Willard F. Libby

Born: December 17, 1908Birthplace: Grand Valley, ColoradoDied: September 8, 1980Place of death: Los Angeles, CaliforniaAmerican chemist Libby postulated that the radioactive isotope of the element carbon, those atoms having a mass number 14, is incorporated into living matter at a steady rate until its demise. He developed an ultrasensitive device for the detection of the disintegration of this radioactive isotope. Building upon the newly determined half-life of carbon 14, he was able to create, for the first time, a reliable measure of the age of archeological materials. By numerous experiments he established the validity and extended the useful range of his method.Areas of achievement Chemistry, science

Early Life

Willard F. Libby, the son of Ora Edward and Eva May (née Rivers) Libby, was born in Grand Valley, Colorado. The family moved to an apple ranch near Santa Rosa, California, in 1913. Sources disagree about the location of his primary education. His Nobel Prize biography states that he attended a small local school before graduating from the Analy Union High School near Sebastopol, California, in 1926. Libby entered the University of California, Berkeley, in 1927 and, after an earlier interest in mining engineering, he focused instead on chemistry, receiving his B.S. in 1931 and his Ph.D. in 1933.

Libby remained at Berkeley, beginning as an instructor in chemistry, and rose to associate professor in 1941. During this time he engaged in research with neutrons, low-energy radioactive elements, and the gaseous state. These areas led to his most important contribution, radiocarbon dating . Within the first two years of his independent research Libby had developed a sensitive Geiger counter capable of detecting very low levels of radiation.

Libby was conducting research at Princeton University (1941), on a sabbatical leave sponsored by the Guggenheim Foundation, when the United States entered World War II. He joined Harold C. Urey (Nobel laureate in chemistry, 1934) at Columbia University. Together, as a part of the Manhattan Project , they developed the gaseous-diffusion approach to isolate the uranium isotope of mass 235, which led ultimately to the successful development of the atomic bomb.

Life’s Work

In 1945, Libby moved to the University of Chicago to work at the Institute for Nuclear Studies, which was directed by Enrico Fermi (Nobel laureate in physics, 1938). Libby’s early training and research had prepared him for the work that earned him the 1960 Nobel Prize in Chemistry. He had studied the radioactivity of elements that produced only low energy levels of emissions. He had also examined the elements as they exist in the gaseous state.

As soon as Libby began to design independent research based on his own ideas, he built a Geiger counter that was shielded from cosmic rays. Some reports show the counter had lead shielding, and others show it had iron shielding. However, in his Nobel lecture Libby describes the apparatus as having an eight-inch iron shield. Even such careful protection was insufficient to prevent natural cosmic rays from overshadowing the weak radiation being observed. Libby and his students responded by devising an electrical arrangement that was capable of interrupting the counter for one-thousandth of a second when the external radiation reached a prescribed amount. This procedure allowed for precise measurements.

The chief source of Libby’s genius was his ability to absorb and synthesize the recently published facts concerning radioactive nuclei. In 1939, Serge Korff had discovered that carbon atoms of mass 14 are produced when the nitrogen of the atmosphere is bombarded by neutrons generated by cosmic rays interacting with air in the upper atmosphere. In 1940, Martin Kamen showed that the half-life of carbon 14 is 5,730 years. All radioactive atoms are constantly decomposing to more stable atomic arrangements. The half-life of a given element is the time required for the intensity of a particular sample to become half as intense. Thus, a sample of carbon 14 that shows radioactive emission of 100 counts per second (cps) will show 50 cps 5,730 years later and 25 cps after 11,460 years.

Scientists have known for some time that living plants use carbon dioxide to grow, and that Earth’s atmosphere quickly converts carbon to carbon dioxide. Libby reasoned that carbon dioxide containing the heavy, radioactive isotope of carbon with atomic mass 14 should be taken up by living matter along with normal carbon dioxide, which contains the carbon of atomic mass 12. As long as the organism is alive there should be a constant amount of the radioactive carbon in its cells. This occurrence also should maintain a constant ratio between the carbon dioxide coming in and the carbon 14 decaying. Once the organism dies, however, no fresh carbon dioxide of either mass would be incorporated and the remaining radioactive carbon (mass 14) should begin to disappear. In one half-life, or after 5,730 years, the organism should have half as much radioactivity as was present at the time of its demise.

To use his method Libby had to test the assumption that the level of radioactivity present in organic (living) matter is constant around the globe. He tested samples from many sources, and he showed that the place of origin caused no change in the intensity of radioactive emissions from the carbon 14.

Using his ultrasensitive apparatus, Libby sought to determine the age of organic matter whose age was already known from independent sources. He began with wood samples from trees, whose age could be determined by counting their rings. The ages were nearly identical by ring counting and radiocarbon dating. With this success Libby tested the wood from the funeral boat of the Egyptian pharaoh Sesostris III. Since the date of the king’s death is historical fact it could be determined that the boat was built about 3,750 years ago. Libby determined that the boat’s wood was 3,261 years old, an astonishingly small difference of less than 3.5 percent.

Over the years Libby modified and perfected his method. For example, in the 1960’s he found that tree ring analysis showed systematic fluctuations in the carbon 14 content of the atmosphere and resulted in a recalibration of the timescale used. He also studied the radioactive isotope of hydrogen called tritium. This element was used to date water samples enriched in tritium after testing the hydrogen bomb in 1954.

Libby played significant political roles when he took a leave from the University of Chicago in 1954 to serve on the Atomic Energy Commission (AEC). His conservative view and his strong opinions concerning the balance between the risks of being poorly armed and the risks of testing atomic weapons earned him a great deal of criticism during the Eisenhower presidency.

Libby left the AEC in 1959 and was awarded the Nobel Prize in Chemistry in 1960. He served as director of the Institute of Geophysics and Planetary Physics at the University of California, Los Angeles, until his retirement in 1977. He died three years later in Los Angeles at the age of seventy-one.

Significance

Few Nobel Prize-winning achievements in the sciences have directly touched such a broad range of fields as has Libby’s discovery of carbon 14 dating. The ability to date, with reasonable accuracy, prehistoric artifacts opened new vistas for archaeology, anthropology, history, geography, and geology. The appreciation of the interrelationship of cultures was placed on a much more solid foundation.

Libby’s pioneering work also has led to the development of a variety of related techniques, extending the periods of time that can be studied. In his Nobel lecture, Libby expressed the hope that learning more about human ancestors will reveal something about the future of humankind.

Bibliography

Burleigh, R. “W. F. Libby and the Development of Radioactive Dating.” Antiquity 55 (1981): 96-98. Presents the essence of Libby’s scientific accomplishments in language understandable by those without technical training. Special attention is devoted to the expansion of the basic hypothesis to a range of techniques that cover a broad timescale.

Chemistry, 1942-1962. River Edge, N.J.: World Scientific, 1999. A 710-page collection of speeches by Nobel laureates in chemistry, including Libby. Also includes biographies of the prize recipients.

Maschner, Herbert D. G., and Christopher Chippindale, eds. Handbook of Archaeological Methods. Lanham, Md.: AltaMira Press, 2005. A massive two-volume guide to the methods of archaeology, with a chapter on radiocarbon dating. Written for advanced students.

Renfrew, Colin. Before Civilization: The Radiocarbon Revolution and Prehistoric Europe. New York: Knopf, 1973. A well-written description of the entire field exploring prehistoric Europe, providing a detailed analysis of Libby’s contribution.

Shuman, R. Baird. “Willard Frank Libby, 1960.” In The Nobel Prize Winners: Chemistry, edited by Frank N. Magill. Vol. 1. Pasadena, Calif.: Salem Press, 1990. An excellent introduction to Libby’s life and work, written for nonspecialists. Focuses on the awarding of the Nobel Prize and the reaction of the world’s press. Good references for further reading.

Simmons, John. “Willard Libby and Radioactive Dating, 1908-1980.” In The Scientific One Hundred: A Ranking of the Most Influential Scientists, Past and Present. Secaucus, N.J.: Citadel Press, 1996. Ranks Libby eighty-ninth of the hundred most important scientists of all time. A brief, but surprisingly informative presentation of his life and work. Does an excellent job of presenting both the science and Libby’s role in political circles.

Taylor, Royal Erwin. Radiocarbon Dating: An Archaeological Perspective. New York: Academic Press, 1987. A clearly written, detailed description of the entire field of archaeological dating. Libby read parts of this book before his death. The treatment of his work is especially thorough. Extensive index.