Place: United States of America
Subject: biography, physics
US physicist who was responsible for the concept and development of the cyclotron. For this achievement he was awarded the 1939 Nobel Prize for Physics. As director of the Radiation Laboratories at Berkeley, California, he and his co-workers then produced a remarkable sequence of discoveries, which included the creation of radioactive isotopes and the synthesis of new transuranic elements.
Lawrence was born in Canton, South Dakota, on 8 August 1901. He went to the University of South Dakota, where he was awarded a BS degree in 1922, and then continued his studies at the University of Minnesota, specializing in physics and gaining an MA the following year. After a further two years spent at the University of Chicago, he went to Yale University where he carried out research on photoelectricity and gained his PhD in 1925. He continued at Yale as a research fellow and later as assistant professor of physics until 1928. During this period he made a precise determination of the ionization potential (the energy required to remove an electron) of the mercury atom, developed methods for spark discharges of minute duration (3 × 10−9 sec), and discovered a new method of measuring the charge-to-mass ratio of the electron (e/m). Lawrence then returned to the University of California as associate professor of physics and in 1930 he became, at 29, the youngest full professor (of physics) at Berkeley. Lawrence retained this position until the end of his life, together with the directorship of the Radiation Laboratories, which he commenced in 1936.
During World War II, Lawrence was involved with the separation of uranium-235 and plutonium for the development of the atomic bomb, and he organized the Los Alamos Scientific Laboratories at which much of the work on this project was carried out. After the war, he continued as a believer in nuclear weapons and advocated the acceleration of their development. He died in Palo Alto, California, on 27 August 1958.
In 1929 Lawrence was pondering methods of attacking the atomic nucleus with particles at high energies. The methods then developed involved the generation of very high voltages of electricity. To Lawrence, these seemed to be very limited in the long run as the electrical engineering necessary seemed likely to be technically very difficult, and their cost would eventually prove to be prohibitive. Early that same year, he came across an article in a German periodical that described a linear device for the acceleration of ions, and Lawrence realized the potential of the design for producing high-energy particles that could be directed at atomic nuclei. On carrying out the calculation to produce a machine that would produce protons with the energy of one million electronvolts, he discovered that the device would be too long for the laboratory space he had available. He therefore considered bending the accelerator so that the particles would travel in a spiral. This idea led to the cyclotron, which had two electrodes that were hollow and semicircular in shape mounted in a vacuum between the poles of a magnet. In between the two electrodes was the source of the particles. To the electrodes was connected a source of electricity whose polarity could be oscillated, positive and negative, from one electrode to the other at very high frequency. The negative field caused the particles to turn in a circular path in each electrode and each time they crossed between the electrodes they received an impetus that accelerated them further, giving them more and more energy without involving very high voltages. As this happened, the increased velocity carried the particles farther from the centre of the apparatus, producing a spiral path.
The first cyclotrons were made in 1930 and were only a few centimetres in diameter and of very crude design. They were made by Nels Edlefsen, one of Lawrence's research students, and one of them showed some indication of working. Later the same year M Stanley Livingston, another of Lawrence's research students, constructed a further small but improved device that accelerated protons to 80,000 electronvolts with 1,000 volts used on the electrodes. Once the principle had been seen to work well, larger and improved devices were made. Each new design produced particles of higher energy than its predecessor and new results were obtained from the use of the accelerated particles in nuclear transformations. One of these was the disintegration of the lithium nucleus to produce helium nuclei, confirming the first artificial transformation made by John Cockcroft and Ernest Walton in 1932, and a 68-cm/27-in model was used to produce artificial radioactivity. With increasing size, the engineering problems associated with power supplies and the production of large magnetic fields increased, and in 1936 the Radiation Laboratory with the necessary engineering and administrative facilities was opened to house the new equipment.
From his laboratory, a multitude of discoveries in chemistry, physics, and biology were made under Lawrence's direction. Hundreds of radioactive isotopes were produced, including carbon-14, iodine-131, and uranium-233. Furthermore, over the years, most of the transuranium elements were synthesized. Mesons, which were then little-known particles, were produced and studied within a laboratory for the first time at the Radiation Laboratory, and anti-particles were also found. Many of these discoveries owe their origin to other famous scientists who worked within the laboratory, but Lawrence worked tirelessly advising researchers and in making the experiments possible. Fairly early in the development of the cyclotron it became apparent that as particles were accelerated to high speeds their masses increased, as predicted by the special theory of relativity. This increase in mass caused them to lose synchronization with the oscillating electric field. The solution of this problem by Vladimir Veksler (1907-1966) and Edwin McMillan (1907-1991) independently led to the development of the synchrotron and particles of even higher energies.
Lawrence made an important contribution to physics with the invention of cyclotron, for the subsequent development of high-energy physics and the elucidation of the subatomic structure of matter was highly dependent on this machine and its successors. These have also provided radioisotopes of great value in medicine. Appropriately, Lawrence's name is remembered in the naming of element 103 as lawrencium, for it was discovered in his laboratory at Berkeley.
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