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However, in the case of sites that are no longer excavated, the sample should be selected preferentially according its proximity to the preserved (available) sections.The alpha contribution from the sediment or the external tissues in contact with the enamel can be easily suppressed in the laboratory by removing at least 20 µm from both sides of the enamel layer.Consequently, we advise that the tooth should be collected with at least 150 g of its embedding sediment. It can be done either by inserting TL or OSL dosimeters, which will record the gamma dose rate for at least several months, and/or using a portable gamma spectrometer, which can provide rapid dose rate measurements (in 10 to 30 min).Both kinds of measurements should be done at a 30 cm horizontal depth within the targeted stratigraphical unit, in order to make sure that only the radioactivity of the sediment is recorded.In contrast, the dose rate is evaluated by measuring the radioactivity in the tooth itself (in all the dental tissues constituting the tooth, i.e.enamel, dentine and, sometimes, cement) and in its surrounding (sediment, rocks, etc.).
Around 100-150 g of sediment are usually required for HRGS analyses, whereas only a few grams are needed for ICP-MS analyses.The sediment sample must be wrapped in a plastic bag and sealed with tape to avoid a dry out in order to ensure a correct evaluation of its water content (in weight %); measurement of radioactivity and to derive the external gamma dose rate.