06 June 2009

Cyclotron

The invention: The first successful magnetic resonance accelerator for protons, the cyclotron gave rise to the modern era of particle accelerators, which are used by physicists to study the structure of atoms. The people behind the invention: Ernest Orlando Lawrence (1901-1958), an American nuclear physicist who was awarded the 1939 Nobel Prize in Physics M. Stanley Livingston (1905-1986), an American nuclear physicist Niels Edlefsen (1893-1971), an American physicist David Sloan (1905- ), an American physicist and electrical engineer The Beginning of an Era The invention of the cyclotron by Ernest Orlando Lawrence marks the beginning of the modern era of high-energy physics. Although the energies of newer accelerators have increased steadily, the principles incorporated in the cyclotron have been fundamental to succeeding generations of accelerators, many of which were also developed in Lawrence’s laboratory. The care and support for such machines have also given rise to “big science”: the massing of scientists, money, and machines in support of experiments to discover the nature of the atom and its constituents. At the University of California, Lawrence took an interest in the new physics of the atomic nucleus, which had been developed by the British physicist Ernest Rutherford and his followers in England, and which was attracting more attention as the development of quantum mechanics seemed to offer solutions to problems that had long preoccupied physicists. In order to explore the nucleus of the atom, however, suitable probes were required. An artificial means of accelerating ions to high energies was also needed. During the late 1920’s, various means of accelerating alpha particles, protons (hydrogen ions), and electrons had been tried, but none had been successful in causing a nuclear transformation when Lawrence entered the field. The high voltages required exceeded the resources available to physicists. It was believed that more than a million volts would be required to accelerate an ion to sufficient energies to penetrate even the lightest atomic nuclei. At such voltages, insulators broke down, releasing sparks across great distances. European researchers even attempted to harness lightning to accomplish the task, with fatal results. Early in April, 1929, Lawrence discovered an article by a German electrical engineer that described a linear accelerator of ions that worked by passing an ion through two sets of electrodes, each of which carried the same voltage and increased the energy of the ions correspondingly. By spacing the electrodes appropriately and using an alternating electrical field, this “resonance acceleration” of ions could speed subatomic particles to many times the energy applied in each step, overcoming the problems presented when one tried to apply a single charge to an ion all at once. Unfortunately, the spacing of the electrodes would have to be increased as the ions were accelerated, since they would travel farther between each alternation of the phase of the accelerating charge, making an accelerator impractically long in those days of small-scale physics. Fast-Moving Streams of Ions Lawrence knew that a magnetic field would cause the ions to be deflected and form a curved path. If the electrodes were placed across the diameter of the circle formed by the ions’ path, they should spiral out as they were accelerated, staying in phase with the accelerating charge until they reached the periphery of the magnetic field. This, it seemed to him, afforded a means of producing indefinitely high voltages without using high voltages by recycling the accelerated ions through the same electrodes. Many scientists doubted that such a method would be effective. No mechanism was known that would keep the circulating ions in sufficiently tight orbits to avoid collisions with the walls of the accelerating chamber. Others tried unsuccessfully to use resonance acceleration. Agraduate student, M. Stanley Livingston, continued Lawrence’s work. For his dissertation project, he used a brass cylinder 10 centimeters in diameter sealed with wax to hold a vacuum, a half-pillbox of copper mounted on an insulated stem to serve as the electrode, and a Hartley radio frequency oscillator producing 10 watts. The hydrogen molecular ions were produced by a thermionic cathode (mounted near the center of the apparatus) from hydrogen gas admitted through an aperture in the side of the cylinder after a vacuum had been produced by a pump. Once formed, the oscillating electrical field drew out the ions and accelerated them as they passed through the cylinder. The accelerated ions spiraled out in a magnetic field produced by a 10-centimeter electromagnet to a collector. By November, 1930, Livingston had observed peaks in the collector current as he tuned the magnetic field through the value calculated to produce acceleration. Borrowing a stronger magnet and tuning his radio frequency oscillator appropriately, Livingston produced 80,000-electronvolt ions at his collector on January 2, 1931, thus demonstrating the principle of magnetic resonance acceleration.Impact Demonstration of the principle led to the construction of a succession of large cyclotrons, beginning with a 25-centimeter cyclotron developed in the spring and summer of 1931 that produced one-million-electronvolt protons. With the support of the Research Corporation, Lawrence secured a large electromagnet that had been developed for radio transmission and an unused laboratory to house it: the Radiation Laboratory. The 69-centimeter cyclotron built with the magnet was used to explore nuclear physics. It accelerated deuterons, ions of heavy water or deuterium that contain, in addition to the proton, the neutron, which was discovered by Sir James Chadwick in 1932. The accelerated deuteron, which injected neutrons into target atoms, was used to produce a wide variety of artificial radioisotopes. Many of these, such as technetium and carbon 14, were discovered with the cyclotron and were later used in medicine. By 1939, Lawrence had built a 152-centimeter cyclotron for medical applications, including therapy with neutron beams. In that year, he won the Nobel Prize in Physics for the invention of the cyclotron and the production of radioisotopes. During World War II, Lawrence and the members of his Radiation Laboratory developed electromagnetic separation of uranium ions to produce the uranium 235 required for the atomic bomb. After the war, the 467-centimeter cyclotron was completed as a synchrocyclotron, which modulated the frequency of the accelerating fields to compensate for the increasing mass of ions as they approached the speed of light. The principle of synchronous acceleration, invented by Lawrence’s associate, the American physicist Edwin Mattison McMillan, became fundamental to proton and electron synchrotrons. The cyclotron and the Radiation Laboratory were the center of accelerator physics throughout the 1930’s and well into the postwar era. The invention of the cyclotron not only provided a new tool for probing the nucleus but also gave rise to new forms of organizing scientific work and to applications in nuclear medicine and nuclear chemistry. Cyclotrons were built in many laboratories in the United States, Europe, and Japan, and they became a standard tool of nuclear physics.

02 June 2009

Cyclamate

The invention: An artificial sweetener introduced to the American market in 1950 under the tradename Sucaryl. The person behind the invention: Michael Sveda (1912-1999), an American chemist A Foolhardy Experiment The first synthetic sugar substitute, saccharin, was developed in 1879. It became commercially available in 1907 but was banned for safety reasons in 1912. Sugar shortages during World War I (1914- 1918) resulted in its reintroduction. Two other artificial sweeteners, Dulcin and P-4000, were introduced later but were banned in 1950 for causing cancer in laboratory animals. In 1937, Michael Sveda was a young chemist working on his Ph.D. at the University of Illinois. Aflood in the Ohio valley had ruined the local pipe-tobacco crop, and Sveda, a smoker, had been forced to purchase cigarettes. One day while in the laboratory, Sveda happened to brush some loose tobacco from his lips and noticed that his fingers tasted sweet. Having a curious, if rather foolhardy, nature, Sveda tasted the chemicals on his bench to find which one was responsible for the taste. The culprit was the forerunner of cyclohexylsulfamate, the material that came to be known as “cyclamate.” Later, on reviewing his career, Sveda explained the serendipitous discovery with the comment: “God looks after . . . fools, children, and chemists.” Sveda joined E. I. Du Pont de Nemours and Company in 1939 and assigned the patent for cyclamate to his employer. In June of 1950, after a decade of testing on animals and humans, Abbott Laboratories announced that it was launching Sveda’s artificial sweetener under the trade name Sucaryl. Du Pont followed with its sweetener product, Cyclan. A Time magazine article in 1950 announced the new product and noted that Abbott had warned that because the product was a sodium salt, individuals with kidney problems should consult their doctors before adding it to their food.Cyclamate had no calories, but it was thirty to forty times sweeter than sugar. Unlike saccharin, cyclamate left no unpleasant aftertaste. The additive was also found to improve the flavor of some foods, such as meat, and was used extensively to preserve various foods. By 1969, about 250 food products contained cyclamates, including cakes, puddings, canned fruit, ice cream, salad dressings, and its most important use, carbonated beverages. It was originally thought that cyclamates were harmless to the human body. In 1959, the chemical was added to the GRAS (generally recognized as safe) list. Materials on this list, such as sugar, salt, pepper, and vinegar, did not have to be rigorously tested before being added to food. In 1964, however, a report cited evidence that cyclamates and saccharin, taken together, were a health hazard. Its publication alarmed the scientific community. Numerous investigations followed. Shooting Themselves in the Foot Initially, the claims against cyclamate had been that it caused diarrhea or prevented drugs from doing their work in the body. By 1969, these claims had begun to include the threat of cancer. Ironically, the evidence that sealed the fate of the artificial sweetener was provided by Abbott itself. Aprivate Long Island company had been hired by Abbott to conduct an extensive toxicity study to determine the effects of longterm exposure to the cyclamate-saccharin mixtures often found in commercial products. The team of scientists fed rats daily doses of the mixture to study the effect on reproduction, unborn fetuses, and fertility. In each case, the rats were declared to be normal. When the rats were killed at the end of the study, however, those that had been exposed to the higher doses showed evidence of bladder tumors. Abbott shared the report with investigators from the National Cancer Institute and then with the U.S. Food and Drug Administration (FDA). The doses required to produce the tumors were equivalent to an individual drinking 350 bottles of diet cola a day. That was more than one hundred times greater than that consumed even by those people who consumed a high amount of cyclamate. A six-person panel of scientists met to review the data and urged the ban of all cyclamates from foodstuffs. In October, 1969, amid enormous media coverage, the federal government announced that cyclamates were to be withdrawn from the market by the beginning of 1970. In the years following the ban, the controversy continued. Doubt was cast on the results of the independent study linking sweetener use to tumors in rats, because the study was designed not to evaluate cancer risks but to explain the effects of cyclamate use over many years. Bladder parasites, known as “nematodes,” found in the rats may have affected the outcome of the tests. In addition, an impurity found in some of the saccharin used in the study may have led to the problems observed. Extensive investigations such as the three-year project conducted at the National Cancer Research Center in Heidelberg, Germany, found no basis for the widespread ban. In 1972, however, rats fed high doses of saccharin alone were found to have developed bladder tumors. At that time, the sweetener was removed from the GRAS list. An outright ban was averted by the mandatory use of labels alerting consumers that certain products contained saccharin. Impact The introduction of cyclamate heralded the start of a new industry. For individuals who had to restrict their sugar intake for health reasons, or for those who wished to lose weight, there was now an alternative to giving up sweet food. The Pepsi-Cola company put a new diet drink formulation on the market almost as soon as the ban was instituted. In fact, it ran advertisements the day after the ban was announced showing the Diet Pepsi product boldly proclaiming “Sugar added—No Cyclamates.” Sveda, the discoverer of cyclamates, was not impressed with the FDA’s decision on the sweetener and its handling of subsequent investigations. He accused the FDAof “a massive cover-up of elemental blunders” and claimed that the original ban was based on sugar politics and bad science. For the manufacturers of cyclamate, meanwhile, the problem lay with the wording of the Delaney amendment, the legislation that regulates new food additives. The amendment states that the manufacturer must prove that its product is safe, rather than the FDAhaving to prove that it is unsafe. The onus was on Abbott Laboratories to deflect concerns about the safety of the product, and it remained unable to do so.

Cruise missile

The invention: Aircraft weapons system that makes it possible to attack both land and sea targets with extreme accuracy without endangering the lives of the pilots. The person behind the invention: Rear Admiral Walter M. Locke (1930- ), U.S. Navy project manager From the Buzz Bombs of World War II During World War II, Germany developed and used two different types of missiles: ballistic missiles and cruise missiles.Aballistic missile is one that does not use aerodynamic lift in order to fly. It is fired into the air by powerful jet engines and reaches a high altitude; when its engines are out of fuel, it descends on its flight path toward its target. The German V-2 was the first ballistic missile. The United States and other countries subsequently developed a variety of highly sophisticated and accurate ballistic missiles. The other missile used by Germany was a cruise missile called the V-1, which was also called the flying bomb or the buzz bomb. The V-1 used aerodynamic lift in order to fly, just as airplanes do. It flew relatively low and was slow; by the end of the war, the British, against whom it was used, had developed techniques for countering it, primarily by shooting it down. After World War II, both the United States and the Soviet Union carried on the Germans’ development of both ballistic and cruise missiles. The United States discontinued serious work on cruise missile technology during the 1950’s: The development of ballistic missiles of great destructive capability had been very successful. Ballistic missiles armed with nuclear warheads had become the basis for the U.S. strategy of attempting to deter enemy attacks with the threat of a massive missile counterattack. In addition, aircraft carriers provided an air-attack capability similar to that of cruise missiles. Finally, cruise missiles were believed to be too vulnerable to being shot down by enemy aircraft or surface-to-air missiles.While ballistic missiles are excellent for attacking large, fixed targets, they are not suitable for attacking moving targets. They can be very accurately aimed, but since they are not very maneuverable during their final descent, they are limited in their ability to change course to hit a moving target, such as a ship. During the 1967 war, the Egyptians used a Soviet-built cruise missile to sink the Israeli ship Elath. The U.S. military, primarily the Navy and the Air Force, took note of the Egyptian success and within a few years initiated cruise missile development programs. The Development of Cruise Missiles The United States probably could have developed cruise missiles similar to 1990’s models as early as the 1960’s, but it would have required a huge effort. The goal was to develop missiles that could be launched from ships and planes using existing launching equipment, could fly long distances at low altitudes at fairly high speeds, and could reach their targets with a very high degree of accuracy. If the missiles flew too slowly, they would be fairly easy to shoot down, like the German V-1’s. If they flew at too high an altitude, they would be vulnerable to the same type of surface-based missiles that shot down Gary Powers, the pilot of the U.S. U2 spyplane, in 1960. If they were inaccurate, they would be of little use. The early Soviet cruise missiles were designed to meet their performance goals without too much concern about how they would be launched. They were fairly large, and the ships that launched them required major modifications. The U.S. goal of being able to launch using existing equipment, without making major modifications to the ships and planes that would launch them, played a major part in their torpedo-like shape: Sea-Launched Cruise Missiles (SLCMs) had to fit in the submarine’s torpedo tubes, and Air- Launched Cruise Missiles (ALCMs) were constrained to fit in rotary launchers. The size limitation also meant that small, efficient jet engines would be required that could fly the long distances required without needing too great a fuel load. Small, smart computers were needed to provide the required accuracy. The engine and computer technologies began to be available in the 1970’s, and they blossomed in the 1980’s.The U.S. Navy initiated cruise missile development efforts in 1972; the Air Force followed in 1973. In 1977, the Joint Cruise Missile Project was established, with the Navy taking the lead. Rear Admiral Walter M. Locke was named project manager. The goal was to develop air-, sea-, and ground-launched cruise missiles. By coordinating activities, encouraging competition, and requiring the use of common components wherever possible, the cruise missile development program became a model for future weapon-system development efforts. The primary contractors included Boeing Aerospace Company, General Dynamics, and McDonnell Douglas. In 1978, SLCMs were first launched from submarines. Over the next few years, increasingly demanding tests were passed by several versions of cruise missiles. By the mid-1980’s, both antiship and antiland missiles were available. An antiland version could be guided to its target with extreme accuracy by comparing a map programmed into its computer to the picture taken by an on-board video camera. The typical cruise missile is between 18 and 21 feet long, about 21 inches in diameter, and has a wingspan of between 8 and 12 feet. Cruise missiles travel slightly below the speed of sound and have a range of around 1,350 miles (antiland) or 250 miles (antiship). Both conventionally armed and nuclear versions have been fielded. Consequences Cruise missiles have become an important part of the U.S. arsenal. They provide a means of attacking targets on land and water without having to put an aircraft pilot’s life in danger. Their value was demonstrated in 1991 during the Persian GulfWar. One of their uses was to “soften up” defenses prior to sending in aircraft, thus reducing the risk to pilots. Overall estimates are that about 85 percent of cruise missiles used in the Persian Gulf War arrived on target, which is an outstanding record. It is believed that their extreme accuracy also helped to minimize noncombatant casualties.

31 May 2009

Coronary artery bypass surgery

The invention: The most widely used procedure of its type, coronary bypass surgery uses veins from legs to improve circulation to the heart. The people behind the invention: Rene Favaloro (1923-2000), a heart surgeon Donald B. Effler (1915- ), a member of the surgical team that performed the first coronary artery bypass operation F. Mason Sones (1918- ), a physician who developed an improved technique of X-raying the heart’s arteries Fighting Heart Disease In the mid-1960’s, the leading cause of death in the United States was coronary artery disease, claiming nearly 250 deaths per 100,000 people. Because this number was so alarming, much research was being conducted on the heart. Most of the public’s attention was focused on heart transplants performed separately by the famous surgeons Christiaan Barnard and Michael DeBakey. Yet other, less dramatic procedures were being developed and studied. Amajor problem with coronary artery disease, besides the threat of death, is chest pain, or angina. Individuals whose arteries are clogged with fat and cholesterol are frequently unable to deliver enough oxygen to their heart muscles. This may result in angina, which causes enough pain to limit their physical activities. Some of the heart research in the mid-1960’s was an attempt to find a surgical procedure that would eliminate angina in heart patients. The various surgical procedures had varying success rates. In the late 1950’s and early 1960’s, a team of physicians in Cleveland was studying surgical procedures that would eliminate angina. The team was composed of Rene Favaloro, Donald B. Effler, F. Mason Sones, and Laurence Groves. They were working on the concept, proposed by Dr. Arthur M. Vineberg from McGill University in Montreal, of implanting a healthy artery from the chest into the heart. This bypass procedure would provide the heart with another source of blood, resulting in enough oxygen to overcome the angina. Yet Vineberg’s surgery was often ineffective because it was hard to determine exactly where to implant the new artery. New Techniques In order to make Vineberg’s proposed operation successful, better diagnostic tools were needed. This was accomplished by the work of Sones. He developed a diagnostic procedure, called “arteriography,” whereby a catheter was inserted into an artery in the arm, which he ran all the way into the heart. He then injected a dye into the coronary arteries and photographed them with a high-speed motionpicture camera. This provided an image of the heart, which made it easy to determine where the blockages were in the coronary arteries. Using this tool, the team tried several new techniques. First, the surgeons tried to ream out the deposits found in the narrow portion of the artery. They found, however, that this actually reduced blood flow. Second, they tried slitting the length of the blocked area of the artery and suturing a strip of tissue that would increase the diameter of the opening. This was also ineffective because it often resulted in turbulent blood flow. Finally, the team attempted to reroute the flow of blood around the blockage by suturing in other tissue, such as a portion of a vein from the upper leg. This bypass procedure removed that part of the artery that was clogged and replaced it with a clear vessel, thereby restoring blood flow through the artery. This new method was introduced by Favaloro in 1967. In order for Favaloro and other heart surgeons to perform coronary artery surgery successfully, several other medical techniques had to be developed. These included extracorporeal circulation and microsurgical techniques.Extracorporeal circulation is the process of diverting the patient’s blood flow from the heart and into a heart-lung machine. This procedure was developed in 1953 by U.S. surgeon John H. Gibbon, Jr. Since the blood does not flow through the heart, the heart can be temporarily stopped so that the surgeons can isolate the artery and perform the surgery on motionless tissue. Microsurgery is necessary because some of the coronary arteries are less than 1.5 millimeters in diameter. Since these arteries had to be sutured, optical magnification and very delicate and sophisticated surgical tools were required. After performing this surgery on numerous patients, follow-up studieswere able to determine the surgery’s effectiveness. Only then was the value of coronary artery bypass surgery recognized as an effective procedure for reducing angina in heart patients. Consequences According to the American Heart Association, approximately 332,000 bypass surgeries were performed in the United States in 1987, an increase of 48,000 from 1986. These figures show that the work by Favaloro and others has had a major impact on the health of United States citizens. The future outlook is also positive. It has been estimated that five million people had coronary artery disease in 1987. Of this group, an estimated 1.5 million had heart attacks and 500,000 died. Of those living, many experienced angina. Research has developed new surgical procedures and new drugs to help fight coronary artery disease. Yet coronary artery bypass surgery is still a major form of treatment.