Ernest Lawrence




AMERICAN PHYSICIST
1901–1958

Ernest Orlando Lawrence was a pioneer of "big science," the use of complicated and expensive instrumentation by large teams of researchers. He is best known for inventing the cyclotron, one of the first and most successful "atom smashers." With this particle accelerator, Lawrence and his colleagues were able to make new radioactive isotopes , synthesize transuranium

American physicist Ernest Orlando Lawrence, recipient of the 1939 Nobel Prize in physics, "for the invention and development of the cyclotron and for results obtained with it, especially with regard to artificial radioactive elements."
American physicist Ernest Orlando Lawrence, recipient of the 1939 Nobel Prize in physics, "for the invention and development of the cyclotron and for results obtained with it, especially with regard to artificial radioactive elements."

elements that do not occur in nature, and advance knowledge of the atomic nucleus.

Youth and Education

According to his mother, Lawrence was "born grown up" on August 8, 1901, in Canton, South Dakota, a rural town of less than one thousand inhabitants. Ernest's father, Carl, was superintendent of the Canton public schools when his eldest son was born. A second son, John, was born in 1904. Both boys demonstrated early interest in science and technology and they eventually worked together on medical applications of the cyclotron.

Lawrence graduated from the University of South Dakota in 1922 with a bachelor of arts in chemistry. His original intention had been to become a physician, but as a sophomore he met Lewis Akeley, the university's lone physics professor. Akeley soon recognized the young man's talent and transformed him into a physicist. Although it was at the time impossible to major in that discipline at the university, Akeley provided special tutorials for his prize student and thus prepared him for graduate study.

In 1922 Lawrence entered the University of Minnesota, where he became a research student of W. F. G. Swann and was awarded a master of science in physics. His thesis became the basis for his first publication. When Swann moved to the University of Chicago and then to Yale, Lawrence followed him, earning his Ph.D. from the latter institution in 1925. After his degree he remained at Yale, first as a research fellow and soon thereafter as a faculty member.

The Atomic Nucleus and the Cyclotron

Ernest Lawrence's experimental skill, hard work, and professional ambition were soon common knowledge among many physicists, and offers of employment came from a number of universities. The most attractive was from the University of California in Berkeley, an institution that was eager to build a reputation as a world-class center for scientific research and education. In 1928 Lawrence moved across the country to assume an associate professorship at Berkeley. Two years later he was a full professor, the youngest in the history of the university.

The first quarter of the twentieth century was a time of great intellectual ferment in the physical sciences. Experimental discoveries such as x rays, cathode rays (electrons), and radioactivity demanded drastic revisions in the prevailing concept of atomic structure. There was convincing evidence, largely obtained in European laboratories, that atoms consisted of minuscule, incredibly dense, positively charged nuclei surrounded by negative electrons. The new quantum or wave mechanics, developed by German physicist Max Planck, Danish physicist Niels Bohr, German physicist Werner Heisenberg, Austrian physicist Erwin Schrödinger, and others, appeared to provide the theoretical and mathematical tools to explain this structure. But what was the nature of the nucleus and the forces that held together the positively charged protons that, according to classical electrostatic arguments, should be repelling each other?

It was to such problems that Lawrence soon applied his experimental genius. He was confident that nuclei could be probed by bombarding atoms with protons and other subatomic particles. What was needed was a machine to accelerate these tiny projectiles to high velocities and energies. The design for such a device came to him in the spring of 1929, while reading a paper by Norwegian engineer Rolf Wideröe. The prototype for the "magnetic-resonance accelerator" was built by Niels Edlefsen, Lawrence's first Ph.D. student, in early 1930.

The first "cyclotron," as it came to be known, consisted of a flat glass cylinder containing two semicircular D-shaped electrodes. These electrodes (called "dees") were attached to a radio-frequency oscillator that would cause them to alternate polarity rapidly between positive and negative charges. A strong electromagnet, with 4-inch pole faces above and below the apparatus, created a magnetic field perpendicular to the plane of the electrodes. In operation, the glass chamber was pumped down to a near vacuum and protons (hydrogen ions) were injected into the center of the device. As the dees changed polarity, the positive protons would be alternatively pulled and pushed in a circular orbit of increasing diameter. As the orbit increased, so did the velocity and energy of the particles. When the stream of protons reached the desired energy, they were deflected and directed at the intended target.

The first model cyclotron, a leaky gadget coated with sealing wax that cost about $25, was soon replaced with a brass box. Before long, the size of the device began to grow. The 4-inch version was succeeded by a 9-inch model, followed by cyclotrons 11, 27, 34, 60, and finally 184 inches in diameter. Each increase in size required larger electromagnets, more electric power, and more money. The energy of the accelerated particles also increased, and that was the point of the enterprise—to obtain more powerful probes. At the 11-inch stage, Lawrence and his team "split" their first atom, and the 184-inch cyclotron attained his goal of particles with energies of 100 million electron volts. In all this research, significant contributions were made by Lawrence's students and collaborators at the Radiation Laboratory, especially M. Stanley Livingston and Edwin M. McMillan.

Applications, Issues, and Analysis

In 1939 Ernest Lawrence was awarded the Nobel Prize in physics for his invention of the cyclotron. That same year Austrian physicists Lise Meitner and Otto Frisch correctly concluded that the experimental results of German chemists Otto Hahn and Fritz Strassmann indicated that neutrons cause uranium atoms to split (undergo fission ) into smaller fragments, with the release of great quantities of energy. It was also in 1939 that the German army invaded Poland, launching World War II (1939–1945). With the latter two events, the study of the atomic nucleus and atomic energy literally became a matter of life and death.

Lawrence's 184-inch cyclotron was soon modified to separate uranium isotopes and became the prototype for the calutrons used for similar purposes in the Manhattan Project . Both during and after the war, Lawrence was one of the most politically influential American scientists; he served on many key committees, including the Scientific Panel that advised on the first use of the atomic bomb.

Ernest Lawrence died on August 27, 1958, in Palo Alto, California. Never a gifted mathematician or theoretician, he was a brilliant experimentalist with the entrepreneurial skills to enthusiastically promote his vision of "big science." Thanks to the cyclotron and other accelerators there are hundreds of radioactive isotopes that have applications in medicine and elsewhere, dozens of subatomic particles, and at least seventeen artificial elements that stretch beyond uranium in the Periodic Table. Lawrence's legacy is commemorated in the Lawrence Berkeley Laboratory, the Lawrence Hall of Science, the Lawrence Livermore Laboratory, and, most appropriately, in element number 103 (which concludes the actinide series). Lawrencium (Lr) was the first element named for an American.

SEE ALSO Bohr, Niels ; Heisenberg, Werner ; Meitner, Lise ; Planck, Max ; Radioactivity ; SchrÖdinger, Erwin ; Transactinides .

A. Truman Schwartz

Bibliography

Childs, Herbert (1968). An American Genius: The Life of Ernest Orlando Lawrence, Father of the Cyclotron. New York: Dutton.

Davis, Nuel Pharr (1968). Lawrence and Oppenheimer. New York: Simon & Schuster.

Heilbron, J. L., and Seidel, Robert W. (1989). Lawrence and His Laboratory: A History of the Lawrence Berkeley Laboratory, Vol. 1. Berkeley: University of California Press.

Herkin, Gregg (2002). Brotherhood of the Bomb: The Tangled Lives and Loyalties of Robert Oppenheimer, Ernest Lawrence, and Edward Teller. New York: Henry Holt.



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Julia Gordon-Bramer
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Aug 29, 2016 @ 5:17 pm
Please let me know how I may get permission to use the 1929 picture of Ernest Lawrence and his Cyclotron in a class plan I am putting together to publish. Thank you.

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