For chemistry class, I just finished my report on Ernest Lawrence and the cyclotron, only took 2 days. Here it is if you're bored and have nothing better to do.
Ernest Lawrence’s Cyclotron:
N U C L E A R C O L L I S I O N
Ernest Lawrence was born on August 8th, 1901 in Canton, South Dakota. His parents, Gustavus and Gunda Lawrence, were immigrants from Norway. Ernest attended Canton High School, and from 1919 to 1922, proceeded to the University of South Dakota to receive a Bachelor of Arts in Chemistry and a Master of Arts from the University of Minnesota. In 1925, he obtained a Ph.D. in Chemistry at Yale University. For the next three years, he did physics research at Yale University, two years at the National Research Fellow, and one as Associate Professor of Physics. In 1928, he was appointed Associate Professor of Physics at the University of California, Berkley at age 29. In 1936, he also became the Director of the University’s Radiation Laboratory. He stayed in these positions for the remainder of his life.
Ernest Lawrence’s early work was on ionization phenomena and the measurement of ionization potentials of metal vapors. In 1929, he invented the cyclotron, a device that accelerates particles and smashes them on a targeted. His first cyclotron measured only 5 inches in diameter and boosted hydrogen ions to energies of 80,000 eV (electron volts). A cyclotron works by using two D-shaped magnets, called dees, separated by a gap, which accelerated the particles each time around. Each time the particles would pass through the gap, the charges of the dees would switch. The particles would spin around the dees in a circular motion due to the circular magnetic field, and because the gap had an oscillating voltage, the ions would accelerate. When they accelerate, they move further away from the center, spiraling eventually to the edge. At the edge would be a calculatedly positioned straight tube jetting off of the circular dees; the speeding ions speed down the tube colliding onto a target (go to this website to see a good animation of this procedure- http://www.aip.org/history/lawrence/ima ... mation.gif). The target measures the energy of the ions in eV. One electron volt is equal to the amount of energy that one electron gains when accelerating through a potential difference of one volt. A volt equals joules/coulombs (V = J / C). A coulomb is the ampere (unit of charge of a particle) for each second, so C = A · S. The potential difference, or electromotive force, is the difference of potential energy between two points on a conductor carrying one ampere when the power degenerated between the two points equals one watt (1 watt equals joules/seconds, W = J / s). From all this, one gets 1 eV = 1.602x10-19 joules, which is purely a measure of energy for one electron.
Lawrence found out that his cyclotron could exploit the laws of electrodynamics. The centripetal acceleration of an ion in the cyclotron’s perpendicular magnetic field B equals the charge of the ion (e) times its velocity (v) times the magnetic field (B) divided by the velocity of light (c), so the centripetal acceleration = evB/c. The mechanical centrifugal force equal the mass (m) times its velocity squared (v) divided by the radius from the center (r), so F = mv2/r. Balancing the force and acceleration for a stable orbit is called the cyclotron equation, v/r = eB/mc. Lawrence also discovered that the frequency (f) at which particles rotated around the dees is independent from the radius from which the ions are from the center (f = v/2pr = eB/2pmc \ r = mc), which means that as the particles moves away from the center, its velocity increases, keeping the frequency is constant. Because the frequency is uniform, the oscillating magnetic dees can switch charges at a uniform pace, and the ions will always pass through the gap at the same times at the same frequency regardless of the radius. This also meant that the ions could be accelerated greatest without much force. The frequency in Lawrence’s cyclotron was about 4 million cycles per second.
With all this knowledge, Lawrence was ready for experiments with the cyclotron. His very first was a 4.5-inch diameter homemade cyclotron made from glass, sealing wax, and bronze, capable of an estimated 80,000 eV. His real first cyclotron was his 11-inch diameter machine, which would break the 1 MeV (million electron volts) barrier. It used an 80-ton magnet and used deuterons (a deuteron is the nucleus of deuterium [D], which is an isotope of hydrogen, composed of one proton and one neutron). It achieved 1.1 MeV. This means that the energy of one accelerated deuteron equals 1.1 MeV, as compared to the usual 1 eV for one accelerated electron. Lawrence had high hopes though, and he would have to use more laboratory space at Berkley University to expand his experiments. With only 1.1 MeV, nothing new had been created yet. The 11-inch cyclotron was housed in the Le Conte Hall, but Lawrence’s next cyclotron, a 27-inch, would not fit. With much persuasion, the university signed over the Civil Engineering Testing Laboratory in 1931, which was scarcely used, to Ernest Lawrence, renaming it the Radiation Laboratory. The 27-inch cyclotron was quick changed to a 37-inch diameter, which could accelerate deuterons to 8 MeV, and alpha particles (a, the nucleus of a helium atom, two protons and two neutrons) to 16 MeV. By 1936, these experiments were used to create radioisotopes and the first synthetic element ever made, technetium. Technetium is atomic number 43, with an amu of [98]. Studies have undergone for discovering technetium in nature, but with no success, except that it can exist in certain types of stars. Technetium is created by bombarding molybdenum with deuterons. Mo42 + D2 = Tc43. On July 1st, 1936, Berkley officially made the Radiation Laboratory dedicated to the pursuit of “nuclear science”, instead of just accelerator physics.
In 1932, Lawrence married Molly Blumer, whom he had met at Yale University, and was the eldest daughter of a professor of medicine at Yale. They had two sons and four daughters. Many scientists like Lawrence never marry because they are too consumed with research and work.
In 1936, Ernest Lawrence’s brother, John Lawrence, who was a physician, joined forces with Ernest to explore the medical possibilities of the cyclotron. For this, a new 60-inch diameter was to be built. Because of the vast number of physicists, chemists, engineers, and even biologists being interested in the cyclotron, a new building was constructed next to the Radiation Laboratory, called the Crocker Laboratory, which housed the 60-inch cyclotron. Construction of the building and particle accelerator was completed in 1939, and was described by visitors as a “truly colossal machine.” Its magnet weighed 220 tons. John Lawrence did many medical tests with the cyclotron, even though the main purpose of it was to gain financial support to pay for the cyclotron, a hefty $550,000 bill in 1939. The 37-inch cyclotron was used for the discoveries of carbon-14, neptunium, and plutonium in 1940. In 1941 the cyclotron was used in the discovery of mesons (cosmic particles, such as pions and kaons made from quarks), and antiparticles, including the positron.
In 1939, Ernest Lawrence was award the Nobel Prize for Physics, for his invention of the cyclotron, with regards to the creation of artificial radioisotopes. The award helped to convince the Rockefeller Foundation to donate $1.4 million dollars to support Lawrence’s last major cyclotron endeavor, a 184-inch cyclotron, capable of launching particles at over 100 MeV. It took a new entire building to house it; the machine was 160 feet in diameter, 100 feet tall, and the magnetic dees weighed 4,000 tons. Construction of the massive 184-inch cyclotron (which was actually a synchrocyclotron) was completed in 1946. The new giant cyclotron didn’t do much more than the 60-inch though.
As World War II started, the U.S. government recruited Ernest Lawrence into the Manhattan Project. Only a few years before the war, German scientists discovered that when uranium-235 was bombarded with neutrons, they split into two pieces, a process called fission, and shared the findings with American scientists. Lawrence tried this in with his 60-inch cyclotron and was amazed at what he had missed in the past. Lawrence was a front man in the construction of the atomic bomb. After the uranium bomb was detonated over Hiroshima, Lawrence played a part in obtaining an international agreement for the suspension of atomic bomb testing; he was a member of the U.S. delegation to the 1958 Geneva Convention.
Ernest Lawrence died on August 27th, 1958 from chronic colitis at the age of 57. In his honor, Berkley University renamed the Radiation Laboratory, the Lawrence Radiation Laboratory. In 1995, they renamed it yet again, to the Ernest Orlando Lawrence Berkley National Laboratory, to fully honor one of the world’s greatest scientists.
Ernest Lawrence’s cyclotron inspired many scientists up to today, like Enrico Fermi (1901-1954) and his linear particle accelerator. In 1994, CERN (Europäisches Laboratorium für Teilchenphysik, European Laboratory for Particle Physics) in Geneva, Switzerland, initiated the construction of a 14 TeV (trillion electron volts) particle accelerator, called the Large Hadron Collider (LHC). A hadron is any particle made of quarks and is subject to strong nuclear force. The LHC is basically a very large linear accelerator that uses accelerating protons down a tube. The protons spiral down the tube by enormous magnets, to collide with another beam of protons. The particles will be reaching speeds close to the speed of light (3x106 m/s). The accelerator can also use electrons and positrons. With the power of 14 TeV, new particles will be created, and is said to allow a complete understanding of the origin of mass. Testing is so far scheduled to begin in 2004 for a 10 TeV, and the 14 TeV accelerator should be operating by 2008. There is also a design at the Fermi National Accelerator Laboratory about a VLHC (Very Large Hadron Collider) that can attain energies of 20 TeV. 20 TeV may seem like a large number, but it’s really only 3.204x10-6 J, a rather small number, but one must remember, this is for only one particle.
Without scientist Ernest Lawrence, the world would not today have the technology and knowledge of synthetic elements, radioisotopes, antiparticles, and quarks. Because the cyclotron has been one of the most important inventions for science, Ernest Lawrence was awarded the 1939 Nobel Prize for Physics, and in 1961, element 103 was named after him, lawrencium. Ernest Lawrence is the father of modern particle acceleration science; from his work, mankind may soon discover the origin of mass.
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