Libby was born on December 17, 1908, in Grand Valley, Colorado. Between 1913 and 1926, he attended various elementary and high schools, before enrolling as a chemistry major at the University of California in Berkeley in 1927. He graduated from that institution with a B.S. degree in 1931 and a Ph.D. in 1933. While performing his doctoral research, Libby constructed one of the first Geiger-Muller tubes in the United States. This device could detect certain forms of nuclear radiation, and the experience of constructing one prepared Libby for his Nobel Prize–winning research in the late 1940s. After graduation, he accepted an appointment as an instructor in chemistry at the University of California in Berkeley. He advanced progressively up through the academic ranks, attaining the rank of associate professor of chemistry in 1941.
When the United States entered World War II in December 1941, Libby took a leave of absence from the University of California to work with Harold Urey on the Manhattan Project at Columbia University. He assisted the emerging atomic bomb project by investigating more efficient methods for separating the isotopes of uranium. After the war ended in 1945, Libby accepted a position as professor of chemistry at the Institute for Nuclear Studies of the University of Chicago (now the Enrico Fermi Institute for Nuclear Studies). It was there, in 1947, while working with his students, that Libby developed his innovative concept for the carbondating technique, a powerful technique for reliably dating objects as much as 70,000 years old.
He based this technique on the decay of the radioactive isotope carbon-14, contained in such formerly living organic matter as wood, charcoal, parchment, shells, and even skeletal remains, and on the assumption that the absorption of atmospheric carbon-14 (produced by cosmic ray interactions) ceases when a living thing dies. At that point, the radioactive decay clock in the organic matter starts ticking, and the object’s age may be determined by a comparison of contemporary levels of carbon-14 in comparable living organisms or viable organic materials.
In developing his idea, Libby reasoned that the level of carbon-14 radioactivity in any piece of organic material should clearly in of the organism’s death. The real challenge he faced was to develop and operate a radiation detection instrument sensitive enough to accurately count the relatively weak beta-decay events of carbon-14. With a half-life of 5,730 years, carbon-14 (radiocarbon) is only mildly radioactive. Libby and his student colleagues constructed a sufficiently sensitive Geiger counter, and Libby then successfully tested his proposed carbondating technique against organic objects from antiquity that had reasonably well known ages. For example, he successfully carbon-dated a wooden boat from the tomb of an Egyptian king, a sample of prehistoric sloth dung that was found in Chile, and a wrapping from the Dead Sea Scrolls. At the time, his interesting tests demonstrated that carbon-14 analysis represented a reliable way of dating organic objects as far back as at least 5,000 years. He received the 1960 Nobel Prize in chemistry for developing carbon-14 dating, with its many important applications in archaeology, geology, and other branches of science.
Libby summarized his interesting contribution to nuclear technology in the 1952 book Radiocarbon Dating. At the invitation of President Dwight Eisenhower, Libby accepted an appointment to serve as a member of the U.S. Atomic Energy Commission (USAEC). He was a strong advocate of nuclear weapons testing and the use of nuclear energy in national defense. On June 30, 1959, Libby resigned from his second-term appointment as USAEC commissioner to rejoin the University of California as a professor of chemistry at the Los Angeles campus. He retired from UCLA in 1976. Libby died on September 8, 1980, in Los Angeles, California, from complications of pneumonia.
HANS ALBRECHT BETHE (1906– 2005)
