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Radiocarbon Dating: Samples
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Radiocarbon dating works by precisely measuring the ratio of radiocarbon to stable carbon in a sample. This is done in one of three ways: 1. Gas Proportional Counting, 2. Liquid Scintillation Counting, and 3. Accelerator Mass Spectrometry. The purpose in each of these methods is to determine the ratio of radiocarbon to stable carbon in the sample.
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Radiocarbon dating, statistical analysis, researchers' trained eyes and prior knowledge of events in the area are then used to match new samples with tree-ring chronologies from the same area. Manning and his staff in the lab have used such techniques to verify, for example, the likely origins of a Circle of Rembrandt painting (referring to an elite group of students that worked directly with the artist). He showed that the oak board of the painting came from the same tree as the board of another painting, whose origins are known and which hangs in a museum in Krakow, Poland.
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During 1965-1998, radiocarbon dating in Lund was performed in a conventional laboratory at the Department of Quaternary Geology using two CO2 proportional counters for detection of 14C disintegrations. Dating limit for the equipment was ca 40000 years BP, and the precision for Holocene samples was ± 50 to 80 years. The dating capacity was ca 140 samples/year and around 4200 radiocarbon datings were made during the lifetime of the laboratory. The laboratory was definitely closed 3 March 1998. Sören Håkansson was head of the laboratory from the start to his retirement in 1987 and was succeeded by Göran Skog. Almost from the beginning and during more than 30 years Kerstin Lundahl was technical assistant in the laboratory.
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One of the most controversial examples of the use of radiocarbon dating was the analysis of the Turin Shroud, the supposed burial cloth of Jesus. The shroud itself appears to show a person who was crucified and is an object of some veneration because of its supposed association with Christ. Its history dates back at least as far as the mid 14th century AD. The first photograph of the shroud showed the man as a negative image, a kind of three dimensional picture. This, along with other discoveries, such as the supposed presence of pollen spores from Israel on the cloth have suggested the shroud might be an important and genuine relic. In the 1980s, the Archbishop of Turin gave permission to a group of scientists to date small pieces of fabric sampled from the shroud.
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The use of radiocarbon for dating began some 50 years ago and was based on the detection of the decay of the isotope. Nuclear particle counting techniques determine the 14C activity in a sample. In the last 20 years radiocarbon dating by accelerator mass spectrometry (AMS) has become the preferred method. Indeed, in many cases, especially those involving small or valuable samples, AMS is the only viable method. AMS counts the atoms of the different carbon isotopes directly. It is far more sensitive than the decay counting method.
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The concept of using radiocarbon dating to determine the age of carbon-containing materials was first proposed in the 1950s. For the case of iron-based materials, van der Merwe and Stuiver2 first demonstrated that it was feasible to extract the carbon from different iron-based materials and use it to establish their age using radiocarbon dating. A total of 15 samples of iron-based materials were dated by beta counting at Yale University2,3 using a dependable method to extract carbon from iron utilizing flow-through combustion in oxygen with cryogenic trapping of CO2. These studies showed that in a wide range of cases, the carbon in iron-based materials could be extracted and reliably radiocarbon dated.
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