Radiocarbon Dating at the British Museum -- the End of an Era

Article excerpt

The origins of the British Museum's radiocarbon dating laboratory, which closed in 2001, can be traced back to 1948, the year before the first radiocarbon dates were published by Willard Libby and colleagues. To mark its passing, the history of the laboratory was excavated from the Museum's archives and is set within the context of the early days of Libby's research to develop the dating method in the late 1940s that led to him being awarded the Nobel prize for Chemistry in 1960.

After the United States entered World War II following the bombing of Pearl Harbor, Libby had worked on the Manhattan Project, the key aim of which was to develop the atomic bomb. However, he had continued a former interest in `radiocarbon', the name he coined for the weakly radioactive isotope of carbon with atomic weight 14 (hence its other frequently used names `carbon fourteen' or C-14). It is surprising to realize that in the early 1940s it was not known whether or not radiocarbon might exist in nature and whether it had a very short half-life or a longer and thus more useful one. In 1941, for example, the half-life was calculated to be between 1,000 and 100,000 years, interesting information, but hardly usable: it was not until the period 1946 to 1949 that measurements consistently in the region of 5000-7000 were being published (see Libby 1952: 34, table 4). Libby appears to have kept his interest in pursuing the possibility of using radiocarbon for dating reasonably quiet in case it came to nothing, but in late 1946 it became known, indirectly, to Ambrose Lansing, an Egyptologist and then the Director of the Metropolitan Museum, New York (Taylor 1987: 153). This resulted in the first set of unsolicited samples sent to a radiocarbon laboratory, one being a substantial piece of acacia wood from the tomb at Sakkara of Zoser, a third-dynasty Egyptian pharaoh (sample C-1, Libby 1952: 70). This was premature. Although radiocarbon had been produced artificially and its existence in living organisms had been predicted (Libby 1946), it was not until 1947 that Libby's team first detected natural radiocarbon using a sample of methane gas from the sewage works in Baltimore, Maryland (see Taylor 1987: 153; Anderson et al. 1947). However, to detect the radiocarbon level above background count rates considerable sample processing was necessary to enhance the radiocarbon content (isotopic enrichment).

At the end of the War, Libby had taken up a position in the Institute for Nuclear Studies at the University of Chicago. When additional funds were needed to pursue his research on dating, the Viking Fund, Inc., (subsequently known as the Wenner-Gren Foundation for Anthropological Research) came to the rescue, providing the very princely sum of $35,000 for the years 1948-1950 inclusive (Libby 1952: Preface). What proved to be only the first tranche of money, $13,000, was requested by letter on 31 October 1947 and a cheque for that sum was sent by the Fund on 5 November (Marlowe 1980). Would that grant applications always had such simplicity and turnaround time today. An invitation for Libby to speak directly about his work to archaeologists also followed with a lecture in January of 1948 to the Viking Fund Supper Conference. We now take for granted collaboration between radiocarbon scientists and archaeologists, but, based on letters and taped interviews, Marlowe (1980) gives a fascinating insight into some of the difficulties encountered during this period of first interaction.

Following on from the success of first detecting natural radiocarbon, Libby's laboratory worked on perfecting the production and counting of solid carbon, in particular using electronic methods (anti-coincidence counting) to reduce the background count-rate, thus avoiding the need for isotopic enrichment. The Egyptian acacia wood submitted by Lansing was the first ancient sample to be counted, producing a radiocarbon activity in good agreement with its expected activity based on its historical age. …