A New Lab for a New Science
|Ernest Lawrence about the time he came to the University of California.|
The initial and rapid growth of the Laboratory depended on the support of philanthropists excited by the prospects that Lawrence announced. Although he contributed much more to the technique of the cyclotron than the germ of its invention, it was as proselytizer and entrepreneur, as ever-confident leader, that he set the pillars of the multidisciplinary Lawrence Berkeley Laboratory. To obtain tithes from foundations, gifts from corporations and individuals, and operating expenses from the University, Lawrence had necessarily to offer projects of various content. In multiplying opportunities for donors he built not only particle accelerators but also a new hybrid science, nuclear science, a combination of physics, chemistry, biology, and medicine.
|The old Radiation Laboratory|
Nuclear science arose from attempts to open a field of physics. The study of nuclear transformations began in 1919 with Ernest Rutherford's discovery of the reaction N14(a,p)017, in which a nitrogen nucleus absorbs an alpha particle and ejects a proton to become an oxygen nucleus. The alpha particles came from the only source then available, naturally occurring radioactive elements. For a decade the few physicists who followed up the discovery had no other tool to penetrate the nucleus and made little progress. An extraordinary natural source, a gram of radium exclusive of its decay products, produces 37 billion alpha particles a second, of which perhaps one in one hundred thousand induces a transformation, too few by far to permit chemical separation and examination of the product. Furthermore, the energies of naturally occurring alpha particles, a few million electron volts (MeV), may only just suffice to bring them through the electrical repulsion of the nuclei on which they fall. Rutherford's group at the Cavendish laboratory in Cambridge discovered that naturally occurring alpha particles induce more transformations the faster they travel. A machine was needed to increase the number and speed of the particles, and the pace of nuclear physics.
The construction of an abundant source of energetic alpha particles would have appeared far-fetched if not impossible and useless before the first world war. In 1927, when Rutherford, as President of the Royal Society, expressed a wish for a supply of "atoms and electrons which have an individual energy far transcending that of the alpha and beta particles from radioactive bodies," the prospect had come within the reach of technology. In the interim the rapidly growing demand for electrical power had caused industry to surmount technical challenges of high-voltage generation and transmission. The experience and apparatus so accumulated supported the work immediately undertaken to realize Rutherford's wish; and the disclosure in 1928 by George Gamow, that quantum mechanics allows easier penetration of nuclei than physicists had thought, further encouraged the quest for high energy. At Cambridge John Cockcroft and E. T. S. Walton used a voltage multiplier designed by Continental engineers around 1919. Merle Tuve at the Carnegie Institution of Washington used the air transformer invented by Nikola Tesla. Robert J. Van de Graaff, who worked briefly in a power plant in Alabama, devised his electrostatic generator as a source of direct-current particles. And Charles Lauritsen exploited the facilities of a high-tension laboratory built by Southern California Edison at the California Institute of Technology. All these methods relied on high potentials difficult to contain.
As Lauritsen's initiative suggests, California was prepared for physics on a big scale in 1930. During the 1920s the California Institute of Technology transformed itself from a trade school to a leading technical university. "Caltech" became a favorite beneficiary of the Carnegie Corporation and the Rockefeller Foundation, whose sustained interest in science also dates from the 1920s. Its laboratories and associated facilities at Mount Wilson Observatory had some of the finest physical apparatus in the United States; and by 1930 the finest apparatus in the United States meant the finest anywhere.
The transformation of Caltech was presided over by its chief executive officer, Robert A. Millikan, who in 1922 won the second Nobel prize in physics awarded to an American. His success as physicist rested on precise measurement of the properties of the electron; as fund raiser and institution builder, on personal contact with local millionaires and foundation officials; as public-relations man, on frank self-promotion and a knack for memorable phrases. This mixture of traits, which was also to characterize the promotion of physics at Berkeley, may be illustrated by the main line of work of Millikan's research group around 1930. The line was study of cosmic rays," the "birth cries of the universe" (both phrases coined by Millikan); its financial backing, local resources and the Carnegie Institution of Washington; its most elaborate method, the examination of tracks left by the rays as they crossed a big cloud chamber exposed to a strong magnetic field. In 1932 this installation gave evidence for the existence of a positive electron, which four years later brought its discoverer, Carl D. Anderson, America's fourth and California's first Nobel prize in physics.
The physicists at the University of California had also enjoyed more than an average share in the growth of American physics since the first world war. Their research facilities had been greatly improved in 1924 with the completion of LeConte Hall, the first physics building at a public American university built and furnished as lavishly as the best at the big private schools. Their departmental research fund rose from nothing to $13,000 a year between 1920 and 1930; though less than what Millikan had from Caltech's endowment, it yet represented a substantial, and growing, commitment of the State to the support of physics. Their staff increased in numbers and improved in quality. The acquisition of one-half of J. Robert Oppenheimer in 1929, the other half going to Caltech, may be regarded as symbol of Berkeley's rapid approach to parity with Pasadena. It remained to develop a counterpart to Millikan.
|U.C. Berkeley campus circa 1940. The Old Radiation Laboratory is the small, house-like structure to the right of the campanile at clock height; Le Conte hall is directly beneath the lab, Crocker Laboratory above it.|
When Ernest Lawrence came to Berkeley from Yale as associate professor of physics in 1928, he planned to continue the work on photoelectricity on which he had begun to build a reputation. But early in 1929 he read about a method for realizing Rutherford's wish for fast particles, saw how to transform it, and started a revolution in physics. The method, demonstrated by the Norwegian engineer Rolf Wideroe in 1928, pushed sodium and potassium ions to a certain energy by an accelerating potential corresponding to only half the energy. The trick was to use the potential twice: the ions were pulled into one end of a tubular electrode and pushed from the other by an electric field that had meanwhile reversed direction. Wideroe chose the length of the electrode so that the field would have to change with radio frequency, and he observed that it might be applied to a series of electrodes to accelerate particles to whatever energy one pleased. Each electrode would have to be longer than its predecessor to maintain resonance; to achieve high energy with light ions would require a very long machine.
Lawrence recognized the value of the method for heavy ions. For the alpha particles of interest in nuclear physics, however, Wideroe's accelerator would have been prohibitively expensive. Would it be possible to collapse the apparatus by forcing particles to pass the same electrode repeatedly? Lawrence thought to recycle the particles by bending their paths in a magnetic field perpendicular to the plane of their orbit, and to accelerate them twice a turn. As they gain energy and velocity, they move into a wider orbit; and only if the increase of their velocity and the enlargement of their path compensate, so as to make the interval between successive accelerations constant, would the device have any promise. According to a fundamental proposition of electrodynamics, the centripetal acceleration of a particle of charge e and velocity v in a magnetic field B perpendicular to the motion is evB/c, where c is the velocity of light. Equating this expression with that for mechanical centrifugal force, mv2/r, m the particle's mass and r the radius of its orbit, Lawrence observed with surprise and delight that the frequency of a cycle, v/2¼r, is eB/2¼mc, independent of the size of the orbit.
|Lawrence's handwritten description of Wideroe's method for accelerating ions.|
To produce an alpha particle or hydrogen-molecule ion at one MeV with a moderate magnetic field of, say, 5000 gauss, Lawrence needed an electric field that alternated with a frequency of about 4 million cycles per second (4-106 Hertz). That lies in the region of short radio waves. The technology of high-power vacuum-tube oscillators for radio transmission had greatly advanced during the 1920s, and Lawrence, a skilled amateur operator, knew their uses and designs. Like the high-potential machines of Cockcroft-Walton, Tuve, Van de Graaff, and Lauritsen, Lawrence's low-potential cyclotron would not have been possible without then recent industrial development. In his case the oscillator tubes and circuits associated with commercial radio, which allowed him to escape the pitfalls of high potential, were decisive.
The first successful cyclotron, built by Lawrence and his graduate student M. Stanley Livingston, accelerated a few hydrogen-molecule ions to an energy of 80,000 electron volts. Since each ion received an accelerating kick twice in a circuit as it entered and left the single flat semicircular electrode or "dee," those that managed to reach full energy and fall into the collecting cup 4.50 cm from the center of the instrument had made no fewer than forty turns. The result, reported to the American Physical Society meeting in January 1931, earned Livingston his Ph.D. and Lawrence $500 from the National Research Council towards the construction of a machine that might be useful for nuclear physics.
Their main problem was to assure that the particles stay away from the walls of the dee during the many revolutions necessary for acceleration. Lawrence and Livingston bent the electric field lines and hence the paths of the particles toward the central horizontal plane of the cyclotron by placing a grid across the entrance to the dee. They achieved a small beam. An even larger one appeared, however, when Livingston tried a run without the shielding grid. The current reached a billionth of an ampere, about the number of alpha particles emitted each second from a gram of radium. The net electric forces at the mouth of the dee bow inward; their net effect on an accelerating particle is to push it back toward the desired plane.
A similar agreeable surprise occurred in 1931, after Livingston had taken great care to make the pole faces of a new magnet give a uniform field. Again it turned out that natural inhomogeneity in the field improved the strength of the beam. Lawrence and Livingston learned that thin, soft iron shims greatly encouraged the beam when placed between the wall of the vacuum tube and the magnet so as to make the total magnetic field decrease with distance from the cyclotron's center. The magnetic flux bulges outward and particles moving out of the central plane experience an increasingly large force pushing them back. The empirical discovery of the focusing exerted by unshielded electric and shimmed magnetic fields made possible cyclotron beams with useful intensities.
To obtain beams with useful energies, Lawrence required more powerful oscillators, a larger tank, and above all, a bigger magnet. The rapid pace of radio technology again helped. While Lawrence was studying the design of several large and expensive magnets, he learned that a huge magnet yoke stood idle at Palo Alto. The white elephant had been made by a local firm, the Federal Telegraph Company, for use in a method of radio transmission made obsolete by the vacuum tube. Lawrence was able to secure the yoke through Leonard T. Fuller, professor of electrical engineering at the University, who was also a vice president of Federal.
The gift came as it was, eighty tons of metal fifty miles from Berkeley. How would Lawrence get it home, and where would he put it? Who would pay to convert it for use in a particle accelerator? Lawrence appealed to Frederick Cottrell, a chemist formerly with the University, who had set up the philanthropic Research Corporation of New York on royalties from industrial use of a method of smoke precipitation he had invented. Lawrence hinted that the cyclotron might be useful for high voltage x-ray technology as well as for nuclear physics; the Research Corporation made available $5000, and its president, Howard Poillon, secured $2500 from the Chemical Foundation to move and equip the magnet yoke. During August 1931 Robert Gordon Sproul, president of the University, agreed to house the magnet and to pay for the power to run the cyclotron.
The Rad Lab, the forerunner of the present Lawrence Berkeley Laboratory, arose from the skillful mobilization of science, technology, philanthropy, and the University. To keep the Laboratory going and growing in the next decade, Lawrence would have to return again and again to these resources, and to expand them. The timing might not appear propitious. The Rad Lab came into existence as the country was sliding into the depths of the Great Depression. Lawrence could have read in the business section of Time for the last week in September that the first quarter of 1931 bid fair to be the worst period ever in American financial history. By any measure -- available electric power, tax receipts, balance of payments, housing starts, idle steel capacity -- the country was scraping bottom. Hiring froze at many universities and at the big industrial research laboratories; foundations cut back commitments; the number of fellowships declined. Not until 1935 did the profession as a whole resume its growth. Lawrence set up a new laboratory at the nadir of the world's finances.
|Early cyclotroneers (left to right): J. J. Livingood, F. Exner, M. S. Livingston, D. Sloan, Lawrence, M. White, W. Coates, L. J. Laslett, T. Lucci.|
Against the dire circumstances of the early 1930s Lawrence's optimism, even boosterism, engaged the willing belief of ordinary people sick of Depression. He staffed his laboratory with graduate students and junior faculty of the physics department, with fresh Ph.D.s willing to work for anything, and with fellowship holders and wealthy guests able to serve for nothing. He and they created an environment of enthusiasm, congeniality, collegiality, and technical competence. There really was little money, despite Lawrence's success at grant gathering; while the machines consumed tens of thousands, and then hundreds of thousands of dollars, the staff made do with small salaries, if any, and none of the fringe benefits now common: medical insurance, secretaries, and paid travel to meetings.
Lawrence's machines and entrepreneurship succeeded first with physicists and chemists and their supporters. He wondered where his new science belonged. "Shall we call it nuclear physics or shall we call it nuclear chemistry?" He next found backers in the life sciences, whom he approached around 1935, as the Depression began to lift. The biggest of the Berkeley cyclotrons of the 1930s was built for "nuclear medicine." The hybrid, nuclear science, arrived to effect the advancement that none of its constituent disciplines could achieve alone.