AMS Radiocarbon Dating: Its Current and Future Role in Art Research
- PDF / 3,270,437 Bytes
- 8 Pages / 576 x 777.6 pts Page_size
- 76 Downloads / 171 Views
A M S Radiocarbon Dating: Its Current and Future Role in Art Research D.C. Stulik and D.J. Donahue Introduction
Since the development of 14C dating by W.F. Libby in the 1940s and 1950s, the method has proved to be the best absolute method for chronometric dating of organic and some carbon-containing inorganic materials.1 It has become an essential research tool for both archaeologists and geologists.2 Even broader application horizons have been opened to radiocarbon dating by use of the accelerator mass spectrometer, which allows routine analysis of submilligram samples. Art curatorship and art conservation directly benefit from this development. There are pronounced similarities between application of radiocarbon dating in archaeology and art research but there are also major differences which make it difficult to simply take a methodology developed for archaeological research and apply it directly to radiocarbon dating of art objects.3 In both fields the application of dating techniques focuses on dating an object of unknown age or cross-checking the age of an object previously dated by other methods. Archaeological dating often takes advantage of newly opened archaeological sites and focuses on the identification of disjunctions, disparities, verification of the specimen association, and assessment of the magnitude of temporal hiatuses between the date and the event.4 Art research more often deals with an object which has been removed from the place of its creation for a long time and for which provenance information is not available or which precipitated questions about its provenance and authenticity. If neither art historical research nor connoisseurship allows plac-
MRS BULLETIN/JANUARY 1992
Cosmic radiation
I I
I I
I I
I I
T
T
T
T
upper atmosphere neutrons
14
N
14,
14
15 km
CO,
Atmospheric mixing
biosphere
Figure 1. Production of 14C and its movement in the Earth's biosphere.
53
AMS Radiocarbon Dating: Its Current and Future Role in Art Research
than on production of civilization periods, such research would benefit from high and ultrahigh precision measurements. Because the majority of art objects are unique, irreplaceable, and relatively small, the ability to date a minimum amount of sample is extremely critical. Radiocarbon Dating The impact of high energy primary and secondary cosmic rays on atoms and molecules of the upper layers of the Earth's atmosphere (lower stratosphere and upper troposphere) causes many nuclear reactions that produce neutrons, protons, aparticles, and other subatomic particles (Figure 1). A large portion of neutrons produced by the cosmic rays are slowed down by collision with atoms in the atmosphere. The resulting thermal neutrons react with 14N (nitrogen atoms) to form a 14C atom and a proton (hydrogen nucleus) through a nuclear reaction: 14
14
C -> I4N + $ + v
The death of the organism sets a time zero (t = 0) on a "radiocarbon clock." The decrease of concentration of 14C in a dead organism follows the exponential radioactive decay law (Figure 2). T
Data Loading...
