. Nuclear fission was

discovered in Germany in 1938 by Otto Hahn after he had bombarded

uranium with neutrons and observed traces of radioactive

barium. When Hahn’s former associate, Lise Meitner, heard of this,

she realized that the neutrons may have split the uranium nuclei

(each of which holds 92 protons) into two smaller nuclei to produce

barium (56 protons) and krypton (36 protons). Meitner and her

nephew, Otto Robert Frisch, were able to calculate the enormous energy

that would be released in this type of reaction. They published

their results early in 1939.

Nuclear fission was quickly verified in several laboratories, and

the Danish physicist Niels Bohr soon demonstrated that the rare uranium

235 (U-235) isotope is much more likely to fission than the common

uranium 238 (U-238) isotope, which makes up 99.3 percent of

natural uranium. It was also recognized that fission would produce

additional neutrons that could cause new fissions, producing even

more neutrons and thus creating a self-sustaining chain reaction. In

this process, the fissioning of one gram of U-235 would release about

as much energy as the burning of three million tons of coal.

The first controlled chain reaction was demonstrated on December

2, 1942, in a nuclear reactor at the University of Chicago, under

 the leadership of Enrico Fermi. He used a graphite moderator to

slow the neutrons by collisions with carbon atoms. “Critical mass”

was achieved when the mass of graphite and uranium assembled

was large enough that the number of neutrons not escaping from

the pile would be sufficient to sustain a U-235 chain reaction. Cadmium

control rods could be inserted to absorb neutrons and slow

the reaction.

It was also recognized that the U-238 in the reactor would absorb

accelerated neutrons to produce the new element plutonium, which

is also fissionable. During World War II (1939-1945), large reactors

were built to “breed” plutonium, which was easier to separate than

U-235. An experimental breeder reactor at Arco, Idaho, was the first

to use the energy of nuclear fission to produce a small amount of

electricity (about 100 watts) on December 20, 1951.





Nuclear Electricity



Power reactors designed to produce substantial amounts of

electricity use the heat generated by fission to produce steam or

hot gas to drive a turbine connected to an ordinary electric generator.

The first power reactor design to be developed in the United

States was the pressurized water reactor (PWR). In the PWR, water

under high pressure is used both as the moderator and as the coolant.

After circulating through the reactor core, the hot pressurized

water flows through a heat exchanger to produce steam. Reactors

moderated by “heavy water” (in which the hydrogen in the water

is replaced with deuterium, which contains an extra neutron) can

operate with natural uranium.

The pressurized water system was used in the first reactor to

produce substantial amounts of power, the experimental Mark I

reactor. It was started up on May 31, 1953, at the Idaho National

Engineering Laboratory. The Mark I became the prototype for the

reactor used in the first nuclear-powered submarine. Under the

leadership of Hyman G. Rickover, who was head of the Division of

Naval Reactors of the Atomic Energy Commission (AEC), Westinghouse

Electric Corporation was engaged to build a PWR system

to power the submarine USS Nautilus. It began sea trials in January

of 1955 and ran for two years before refueling.

In the meantime, the first experimental nuclear power plant for

generating electricity was completed in the Soviet Union in June of

1954, under the direction of the Soviet physicist Igor Kurchatov. It

produced 5 megawatts of electric power. The first full-scale nuclear

power plant was built in England under the direction of the British

nuclear engineer Sir Christopher Hinton. It began producing about

90 megawatts of electric power in October, 1956.

 On December 2, 1957, on the fifteenth anniversary of the first controlled

nuclear chain reaction, the Shippingport Atomic Power Station

in Shippingport, Pennsylvania, became the first full-scale commercial

nuclear power plant in the United States. It produced about

60 megawatts of electric power for the Duquesne Light Company until

1964, when its reactor core was replaced, increasing its power to

100 megawatts with a maximum capacity of 150 megawatts.





Consequences



The opening of the Shippingport Atomic Power Station marked

the beginning of the nuclear power industry in the United States,

with all of its glowing promise and eventual problems. It was predicted

that electrical energy would become too cheap to meter. The

AEC hoped to encourage the participation of industry, with government

support limited to research and development. They encouraged

a variety of reactor types in the hope of extending technical

knowledge.

The Dresden Nuclear Power Station, completed by Commonwealth

Edison in September, 1959, at Morris, Illinois, near Chicago,

was the first full-scale privately financed nuclear power station in

the United States. By 1973, forty-two plants were in operation producing

26,000 megawatts, fifty more were under construction, and

about one hundred were on order. Industry officials predicted that

50 percent of the nation’s electric power would be nuclear by the

end of the twentieth century.

The promise of nuclear energy has not been completely fulfilled.

Growing concerns about safety and waste disposal have led to increased

efforts to delay or block the construction of new plants. The

cost of nuclear plants rose as legal delays and inflation pushed costs

higher, so that many in the planning stages could no longer be competitive.

The 1979 Three Mile Island accident in Pennsylvania and

the much more serious 1986 Chernobyl accident in the Soviet Union

increased concerns about the safety of nuclear power. Nevertheless,

by 1986, more than one hundred nuclear power plants were operating

in the United States, producing about 60,000 megawatts of

power. More than three hundred reactors in twenty-five countries

provide about 200,000 megawatts of electric power worldwide.

 Many believe that, properly controlled, nuclear energy offers a

clean-energy solution to the problem of environmental pollution.





See also : Breeder reactor; Compressed-air-accumulating power

plant; Fuel cell; Geothermal power; Nuclear reactor; Solar thermal

engine; Nuclear power plant




 Further Reading :

Nuclear magnetic resonance

The invention: Procedure that uses hydrogen atoms in the human body, strong electromagnets, radio waves, and detection equipment to produce images of sections of the brain. The people behind the invention: Raymond Damadian (1936- ), an American physicist and inventor Paul C. Lauterbur (1929- ), an American chemist Peter Mansfield (1933- ), a scientist at the University of Nottingham, England Peering into the Brain Doctors have always wanted the ability to look into the skull and see the human

brain without harming the patient who is being examined. Over the years, various attempts were made to achieve this ability. At one time, the use of X rays, which were first used byWilhelm Conrad Röntgen in 1895, seemed to be an option, but it was found that X rays are absorbed by bone, so the skull made it impossible to use X-ray technology to view the brain. The relatively recent use of computed tomography (CT) scanning, a computer-assisted imaging technology, made it possible to view sections of the head and other areas of the body, but the technique requires that the part of the body being “imaged,” or viewed, be subjected to a small amount of radiation, thereby putting the patient at risk. Positron emission tomography (PET) could also be used, but it requires that small amounts of radiation be injected into the patient, which also puts the patient at risk. Since the early 1940’s, however, a new technology had been developing. This technology, which appears to pose no risk to patients, is called “nuclear magnetic resonance spectroscopy.” It was first used to study the molecular structures of pure samples of chemicals. This method developed until it could be used to follow one chemical as it changed into another, and then another, in a living cell. By 1971, Raymond Damadian had proposed that body images that were more vivid and more useful than X rays could be produced by means of nuclear magnetic resonance spectroscopy. In 1978, he founded his own company, FONAR, which manufactured the scanners that are necessary for the technique. Magnetic Resonance Images The first nuclear magnetic resonance images (MRIs) were published by Paul Lauterbur in 1973. Although there seemed to be no possibility that MRI could be harmful to patients, everyone involved in MRI research was very cautious. In 1976, Peter Mansfield, at the University of Nottingham, England, obtained an MRI of his partner’s finger. The next year, Paul Bottomley, a member ofWaldo Hinshaw’s research group at the same university, put his left wrist into an experimental machine that the group had developed. A vivid cross section that showed layers of skin, muscle, bone, muscle, and skin, in that order, appeared on the machine’s monitor. Studies with animals showed no apparent memory or other brain problems. In 1978, Electrical and Musical Industries (EMI), a British corporate pioneer in electronics that merged with Thorn in 1980, obtained the first MRI of the human head. It took six minutes. An MRI of the brain, or any other part of the body, is made possible by the water content of the body. The gray matter of the brain contains more water than the white matter does. The blood vessels and the blood itself also have water contents that are different from those of other parts of the brain. Therefore, the different structures and areas of the brain can be seen clearly in an MRI. Bone contains very little water, so it does not appear on the monitor. This is why the skull and the backbone cause no interference when the brain or the spinal cord is viewed. Every water molecule contains two hydrogen atoms and one oxygen atom. A strong electromagnetic field causes the hydrogen molecules to line up like marchers in a parade. Radio waves can be used to change the position of these parallel hydrogen molecules. When the radio waves are discontinued, a small radio signal is produced as the molecules return to their marching position. This distinct radio signal is the basis for the production of the image on a computer screen.Hydrogen was selected for use in MRI work because it is very abundant in the human body, it is part of the water molecule, and it has the proper magnetic qualities. The nucleus of the hydrogen atom consists of a single proton, a particle with a positive charge. The signal from the hydrogen’s proton is comparatively strong. There are several methods by which the radio signal from the hydrogen atom can be converted into an image. Each method uses a computer to create first a two-dimensional, then a threedimensional, image. Peter Mansfield’s team at the University of Nottingham holds the patent for the slice-selection technique that makes it possible to excite and image selectively a specific cross section of the brain or any other part of the body. This is the key patent in MRI technology. Damadian was granted a patent that described the use of two coils, one to drive and one to pick up signals across selected portions of the human body. EMI, the company that introduced the X-ray scanner for CT images, developed a commercial prototype for the MRI. The British Technology Group, a state-owned company that helps to bring innovations to the marketplace, has sixteen separate MRIrelated patents. Ten years after EMI produced the first image of the human brain, patents and royalties were still being sorted out. Consequences MRI technology has revolutionized medical diagnosis, especially in regard to the brain and the spinal cord. For example, in multiple sclerosis, the loss of the covering on nerve cells can be detected. Tumors can be identified accurately. The painless and noninvasive use of MRI has almost completely replaced the myelogram, which involves using a needle to inject dye into the spine. Although there is every indication that the use of MRI is very safe, there are some people who cannot benefit from this valuable tool. Those whose bodies contain metal cannot be placed into the MRI machine. No one instrument can meet everyone’s needs. The development of MRI stands as an example of the interaction of achievements in various fields of science. Fundamental physics, biochemistry, physiology, electronic image reconstruction, advances in superconducting wires, the development of computers, and advancements in anatomy all contributed to the development of MRI. Its development is also the result of international efforts. Scientists and laboratories in England and the United States pioneered the technology, but contributions were also made by scientists in France, Switzerland, and Scotland. This kind of interaction and cooperation can only lead to greater understanding of the human brain.

Neutrino detector

The invention:Adevice that provided the first direct evidence that the Sun runs on thermonuclear power and challenged existing models of the Sun. The people behind the invention: Raymond Davis, Jr. (1914- ), an American chemist John Norris Bahcall (1934- ), an American astrophysicist Missing Energy In 1871, Hermann von Helmholtz, the German physicist, anatomist, and physiologist, suggested that no ordinary chemical reaction could be responsible for the enormous energy output of the Sun. By the 1920’s, astrophysicists had realized that the energy radiated by the Sun must come from nuclear fusion, in which protons or nuclei combine to form larger nuclei and release energy.

These reactions were assumed to be taking place deep in the interior of the Sun, in an immense thermonuclear furnace, where the pressures and temperatures were high enough to allow fusion to proceed. Conventional astronomical observations could record only the particles of light emitted by the much cooler outer layers of the Sun and could not provide evidence for the existence of a thermonuclear furnace in the interior. Then scientists realized that the neutrino might be used to prove that this huge furnace existed. Of all the particles released in the fusion process, only one type—the neutrino— interacts so infrequently with matter that it can pass through the Sun and reach the earth. These neutrinos provide a way to verify directly the hypothesis of thermonuclear energy generated in stars. The neutrino was “invented” in 1930 by the American physicist Wolfgang Pauli to account for the apparent missing energy in the beta decay, or emission of an electron, from radioactive nuclei. He proposed that an unseen nuclear particle, which he called a neutrino, was also emitted in beta decay, and that it carried off the “missing” energy. To balance the energy but not be observed in the decay process, Pauli’s hypothetical particle had to have no electrical charge, have little or no mass, and interact only very weakly with ordinary matter. Typical neutrinos would have to be able to pass through millions of miles of ordinary matter in order to reach the earth. Scientists’ detectors, and even the whole earth or Sun, were essentially transparent as far as Pauli’s neutrinos were concerned. Because the neutrino is so difficult to detect, it took more than twenty-five years to confirm its existence. In 1956, Clyde Cowan and Frederick Reines, both physicists at the Los Alamos National Laboratory, built the world’s largest scintillation counter, a device to detect the small flash of light given off when the neutrino strikes (“interacts” with) a certain substance in the apparatus. They placed this scintillation counter near the Savannah River Nuclear Reactor, which was producing about 1 trillion neutrinos every second. Although only one neutrino interaction was observed in their detector every twenty minutes, Cowan and Reines were able to confirm the existence of Pauli’s elusive particle. The task of detecting the solar neutrinos was even more formidable. If an apparatus similar to the Cowan and Reines detector were employed to search for the neutrinos from the Sun, only one interaction could be expected every few thousand years. Missing Neutrinos At about the same time that Cowan and Reines performed their experiment, another type of neutrino detector was under development by Raymond Davis, Jr., a chemist at the Brookhaven National Laboratory. Davis employed an idea, originally suggested in 1948 by the nuclear physicist Bruno Pontecorvo, that when a neutrino interacts with a chlorine-37 nucleus, it produces a nucleus of argon 37. Any argon so produced could then be extracted from large volumes of chlorine-rich liquid by passing helium gas through the liquid. Since argon 37 is radioactive, it is relatively easy to detect. Davis tested a version of this neutrino detector, containing about 3,785 liters of carbon tetrachloride liquid, near a nuclear reactor at the Brookhaven National Laboratory from 1954 to 1956. In the scientific paper describing his results, Davis suggested that this type of neutrino detector could be made large enough to permit detection of solar neutrinos.Although Davis’s first attempt to detect solar neutrinos from a limestone mine at Barberton, Ohio, failed, he continued his search with a much larger detector 1,478 meters underground in the Homestake Gold Mine in Lead, South Dakota. The cylindrical tank (6.1 meters in diameter, 16 meters long, and containing 378,540 liters of perchloroethylene) was surrounded by water to shield the detector from neutrons emitted by trace quantities of uranium and thorium in the walls of the mine. The experiment was conducted underground to shield it from cosmic radiation. To describe his results, Davis coined a new unit, the “solar neutrino unit” (SNU), with 1 SNU indicating the production of one atom of argon 37 every six days. Astrophysicist John Norris Bahcall, using the best available astronomical models of the nuclear reactions going on in the sun’s interior, as well as the physical properties of the neutrinos, had predicted a capture rate of 50 SNUs in 1963. The 1967 results from Davis’s detector, however, had an upper limit of only 3 SNUs.The main significance of the detection of solar neutrinos by Davis was the direct confirmation that thermonuclear fusion must be occurring at the center of the Sun. The low number of solar neutrinos Davis detected, however, has called into question some of the fundamental beliefs of astrophysics. As Bahcall explained: “We know more about the Sun than about any other star. . . . The Sun is also in what is believed to be the best-understood stage of stellar evolution. . . . If we are to have confidence in the many astronomical and cosmological applications of the theory of stellar evolution, it ought at least to give the right answers about the Sun.” Many solutions to the problem of the “missing” solar neutrinos have been proposed. Most of these solutions can be divided into two broad classes: those that challenge the model of the sun’s interior and those that challenge the understanding of the behavior of the neutrino. Since the number of neutrinos produced is very sensitive to the temperature of the sun’s interior, some astrophysicists have suggested that the true solar temperature may be lower than expected. Others suggest that the sun’s outer layer may absorb more neutrinos than expected. Some physicists, however, believe neutrinos may occur in several different forms, only one of which can be detected by the chlorine detectors.Davis’s discovery of the low number of neutrinos reaching Earth has focused years of attention on a better understanding of how the Sun generates its energy and how the neutrino behaves. New and more elaborate solar neutrino detectors have been built with the aim of understanding stars, including the Sun, as well as the physics and behavior of the elusive neutrino.

Neoprene

The invention: The first commercially practical synthetic rubber, Neoprene gave a boost to polymer chemistry and the search for new materials. The people behind the invention: Wallace Hume Carothers (1896-1937), an American chemist Arnold Miller Collins (1899- ), an American chemist Elmer Keiser Bolton (1886-1968), an American chemist Julius Arthur Nieuwland (1879-1936), a Belgian American priest, botanist, and chemist Synthetic Rubber: A Mirage? The growing dependence of the industrialized nations upon elastomers (elastic substances) and the shortcomings of natural rubber motivated the twentieth century quest for rubber substitutes. By 1914

, rubber had become nearly as indispensable as coal or iron. The rise of the automobile industry, in particular, had created a strong demand for rubber. Unfortunately, the availability of rubber was limited by periodic shortages and spiraling prices. Furthermore, the particular properties of natural rubber, such as its lack of resistance to oxygen, oils, and extreme temperatures, restrict its usefulness in certain applications. These limitations stimulated a search for special-purpose rubber substitutes. Interest in synthetic rubber dates back to the 1860 discovery by the English chemist Greville Williams that the main constituent of rubber is isoprene, a liquid hydrocarbon. Nineteenth century chemists attempted unsuccessfully to transform isoprene into rubber. The first large-scale production of a rubber substitute occurred duringWorldWar I. ABritish blockade forced Germany to begin to manufacture methyl rubber in 1916, but methyl rubber turned out to be a poor substitute for natural rubber. When the war ended in 1918, a practical synthetic rubber was still only a mirage. Nevertheless, a breakthrough was on the horizon.Mirage Becomes Reality In 1930, chemists at E. I. Du Pont de Nemours discovered the elastomer known as neoprene. Of the more than twenty chemists who helped to make this discovery possible, four stand out: Elmer Bolton, Julius Nieuwland, Wallace Carothers, and Arnold Collins. Bolton directed Du Pont’s drystuffs department in the mid- 1920’s. Largely because of the rapidly increasing price of rubber, he initiated a project to synthesize an elastomer from acetylene, a gaseous hydrocarbon. In December, 1925, Bolton attended the American Chemical Society’s convention in Rochester, New York, and heard a presentation dealing with acetylene reactions. The presenter was Julius Nieuwland, the foremost authority on the chemistry of acetylene. Nieuwland was a professor of organic chemistry at the University of Notre Dame. (One of his students was the legendary football coach Knute Rockne.) The priest-scientist had been investigating acetylene reactions for more than twenty years. Using a copper chloride catalyst he had discovered, he isolated a new compound, divinylacetylene (DVA). He later treated DVA with a vulcanizing (hardening) agent and succeeded in producing a rubberlike substance, but the substance proved to be too soft for practical use. Bolton immediately recognized the importance of Nieuwland’s discoveries and discussed with him the possibility of using DVAas a raw material for a synthetic rubber. Seven months later, an alliance was formed that permitted Du Pont researchers to use Nieuwland’s copper catalyst. Bolton hoped that the catalyst would be the key to making an elastomer from acetylene. As it turned out, Nieuwland’s catalyst was indispensable for manufacturing neoprene. Over the next several years, Du Pont scientists tried unsuccessfully to produce rubberlike materials. Using Nieuwland’s catalyst, they managed to prepare DVA and also to isolate monovinylacetylene (MVA), a new compound that eventually proved to be the vital intermediate chemical in the making of neoprene. Reactions of MVA and DVA, however, produced only hard, brittle materials. In 1928, Du Pont hired a thirty-one-year-old Harvard instructor, Wallace Carothers, to direct the organic chemicals group. He began a systematic exploration of polymers (complex molecules). In early 1930, he accepted an assignment to investigate the chemistry of DVA. He appointed one of his assistants, Arnold Collins, to conduct the laboratory experiments. Carothers suggested that Collins should explore the reaction between MVA and hydrogen chloride. His suggestion would lead to the discovery of neoprene. One of Collins’s experiments yielded a new liquid, and on April 17, 1930, he recorded in his laboratory notebook that the liquid had solidified into a rubbery substance. When he dropped it on a bench, it bounced. This was the first batch of neoprene. Carothers named Collins’s liquid “chloroprene.” Chloroprene is analogous structurally to isoprene, but it polymerizes much more rapidly. Carothers conducted extensive investigations of the chemistry of chloroprene and related compounds. His studies were the foundation for Du Pont’s development of an elastomer that was superior to all previously known synthetic rubbers. Du Pont chemists, including Carothers and Collins, formally introduced neoprene—originally called “DuPrene”—on November 3, 1931, at the meeting of the American Chemical Society in Akron, Ohio. Nine months later, the new elastomer began to be sold. Impact The introduction of neoprene was a milestone in humankind’s development of new materials. It was the first synthetic rubber worthy of the name. Neoprene possessed higher tensile strength than rubber and much better resistance to abrasion, oxygen, heat, oils, and chemicals. Its main applications included jacketing for electric wires and cables, work-shoe soles, gasoline hoses, and conveyor and powertransmission belting. By 1939, when Adolf Hitler’s troops invaded Poland, nearly every major industry in America was using neoprene. After the Japanese bombing of Pearl Harbor, in 1941, the elastomer became even more valuable to the United States. It helped the United States and its allies survive the critical shortage of natural rubber that resulted when Japan seized Malayan rubber plantations. A scientifically and technologically significant side effect of the introduction of neoprene was the stimulus that the breakthrough gave to polymer research. Chemists had long debated whether polymers were mysterious aggregates of smaller units or were genuine molecules. Carothers ended the debate by demonstrating in a series of now-classic papers that polymers were indeed ordinary— but very large—molecules. In the 1930’s, he put polymer studies on a firm footing. The advance of polymer science led, in turn, to the development of additional elastomers and synthetic fibers, including nylon, which was invented by Carothers himself in 1935.

Microwave cooking

The invention: System of high-speed cooking that uses microwave radition to agitate liquid molecules to raise temperatures by friction. The people behind the invention: Percy L. Spencer (1894-1970), an American engineer Heinrich Hertz (1857-1894), a German physicist James Clerk Maxwell (1831-1879), a Scottish physicist The Nature of Microwaves Microwaves are electromagnetic waves, as are radio waves, X rays, and visible light. Water waves

and sound waves are waveshaped disturbances of particles in the media—water in the case of water waves and air or water in the case of sound waves—through which they travel. Electromagnetic waves, however, are wavelike variations of intensity in electric and magnetic fields. Electromagnetic waves were first studied in 1864 by James Clerk Maxwell, who explained mathematically their behavior and velocity. Electromagnetic waves are described in terms of their “wavelength” and “frequency.” The wavelength is the length of one cycle, which is the distance from the highest point of one wave to the highest point of the next wave, and the frequency is the number of cycles that occur in one second. Frequency is measured in units called “hertz,” named for the German physicist Heinrich Hertz. The frequencies of microwaves run from 300 to 3,000 megahertz (1 megahertz equals 1 million hertz, or 1 million cycles per second), corresponding to wavelengths of 100 to 10 centimeters. Microwaves travel in the same way that light waves do; they are reflected by metallic objects, absorbed by some materials, and transmitted by other materials. When food is subjected to microwaves, it heats up because the microwaves make the water molecules in foods (water is the most common compound in foods) vibrate. Water is a “dipole molecule,” which means that it contains both positive and negative charges. When the food is subjected to microwaves, the dipole water molecules try to align themselves with the alternating electromagnetic field of the microwaves. This causes the water molecules to collide with one another and with other molecules in the food. Consequently, heat is produced as a result of friction. Development of the Microwave Oven Percy L. Spencer apparently discovered the principle of microwave cooking while he was experimenting with a radar device at the Raytheon Company. A candy bar in his pocket melted after being exposed to microwaves. After realizing what had happened, Spencer made the first microwave oven from a milk can and applied for two patents, “Method of Treating Foodstuffs” and “Means for Treating Foodstuffs,” on October 8, 1945, giving birth to microwaveoven technology. Spencer wrote that his invention “relates to the treatment of foodstuffs and, more particularly, to the cooking thereof through the use of electromagnetic energy.” Though the use of electromagnetic energy for heating was recognized at that time, the frequencies that were used were lower than 50 megahertz. Spencer discovered that heating at such low frequencies takes a long time. He eliminated the time disadvantage by using shorter wavelengths in the microwave region. Wavelengths of 10 centimeters or shorter were comparable to the average dimensions of foods. When these wavelengths were used, the heat that was generated became intense, the energy that was required was minimal, and the process became efficient enough to be exploited commercially. Although Spencer’s patents refer to the cooking of foods with microwave energy, neither deals directly with a microwave oven. The actual basis for a microwave oven may be patents filed by other researchers at Raytheon. Apatent by Karl Stiefel in 1949 may be the forerunner of the microwave oven, and in 1950, Fritz Gross received a patent entitled “Cooking Apparatus,” which specifically describes an oven that is very similar to modern microwave ovens. Perhaps the first mention of a commercial microwave oven was made in the November, 1946, issue of Electronics magazine. This article described the newly developed Radarange as a device that could bake biscuits in 29 seconds, cook hamburgers in 35 seconds,and grill a hot dog in 8 to 10 seconds. Another article that appeared a month later mentioned a unit that had been developed specifically for airline use. The frequency used in this oven was 3,000 megahertz. Within a year, a practical model 13 inches wide, 14 inches deep, and 15 inches high appeared, and several new models were operating in and around Boston. In June, 1947, Electronics magazine reported the installation of a Radarange in a restaurant, signaling the commercial use of microwave cooking. It was reported that this method more than tripled the speed of service. The Radarange became an important addition to a number of restaurants, and in 1948, Bernard Proctor and Samuel Goldblith used it for the first time to conduct research into microwave cooking. In the United States, the radio frequencies that can be used for heating are allocated by the Federal Communications Commission (FCC). The two most popular frequencies for microwave cooking are 915 and 2,450 megahertz, and the 2,450 frequency is used in home microwave ovens. It is interesting that patents filed by Spencer in 1947 mention a frequency on the order of 2,450 megahertz. This fact is another example of Spencer’s vision in the development of microwave cooking principles. The Raytheon Company concentrated on using 2,450 megahertz, and in 1955, the first domestic microwave oven was introduced. It was not until the late 1960’s, however, that the price of the microwave oven decreased sufficiently for the device to become popular. The first patent describing a microwave heating system being used in conjunction with a conveyor was issued to Spencer in 1952. Later, based on this development, continuous industrial applications of microwaves were developed. Impact Initially, microwaves were viewed as simply an efficient means of rapidly converting electric energy to heat. Since that time, however, they have become an integral part of many applications. Because of the pioneering efforts of Percy L. Spencer, microwave applications in the food industry for cooking and for other processing operations have flourished. In the early 1970’s, there were eleven microwave oven companies worldwide, two of which specialized in food processing operations, but the growth of the microwave oven industry has paralleled the growth in the radio and television industries. In 1984, microwave ovens accounted for more shipments than had ever been achieved by any appliance—9.1 million units. By 1989, more than 75 percent of the homes in the United States had microwave ovens, and in the 1990’s, microwavable foods were among the fastest-growing products in the food industry. Microwave energy facilitates reductions in operating costs and required energy, higher-quality and more reliable products, and positive environmental effects. To some degree, the use of industrial microwave energy remains in its infancy.Newand improved applications of microwaves will continue to appear.

Memory metal

Memory metal The invention: Known as nitinol, a metal alloy that returns to its original shape, after being deformed, when it is heated to the proper temperature. The person behind the invention: William Buehler (1923- ), an American metallurgist The Alloy with a Memory In 1960,William Buehler developed an alloy that consisted of 53 to 57 percent nickel (by weight) and the balance titanium. This alloy, which is called nitinol, turned out to have remarkable properties. Nitinol is a “memory metal,” which means that, given the proper conditions, objects made of nitinol can be restored to their original shapes even after they have been radically deformed. The return to the original shape

is triggered by heating the alloy to a moderate temperature. As the metal “snaps back” to its original shape, considerable force is exerted and mechanical work can be done. Alloys made of nickel and titanium have great potential in a wide variety of industrial and government applications. These include: for the computer market, a series of high-performance electronic connectors; for the medical market, intravenous fluid devices that feature precise fluid control; for the consumer market, eyeglass frame components; and, for the industrial market, power cable couplings that provide durability at welded joints. The Uncoiling Spring At one time, the “uncoiling spring experiment” was used to amuse audiences, and a number of scientists have had fun with nitinol in front of unsuspecting viewers. It is now generally recognized that the shape memory effect involves a thermoelastic transformation at the atomic level. This process is unique in that the transformation back to the original shape occurs as a result of stored elastic energy that assists the chemical driving force that is unleashed by heating the metal.The mechanism, simply stated, is that shape memory alloys are rather easily deformed below their “critical temperature.” Provided that the extent of the deformation is not too great, the original, undeformed state can be recovered by heating the alloy to a temperature just below the critical temperature. It is also significant that substantial stresses are generated when a deformed specimen “springs back” to its original shape. This phenomenon is very peculiar compared to the ordinary behavior of most materials. Researchers at the Naval Ordnance Laboratory discovered nitinol by accident in the process of trying to learn how to make titanium less brittle. They tried adding nickel, and when they were showing a wire of the alloy to some administrators, someone smoking a cigar held his match too close to the sample, causing the nitinol to spring back into shape. One of the first applications of the discovery was a new way to link hydraulic lines on the Navy’s F-14 fighter jets. The nitinol “sleeve” was cooled with liquid nitrogen, which enlarged the sample. Then it was slipped into place between two pipes. When the sleeve was warmed up, it contracted, clamping the pipes together and keeping them clamped with a force of nearly 50,000 pounds per square inch. Nitinol is not an easy alloy with which to work. When it is drilled or passed through a lathe, it becomes hardened and resists change. Welding nitinol and electroplating it have become manufacturing nightmares. It also resists taking on a desired shape. The frictional forces of many processes heat the nitinol, which activates its memory. Its fantastic elasticity also causes difficulties. If it is placed in a press with too little force, the spring comes out of the die unchanged.With too much force, the metal breaks into fragments. Using oil as a cooling lubricant and taking a step-wise approach to altering the alloy, however, allows it to be fashioned into particular shapes. One unique use of nitinol occurs in cardiac surgery. Surgical tools made of nitinol can be bent up to 90 degrees, allowing them to be passed into narrow vessels and then retrieved. The tools are then straightened out in an autoclave so that they can be reused.Many of the technical problems of working with nitinol have been solved, and manufacturers of the alloy are selling more than twenty different nitinol products to countless companies in the fields of medicine, transportation, consumer products, and toys. Nitinol toys include blinking movie posters, butterflies with flapping wings, and dinosaurs whose tails move; all these applications are driven by a contracting bit of wire that is connected to a watch battery. The “Thermobile” and the “Icemobile” are toys whose wheels are set in motion by hot water or by ice cubes. Orthodontists sometimes use nitinol wires and springs in braces because the alloy pulls with a force that is more gentle and even than that of stainless steel, thus causing less pain. Nitinol does not react with organic materials, and it is also useful as a new type of blood-clot filter. Best of all, however, is the use of nitinol for eyeglass frames. If the wearer deforms the frames by sitting on them (and people do so frequently), the optometrist simply dips the crumpled frames in hot water and the frames regain their original shape. From its beginnings as an “accidental” discovery, nitinol has gone on to affect various fields of science and technology, from the “Cryofit” couplings used in the hydraulic tubing of aircraft to the pin-and-socket contacts used in electrical circuits. Nitinol has also found its way into integrated circuit packages. In an age of energy conservation, the unique phase transformation of nickel-titanium alloys allows them to be used in lowtemperature heat engines. The world has abundant resources of low-grade thermal energy, and the recovery of this energy can be accomplished by the use of materials such as nitinol. Despite the limitations imposed on heat engines working at low temperatures across a small temperature change, sources of low-grade heat are so widespread that the economical conversion of a fractional percentage of that energy could have a significant impact on the world’s energy supply. Nitinol has also become useful as a material capable of absorbing internal vibrations in structural materials, and it has been used as “Harrington rods” to treat scoliosis (curvature of the spine).