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Hofstadter, Robert

Robert Hofstadter

American nuclear physicist Robert Hofstadter (1915–1990) won the Nobel Prize in Physics in 1961 for his pioneering work that unveiled the structure and composition of atomic neutrons and protons. Based primarily at Stanford University, Hofstadter was the first to discover that atomic particles have definite shapes and sizes. Specifically, his studies pinpointed the distribution of charge and magnetic moment in the nuclei of atoms. His scientific work produced useful applications in medicine, astronomy, military defense, and other fields.

Precocious Student

Hofstadter was born in Manhattan, New York, on February 5, 1915. His parents were Louis Hofstadter, a salesman who also owned a cigar store, and Henrietta Koenigsberg. Young Hofstadter was educated in the New York public school system and showed an early aptitude for mathematics. He also harbored a deep love of nature and collected insects, rocks, and leaves. As a young man he developed a lifelong interest in photography. At City College of New York, Hofstadter was influenced by physics and mathematics stalwarts Irving Lowen and Mark Zemansky. He was elected to Phi Beta Kappa and graduated magna cum laude with a bachelor's degree in science in 1935, at age 20. That year, he was also awarded the prestigious Kenyon Prize in Mathematics and Physics.

Hofstadter would not have been able to afford graduate school if he had not been awarded a Charles A. Coffin Foundation Fellowship by the General Electric Company. He attended Princeton University, where he earned a master's degree and a Ph.D. in physics. At Princeton, he quickly became involved in research in physics, including studies of the infrared spectra of organic molecules and of a new type of mass spectrometer. He also studied quantum mechanics.

In his second year of graduate school, Hofstadter became an aide to E.U. Condon, the author of a classic textbook on atomic physics. Condon was a major influence on Hofstadter. But Hofstadter soon joined the infrared laboratory of R. Bowling Barnes. Colleague Robert Herman, in a foreword to a volume of collected works by Hofstadter, describes how he and Hofstadter worked at night to avoid the disruptive power surges that plagued the building during the day, when other machinery was plugged in. Both of Hofstadter's mentors, Condon and Barnes, left Princeton, and Hofstadter finished his Ph.D. on his own. His thesis on oxygen–hydrogen spacing in certain acids, helped elucidate the nature of hydrogen bonding.

In the summer of 1938, Hofstadter worked under Frederick Seitz, a colleague of Condon and Barnes, at the General Electric Laboratory. There, he studied the photoconductivity of zinc silicate or willemite, an element that was being used in the development of television. For the 1938–1939 academic year, he returned to the infrared laboratory at Princeton, working with Herman on further studies of willemite. The two discovered that the fluorescent compound contained crystal currents. The work established a theory of "deep traps" in crystals and would lead to further discoveries in Hofstadter's later work in solid–state physics.

Aided War Effort

After graduating from Princeton, Hofstadter's next stop was the University of Pennsylvania. Seitz, who had taken a faculty position there, invited Hofstadter to work with him, and Hofstadter was given a Harrison Fellowship to study solid–state physics. But Hofstadter actually joined a different group at University of Pennsylvania, working on nuclear physics under Louis Ridenour instead. It was at this time that Hofstadter became friends with Leonard Schiff, a man whom he would later collaborate with.

After the United States entered World War II, Hofstadter went to work for the National Bureau of Standards, hoping to help the war effort by working on an optical proximity fuse with colleagues Joseph Henderson and Seth Neddermeyer. This fuse was used to detonate anti–aircraft and artillery shells. Hofstadter soon left the bureau and joined the Norden Company, working on a radio altimeter. He developed an automatic altitude sensor for aircraft, and helped test it by flying planes himself at low altitudes. The device enabled war planes to fly under enemy radar.

During the war Hofstadter married Nancy Givan, whom he had met while at the University of Pennsylvania. Among other things, they shared a love of jazz. Hofstadter had long collected jazz recordings and had seen shows at the famed Apollo Theater in Harlem. The Hofstadters eventually had three children: Douglas, Laura, and Mary. His son became a physicist and a science writer, winning the 1980 Pulitzer Prize in non–fiction. Laura became a medical writer.

Back at Princeton after the war, Hofstadter became an assistant professor in the department of physics and astronomy. He started work on detecting gamma rays for the Princeton cyclotron. He built on work by German scientists and his own knowledge of solid–state physics to develop a gamma ray detector that used activated alkali halides, in particular sodioum iodide with a minute amount of thallium. In 1948, he got a patent for this radiation detection method, known as a scintillation counter. In 1950, he demonstrated how gamma ray spectroscopy could be done with his patented detection technique.

Pioneered Work at Stanford

In 1950 Hofstadter left Princeton to take a position as associate professor at Stanford University. There he worked with Jack McIntyre, using the scintillation counter he had developed to detect X rays, neutrons, electrons, and other subatomic particles. Then, using an advanced electron accelerator that Stanford possessed, Hofstadter began his pioneering work on studying the structure of the nucleus in atoms. Electron–scattering experiments soon became his primary research target. His goal was to measure the size and thickness of atomic nuclei. He quickly realized he needed much larger equipment to do the research well. To aid in his work, he developed a heavy magnet for a magnetic spectrometer with support from the Office of Naval Research. To precisely position the magnet for studying beams of electrons, he used a U.S. Navy anti–aircraft gun mount.

His first experiments were on gold and polyethylene. Hofstadter quickly realized he needed an even bigger and more powerful magnet. Undeterred, Hofstadter designed a huge new 30–ton magnet, which was built for him by Bethlehem Steel. Along with a ten–ton shield, the magnet was mounted on a much bigger Navy anti–aircraft gun mount. Using his new device, Hofstadter was able to study nuclei of various materials in greater detail. Eventually, Hofstadter designed yet another double–focusing spectrometer, weighing more than 200 tons.

Hofstadter's studies changed radically what scientists knew about the constituent parts of atomic nuclei. Before his research, the constituents of atoms—protons, neutrons, and electrons—were thought to have no structure. He discovered that these elements have definite size and structure and he was able to determine their shapes and sizes, giving the first accurate portrait of the inside of atomic nuclei, which contain almost all the matter and energy of the universe. During this time Hofstadter conceived the idea for a huge electron accelerator. He established a study group that designed the Stanford Linear Accelerator Center and the construction of a two–mile–long accelerator. In this period Hofstadter and his group at Stanford had almost a monopoly on doing research on nuclear structures, because no places outside of Stanford had both the vision and the equipment to do so. It was a rare moment in modern science in which a small group of researchers could succeed in doing what later came to be called "big science."

Nobel Prize and Other Honors

In 1958 Hofstadter was elected to the National Academy of Sciences and became a Guggenheim Fellow. The following year he was named California Scientist of the Year. Later he received the U.S. National Medal of Science. Throughout his career, he worked for the U.S. government in a variety of capacities. In the early 1950s he worked for the Atomic Energy Commission, developing ways to use radiation techniques to measure the contents of a closed suitcase or crate, an early version of anti–terrorism detection methods. He later consulted on many technological problems for the military.

During 35 years of teaching at Stanford, Hofstadter frequently taught large freshman lecture classes on physics and was one of the most popular instructors on campus. He was a staunch advocate of academic freedom and human rights. He was also active in opposing the Vietnam War. He and his family established themselves on a 700–acre ranch in the coastal foothills near Flournoy, California, raising cattle, keeping horses, and nurturing a 40–acre grove of olive trees.

In 1961 Hofstadter won the Nobel Prize in physics, sharing it with Rudolf Mossbauer. The prize committee noted that Hofstadter had revealed the structure of nuclei and atoms and that he had overcome so many physical obstacles in ingenious ways. The panel also lauded the precision of Hofstadter's work and noted: "You have achieved this precision by improving unrelentingly your methods and equipment in the course of time." Biographer William A. Little noted the way Hofstadter approached problems by thinking outside the box: "He thought nothing of proposing a cryostat a thousand times larger than had ever been considered before, just as he had proposed a two–mile accelerator. . . . The engineering challenges that would have to be overcome to accomplish these aims never discouraged him."

Hofstadter did not play a big role in the Stanford Linear Accelerator Center once the idea had been established. That was due primarily to disagreements about the role of government funding and university rights to research. In the tradition of the individual investigator, Hofstadter resisted the measures of government and university control that accompanied the rise of big projects in nuclear physics and other sciences.

The "Crystal Ball"

In the 1960s and beyond Hofstadter turned his attention to new research in nuclear physics. One area was the precise measurement of high–energy gamma rays using large crystal detectors. As with his other research, Hofstadter was not deterred by the size of the equipment needed. He developed a new technology for making very large crystals of high clarity and using new kinds of scintillation counters to form and detect them. Among other things, his work with detectors for high–energy physics led to the development at Stanford of the "Crystal Ball," a detector made with 732 crystals using Hofstadter's sodium iodide compound that he had developed earlier in his career.

Hofstadter worked again with the U.S. government on gamma ray detectors, using the principles he had already developed. Hofstadter was one of the principal investigators for the National Aeronautics and Space Administration program known as the "energetic gamma–ray technology experiment telescope." His concept led to the creation of gamma–ray spectroscopy on orbiting satellites as a way of studying the nuclear physics of objects in space. Earlier, he had tried but failed to interest NASA in using X–ray detectors to explore the galaxy known as the Crab Nebula. Soon after, others were doing exactly what Hofstadter had envisioned.

From outer space to inner space, Hofstadter also worked with Stanford's medical school on a method of using cardiac angiography with synchrotron radiation. It is a minimally invasive procedure that involves the injection of a small amount of iodine to provide images of the arterial system of the heart without bone or tissue mass blocking the view. This was one of many contributions Hofstadter made to practical applications of nuclear medicine, including techniques for using crystals to monitor the brain or other body parts in what is known as positron–emission tomography.

In the early 1970s Hofstadter became interested in the possibility of using nuclear fusion to produce safe, non–polluting energy. He became executive scientist at KMSF Fusion, a pioneering laser fusion company in Michigan. In 1974, under Hofstadter's direction, KMSF was the first place in the world to use lasers to produce fusion in a pellet, and briefly it became the most advanced laser–fusion laboratory in the world. Hofstadter lobbied the United States Congress and private sources for funding the company's efforts, but opposition by federal weapons laboratories caused the company to fail.

In an introduction to Hofstadter's collected works, his colleague Robert Herman noted that a cornerstone of Hofstadter's philosophy was "that beauty and simplicity was at the core of all great science." The satellite carrying his gamma–ray telescope was finally launched aboard the space shuttle Atlantis just a few months after Hofstadter's death in 1991.

Periodicals

New York Times, November 17, 1990.

Online

"Foreword to the Collected Works of Robert Hofstadter," Stanford University, http://www.stanford.edu/dept/physics/people/faculty/shorts/hofstadter–BIO.html (January 2, 2005).

"Hofstadter, Robert," Brittanica.com http://www.britannica.com/nobel/micro/273–80.html (January 2, 2005).

"Robert Hofstadter," National Academy of Sciences,http://stills.nap.edu/html/biomems/rhofstadter.html (January 2, 2005).

"Robert Hofstadter –Biography," Nobel Prize Website,http://nobelprize.org/physics/laureates/1961/hofstadter-bio.html (January 2, 2005).

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Hofstadter, Robert

Hofstadter, Robert (1915–90) US physicist. He proposed that protons and neutrons have a positively charged core surrounded by a cloud of elementary particles (pions). Hofstadter shared the 1961 Nobel Prize in physics.

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