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1940: Immigrant Sons Make Biochemistry Breakthrough

Martin Kamen and Sam Ruben identify the isotope carbon-14, making it possible to date artifacts.

David Green
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A mammoth tusk found in Taimyr, Russia: Thanks to the discovery of carbon-14 dating, we can know how old it is.Credit: Reuters
David Green

On February 27, 1940, the physicists Martin Kamen and Sam Ruben made the first identification of the isotope carbon-14 in a laboratory at the University of California, Berkeley. The discovery not only made it possible for archaeologists and others to date artifacts containing organic material, but, even more essentially, the use of carbon-14 as a radioactive marker transformed the study of a wide variety of biochemical processes.

Nearly all of the carbon naturally occurring in the universe is carbon-12, a stable atom with six protons and six neutrons. Carbon-14 (six protons, eight neutrons) is a naturally occurring isotope, but one that is present in matter in a fixed ratio of one part per trillion. Because of its known proportion, and because it has a fixed rate of radioactive decay, with a half-life of 5,730 years, it can be used to determine the age of items containing carbon, and can also be used as a marker to follow the progress of carbon in chemical or biochemical reactions.

It was chemist Willard Libby who, in 1949, devised the method used in radiocarbon dating (work for which he won the Nobel Prize in 1960), but Kamen and Ruben’s discovery was no less important. Ruben died in 1943, and Kamen lost nearly a decade in his career when he was blacklisted for nonexistent political crimes. Sam Ruben was born Charles Rubenstein in 1913 to Jewish-Russian immigrant parents in San Francisco. A talented boxer and basketball player growing up, he received his Ph.D. in chemistry at Berkeley in 1938. It was in the radiation lab there run by Ernest Lawrence that Ruben met Kamen, and began their joint search to find a radioactive marker that would help identify the source of the oxygen produced during photosynthesis.

Kamen was born in 1913 in Toronto, and grew up in Chicago; he was also the son of Jewish-Russian immigrants. Kamen’s education was at the University of Chicago; after receiving his Ph.D. there in physics, he began working in Lawrence’s lab.

Following his and Kamen’s crowning discovery in February 1940, Ruben went on to study phosgene, a poisonous gas, for the War Department. He died on September 28, 1943, a day after being accidentally exposed to it.

Kamen got into trouble in 1945 after attending (and playing viola at) a party at violinist Isaac Stern’s home in San Francisco. It was there he met two Russian diplomats, one of whom asked him for help in attaining radiotherapy for a friend with leukemia. When he was later observed having dinner out with the diplomat, Kamen was immediately fired by Berkeley. This made him untouchable by any other university, until Arthur Holly Compton hired him to run the cyclotron at the medical school of Washington University, St. Louis.

Kamen only succeeded in fully clearing himself – and receiving a passport so he could travel – in 1955, when he sued the Chicago Tribune after it described him as a Soviet spy. First, however, he tried killing himself in despair. In his 1985 autobiography, Kamen described how he had tried slitting his throat. “Fortunately,” he wrote, “the knife I had seized had been dull.”

Kamen later went on to hold positions at Brandeis University and the University of California, San Diego, where he was a member of the founding faculty in 1961. He died in Santa Barbara, California, on August 31, 2002, at age 89.