February 27 1940 – Carbon-14 is Discovered by Martin Kamen and Samuel Ruben

February 27 1940 – Carbon-14 is Discovered by Martin Kamen and Samuel Ruben
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A pair of men working at the University of California at Berkeley made a startling discovery on February 27, 1940 — one with implications for the future of science in everything from biology to anthropology. The two chemists, Martin Kamen and Samuel Ruben, realized basic the basic element of carbon had a radioactive isotope. Known as “carbon-14” due to its two additional neutrons, the ion exists in all sorts of natural organisms and can be used to estimate the age of materials up to 50,000 years old.

Kamen and Ruben began working together at Berkeley in 1938, operating under the direction of Nobel Laureate Ernest O. Lawrence at the Berkeley Radiation Laboratory. In a bid to understand the movements of carbon through the process of photosynthesis in plants, algae and bacteria, the researchers hoped to use carbon-11 as a sort of flashlight to illuminate the pathway. There was a problem: the element was exceedingly difficult to track.

What the two scientists did know was some nuclear physicists believed in the possibility of a carbon isotope capable of residing in cellular tissue for ages on end. Isotopes — forms of an atomic element that have varying numbers of neutrons — are common throughout nature. In the case of carbon, all of the atoms have six protons and the most prevalent isotope has just as many neutrons. Carbon-11 has one less neutron, five. Carbon-14 has two more, for eight. Because of these subtle differences, the atoms have vastly different radioactive properties: the former has a half life of just 21 minutes, the latter a whopping 5,700-plus years.

Early on the morning of February 27, 1940, Kamen collected the results of a five-day radiation bombardment and took them to Ruben’s desk. Frustrated after a number of disappointing results, the two were surprised Ruben found undeniable proof carbon-14 was putting off radioactive energy. The miniscule charge put off by the atoms made observation and information gathering incredibly challenging, meaning the men had to abandon attempts to experiment with carbon-14 in 1942 essentially before even being able to try.

With the United States government becoming more active as World War II ramped up, Kamen and Ruben took divergent paths. Ruben researched the mechanisms of action for a poisonous gas made with carbon-11, phosgene, and eventually died in a laboratory accident with the material. Kamen, an immigrant from Canada with suspected Communist ties, came under investigation for his left-leaning political views and lost his job with the Manhattan Project in July 1944. Seven years later, he would face accusations in front of the House Un-American Activities Committee and lose his passport. (He would not be to clear his name until the late 1950s.)

In the meantime, Willard Libby, a chemist at the University of Chicago, experimented with carbon-14 further. Through a series of tests, he calculated the atom’s half-life to be approximately 5,568 years, slightly less than the currently accepted measurement (5,730 years) discovered at Cambridge University in 1962. He theorized that, by analyzing the amount of carbon-14 in plant matter, one could form a solid estimate of the item’s age. He continued to refine the concept for the next decade, calculating the age of an ancient Egyptian barge using wood samples. The science of archaeology was revolutionized and, for his efforts, Libby received the Nobel Prize in Chemistry for 1960.

Kamen, on the other hand, would spend the rest of his career rehabilitating his reputation through as series of breakthroughs in bacteriology and photosynthesis. He worked much of his later life as a professor at both the University of California-San Diego and the University of Southern California, eventually receiving the Enrico Fermi Award for advances in science and technology from President Bill Clinton in 1995.

Also On This Day:

272 – Roman Emperor Constantine the Great is born

380 – The Edict of Thessalonica makes Christianity the state religion of the Roman Empire

1870 – Japan adopts its current national flag to designate merchant ships

1922 – The 19th Amendment to the United States Constitution, allowing women the right to vote, is upheld by the Supreme Court in the decision for Leser v. Garnett

1943 – The Rosenstrasse Protest, one of few instances of public opposition to Nazi Holocaust policies, begins in Berlin

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