Biological/Biomedical Accelerator Mass Spectrometry Targets. 1. Optimizing the CO2 Reduction Step Using Zinc Dust

Biological and biomedical applications of accelerator mass spectrometry (AMS) use isotope ratio mass spectrometry to quantify minute amounts of long-lived radioisotopes such as 14C. AMS target preparation involves first the oxidation of carbon (in sample of interest) to CO2 and second the reduction of CO2 to filamentous, fluffy, fuzzy, or firm graphite-like substances that coat a −400-mesh spherical iron powder (−400MSIP) catalyst. Until now, the quality of AMS targets has been variable; consequently, they often failed to produce robust ion currents that are required for reliable, accurate, precise, and high-throughput AMS for biological/biomedical applications. Therefore, we described our optimized method for reduction of CO2 to high-quality uniform AMS targets whose morphology we visualized using scanning electron microscope pictures. Key features of our optimized method were to reduce CO2 (from a sample of interest that provided 1 mg of C) using 100 ± 1.3 mg of Zn dust, 5 ± 0.4 mg of −400MSIP, and a reduction temperature of 500 °C for 3 h. The thermodynamics of our optimized method were more favorable for production of graphite-coated iron powders (GCIP) than those of previous methods. All AMS targets from our optimized method were of 100% GCIP, the graphitization yield exceeded 90%, and δ13C was −17.9 ± 0.3‰. The GCIP reliably produced strong 12C− currents and accurate and precise Fm values. The observed Fm value for oxalic acid II NIST SRM deviated from its accepted Fm value of 1.3407 by only 0.0003 ± 0.0027 (mean ± SE, n = 32), limit of detection of 14C was 0.04 amol, and limit of quantification was 0.07 amol, and a skilled analyst can prepare as many as 270 AMS targets per day. More information on the physical (hardness/color), morphological (SEMs), and structural (FT-IR, Raman, XRD spectra) characteristics of our AMS targets that determine accurate, precise, and high-hroughput AMS measurement are in the companion paper

Radiocarbon Dating of Copper-Preserved Organics

From the 14th International Radiocarbon Conference held in Tucson, AZ, May 20-24, 1991.The small but vital role of 14C dating in archaeometric research is clearly shown in the copper project reported herein. The 14C ages place a time perspective on the "Old Copper Culture Complex," substantiating early Libby dates that had been questioned. The respective roles of INAA, PGE and Pb isotope work are briefly summarized. A long tradition of heat treatment from Paleoindian stone to Archaic copper is suggested.This material was digitized as part of a cooperative project between Radiocarbon and the University of Arizona Libraries.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

Radiopurity of the Borexino Scintillator

This report summarizes the results of a research program on the radiopurity of the Borexino scintillator. Three aspects were focused: 1) ultratrace determination of impurities in commercial organic scintillator solvents; 2) recontamination rates and 3) methods for repurification. This work has covered several solvents and a wide range of impurities. Rates for recontamination of several materials have been measured and impurity patterns of contamination at different stages from manufacture to measurement can be qualitatively modeled. The main radiopurity problem for Borexino will be repurification of continuing contamination from the vessel itself. The operating background in Borexino is most likely to be determined by leached 210-Pb and 40-K, rather than the U/Th/daughters group, traditionally considered the major background generators

Radiocarbon Dating with Tandem Electrostatic Accelerators

From the 10th International Radiocarbon Conference held in Bern, Switzerland and Heidelberg, Germany, August 19-26, 1979.An MP tandem Van de Graaff accelerator at the University of Rochester has been employed since May 1977 to detect 14C in various terrestrial samples. The carbon sample sizes required are lmg or less. Dating accuracies based on reproducibility now approach (+/- 80 years). Measurements have been made on 1850 wood, Australian sucrose, a carbon sample from Mt Shasta, a baby woolly mammoth, and an Egyptian bull mummy wrapping.This material was digitized as part of a cooperative project between Radiocarbon and the University of Arizona Libraries.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

Evidence from the northwestern Venezuelan Andes for extraterrestrial impact: The black mat enigma

International audienceDespite the high success of the NICA-Donnan (N-D) model to describe the interaction of protons and metal ions with natural organic matter, the large number of fit parameters is a major hindrance to its capacity to provide unique numerical solutions. This well-known difficulty is reflected in the unusually low value of the generic proton binding constant for carboxylic-type groups of fulvic acid (pKH1 = 2.34), and to some extent of humic acid (2.93), and by the considerable covariance of the other generic N-D parameters. In some studies, the number of parameters obtained by regression is reduced by estimating some values independently with other techniques. Alternatively, the applicability of the model can be improved by devising a rigorous simulation procedure, which constrains the model-fit to converge toward chemically and physically realistic values. A procedure based on three successive iterations is proposed, and the solution is shown to be stable and invariant with the initial set of parameter values. The new generic parameters, in particular pKH1(FA) = 3.54 and pKH1(HA) = 3.87, derived from the same data set as the previous generic parameters, are in better agreement with literature data

Out of the Cave and into the Light: Perspectives and Challenges of Radiocarbon Dating an Open-Air Aurignacian Site (Régismont-le-Haut, Mediterranean France)

International audienceThis article presents the methods and results regarding the radiocarbon (AMS) dating of the site of Régismont-le-Haut. This site is one of the very few well-preserved Aurignacian open-air sites in southern France. It is also one of the only Aurignacian sites in France and Europe, more generally, to have conserved evident features, including many in situ fire-related structures. We selected charcoal and bone from all the major occupation sectors excavated so far, as well as from others which were important for understanding site formation. Considering difficulties faced when comparing the lithic industry of a site located in a poorly documented area with those belonging to the Aquitaine basin, where the "classical" definition of the Aurignacian was outlined, dating was conducted to accurately place the site within this technocomplex's internal chronology. In total, 19 charcoals (identified to Pinus sp. or gymnosperm) and 3 bones were submitted for AMS radiocarbon dating, each to one of three laboratories. We implemented a strict charcoal screening protocol for radiometric dating that required genus-identified individual charcoals that were well-associated with the fire-related structures. Despite this careful selection , most of the charcoals and all of the bones contained insufficient carbon for dating. Of the 19 charcoal dates attempted, 5 produced dates, from two loci. All fall in the span between the Middle Aurignacian and the Recent Aurignacian (between around 32,500 and 28,000 uncalibrated 14 C BP). An older subset of the dates (32.5-32 ka BP, ca. 37.5-35.5 ka cal BP) appears to be the most reliable. These results represent the first AMS dates ever performed on an Aurignacian open-air site in the Mediterranean area. The dates are compared to other recently dated southwestern France sites to establish which ones might be useful for future detailed archaeological comparisons. They are also instructive from a methodological point of view, in order to better appreciate the resolution of radiocarbon in this context. The focus of this article is on presenting the dating work, especially the protocol used in the selection of samples, the laboratory methods used for obtaining the dates and the challenges faced at this site. Among these, the divergence of dates between loci contrasted with geomorphological and archaeological evidence, with the latter two strongly pointing to one living floor, and either a single occupation or a few very close in time. This forced a reassessment of the chronological dating evidence. This article serves to show the importance of multi-prong approaches to archaeological dating, comparing and contrasting both contextual evidence and actual dates