Rhyolitic tephra horizons in northwestern Europe and Iceland from the AD 700s-800s: a potential alternative for dating first human impact

The distribution and geochemistry of four rhyolitic tephra horizons from Iceland dated to the ad 700s–800s is assessed. These include the rhyolitic phase of the Landnám tephra (ad 870s), the ad 860 layer, a previously unrecorded tephra called the GA4–85 layer (c. ad 700–800) and the Tjïrnuvík tephra (c. ad 800s). The ad 860 and GA4–85 layers were first found in peat bogs in north Ireland. They are here correlated with equivalent horizons on Iceland which were found below the Landnám tephra (c. ad 870s). This time period is considered important in the North Atlantic region, because it coincides with a phase of human settlement in Iceland and the Faroe Islands. The establishment of a detailed tephrochronology may provide a tool for exact dating of sediment successions and sediments associated with archaeological excavations. Caution must be taken especially on Iceland where the Landnám tephra is often used for dating archaeological sites. This investigation show that several rhyolitic tephra horizons occur close in time to the Landnám tephra, and that mistakes can be made if detailed geochemical analyses are not carried out, especially in areas which are distal to the source of the Landnám tephra (the Veidivötn and Torfajökull volcanic systems, southern Iceland)

Background Components of a Liquid Scintillation Counter in the 14C Window

From the 19th International Radiocarbon Conference held in Keble College, Oxford, England, April 3-7, 2006.We present a broad and detailed study of the background components of a liquid scintillation (LS) detector, using a simple laboratory-built system, ICELS. It was specifically designed for radiocarbon dating and is compact and easily transportable (total weight 35 kg). Its flexible LS detector unit has a dome-shaped vial with 3 mL benzene to which 45 mg butyl-PBD is added. The vial sits on the top of a vertical 28-mm-diameter phototube. The gamma radiation, to which the benzene is exposed under varying conditions, was measured by replacing the vial with a 38-mm-diameter NaI crystal. The pulse-height spectra of the 14C LS background and the NaI gamma background were measured in a surface laboratory and in a deep underground counting room with: 1) a lead shield of varying thickness; 2) lead of normal and low 210Pb concentration; 3) phototubes of 2 different types; and 4) varying benzene volume. The beta emission from the face of the tubes was measured with a low-level Geiger counter.The Radiocarbon archives are made available by Radiocarbon and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

Balanced Window Method in 14C Liquid Scintillation Counting

The authors present a detailed theoretical and experimental study of the liquid scintillation balanced counting method, widely used in radiocarbon dating, using a simple, laboratory-made system. A fixed counting window becomes a balanced window when the high voltage is set where the 14C count rate rises to a maximum. Using a measured 14C pulse height spectrum, we have calculated the lower and upper limits for 11 balanced windows of varying width and their respective counting efficiencies. Furthermore, we have studied: (1) theoretically and experimentally, the counting efficiency for up to a +/15% shift in pulse height from the balanced setting, (2), the change in pulse height due to temperature variations, (3), the long-time stability of the system, and (4), a method that allows a quick determination of the balance voltage for individual samples, using the Compton spectrum of 133Ba. The standard deviation for thirty 24-hr measuring periods for a 14C standard (190 Bq) was within the expected statistical error (0.03%).The Radiocarbon archives are made available by Radiocarbon and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

Underground measurements of radioactivity

International audienc