Doubting radiocarbon dating from in-slag charcoal

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2010

Radiocarbon is a cosmogenic radioisotope equally distributed throughout the troposphere and biosphere. This fact enables its most common application-radiocarbon dating. Natural equilibrium of radiocarbon has been disturbed by diverse anthropogenic activities during the last $ 150 years, enabling also the use of 14 C in various environmental applications. Here we present three types of studies by using 14 C that were performed in the Zagreb Radiocarbon Laboratory. 14 C in atmospheric CO 2 has been monitored at several sites with various anthropogenic influences and the difference between the clean-air sites, the industrial city and the vicinity of a nuclear power plant has been established. 14 C has been applied in geochronology of karst areas, especially in dating of tufa, speleothems and lake sediments, as well as in studies of geochemical carbon cycle. 14 C has been used in various archaeological studies, among which the dating of the early Neolithic settlements in Croatia is presented. In these studies 14 C was measured by radiometric techniques, i.e., by gas proportional counting and more recently by liquid scintillation counting (LSC). Two sample preparation techniques for LSC measurement were used: benzene synthesis for archaeological dating and other applications that require better precision, and direct absorption of CO 2 for monitoring purposes. The presented results show that various studies by using 14 C can be successfully performed by the LSC technique, providing a large enough sample (41 g of carbon).

Radiocarbon, 1969

Dates listed below are based on measurements made up to May 1968, and cover a period during which the technique of gas proportional counting using CO2 was gradually replaced by liquid scintillation counting using benzene. The gas counting measurements were carried out by the method and techniques previously described (Barker and Mackey, 1968) the only modifications being the replacement of some old electronic units by more stable solid-state equipment; proportional counting results are indicated in the text by (P) at the end of the relevant sample descriptions. Liquid scintillation counting, which is now the preferred method in this laboratory, is carried out using a Packard Tri-Carb liquid scintillation spectrometer model 3315/AES fitted with selected low-noise quartz-faced photomultipliers. Normally 3 ml of benzene is prepared from each sample. This is dissolved in 12 ml of scintillation grade toluene containing 5 gm/liter of scintillator (PPO) and the solution is measured in a standard low-potassium glass vial at a temperature of 0°C. Photomultiplier E.H.T., amplifier, and channel width settings are optimized for C14, and measurements are carried out at ca. 65% efficiency of detection for C14 to eliminate interference from any tritium which may be present in the benzene. Under these circumstances the background is approx. 8.6 cpm and the modern (95% A0X) is approx. 24.0 cpm. Samples are counted in groups of 3 to 5 together with background and modern reference samples and are measured for at least one week, the instrument being set to cycle at 100 min intervals. In this period, the counts accumulated are such that the background is always measured to a statistical accuracy of better than 1% and most other samples to a higher accuracy than this. Background and modern counts used in the calculation of each result are only those relevant to the period of measurement of that particular sample. Statistical analysis of groups of replicate measurements made under these conditions over a very long period of time has demonstrated the excellent long-term stability of the equipment and indicates that the technique is quite capable of achieving results of very high statistical accuracy when required. SAMPLE DESCRIPTIONS ARCHAEOLOGIC SAMPLES A. Crete Knossos series Five samples from Neolithic settlement of Knossos, Crete (35° 31' N Lat, 25 ° 20' E Long), from sounding below central court of Minoan Palace (Evans, 1964a,b). Coll. 1960 and subm. by J. D. Evans, Inst. of Archaeol., Univ. of London, for comparison with unexpectedly early dates previously obtained for Knossos Neolithic, BM-124, 8050 ± 180 and BM-126, 7000 + 180 (Radiocarbon, 1963, v. 5, p. 104). 7570 ± 150 BM-272. Knossos 2 5620 B.C. Sample 2, ref. Area AC, Level 24. Charcoal from Occupation layer assoc. with 1st brick houses and immediately overlying earliest camp occupation above bedrock (Stratum IX, Evans, 1964b). Expected age early 6th millennium B.C. based on BM-124 and BM-126. (P) 6210 ± 150 BM-273. Knossos 3 4260 B.C. Sample 3, ref. Area AC, Level 17. Charcoal from habitation deposit in Stratum VI (Evans, 1964b). Expected age late 6th millennium B.C. based on BM-124 and BM-126. (P) 6140 ± 150 BM-274. Knossos 4 4190 B.C. Sample 4, ref. Area A, Level 15. Charcoal from habitation level in Stratum V (Evans, 1964b). Expected age end of 6th millennium B.C. based on BM-124 and BM-126. (P)

Four charcoal samples from loess key sites in Austria, Moravia, and western Ukraine were submitted to ABOx (acid-base oxidation) pretreatment to compare results with the classical ABA (acid-base-acid) method. For this purpose, charcoal samples already dated in Groningen laboratory were selected from 3 archaeological sites: Molodova V in western Ukraine (subunit 10-1, ~32.6 ka BP), Willendorf II in Austria (unit C4, ~32.1 ka BP and unit C8, ~38.9 ka BP) and Vedrovice V in Moravia (unit 4, upper part of Bohunice soil, ~39.5 ka BP). Each selected charcoal sample has been homogenized and divided into 3 subsamples, which were submitted to ABA in Groningen and to ABA and ABOx pretreatments in Oxford. The results show that the ABOx dates are older than the ABA dates. Nevertheless, down to ~40 ka BP ABOx and Groningen ABA dates appear in good agreement within a time interval of ~1 millennium at 1. However, Groningen ABA pretreatment produces older dates than the Oxford ABA pretreatment. Both Oxford ABOx and Groningen ABA pretreatments provide sets of dates in good agreement with the chronological background of each selected site.

Geochronometria, 2000

In this work an age model for a peat core from the site near Żyglin, based on 14 C is presented. The investigated profile is marked with some possible evidence of early human activity in this region. The earliest metallurgy industry is expected to correspond with charcoal production and the recent increase of metal content in this profile. In this work the Quantulus 1220™ recently purchased was used for 14 C dating with liquid scintillation counting (LSC) technique. Therefore results of calibration, tests and verification with use of samples from inter-comparison programs (VIRI, FIRI) are also presented.

Radiocarbon, 1991

The results presented in this list were obtained from 1986 to 1989. Equipment, measurement and treatment of samples are as reported previously (Kanwiszer & Trzeciak 1984: 111). Age calculations are based on a contemporary value equal to 95% of the activity of NBS oxalic acid standard and on the conventional half-life for 14C of 5568 ± 30 years. Results are reported in years before 1950 (years BP). Errors quoted (± 1σ) include standard deviations of count rates for the unknown…

Radiocarbon 55(3-4), 641-7., 2013

Four charcoal samples from loess key sites in Austria, Moravia, and western Ukraine were submitted to ABOx (acid-base oxidation) pretreatment to compare results with the classical ABA (acid-base-acid) method. For this purpose, charcoal samples already dated in Groningen laboratory were selected from 3 archaeological sites: Molodova V in western Ukraine (subunit 10-1, ~32.6 ka BP), Willendorf II in Austria (unit C4, ~32.1 ka BP and unit C8, ~38.9 ka BP) and Vedrovice V in Moravia (unit 4, upper part of Bohunice soil, ~39.5 ka BP). Each selected charcoal sample has been homogenized and divided into 3 subsamples, which were submitted to ABA in Groningen and to ABA and ABOx pretreatments in Oxford. The results show that the ABOx dates are older than the ABA dates. Nevertheless, down to ~40 ka BP ABOx and Groningen ABA dates appear in good agreement within a time interval of ~1 millennium at 1. However, Groningen ABA pretreatment produces older dates than the Oxford ABA pretreatment. Both Oxford ABOx and Groningen ABA pretreatments provide sets of dates in good agreement with the chronological background of each selected site.

Radiocarbon, 1969

The following list covers some old measurements not included in previous lists and most of the samples measured at the Uppsala C14laboratory since the last list (Radiocarbon, 1967, v. 9, p. 454-470); samples utilized for determining the increase of the C14/C12ratio clue to explosion of nuclear devices are omitted

In this paper the precision and accuracy of radiocarbon dating in Gliwice Radiocarbon Laboratory on the background of intercomparision programs is discussed. Here are briefly presented results of individual comparisons between laboratories from eight countries and three international intercomparison programmes: ISC Programme (1986), TIRI Programme (1994) and FIRI Programme (1999). Moreover the short description of Gliwice Radiocarbon Laboratory is presented. The main stress is laid on the description of FIRI Programme -types of samples included in Programme and methods of calculation of consensus values, but first of all the participation of our Laboratory in the programme is presented: pretreatment procedures of samples, results obtained in Gliwice and statistical analysis of these results. The most important conclusion, which may be drawn from this paper, is that Gliwice Radiocarbon Laboratory dating results are not biased by systematic error.

RADIOCARBON, Vol 51, Nr 2, 2009

The subject of this article is the radiocarbon dating on bones in the western European Neolithic. By gathering 14C dates for 2 examples, one chosen in the middle Neolithic of the Rhine region and the other in the end of the early Neolithic in the same region and in the Paris Basin, a significant gap appears between the sum probabilities of dates on charcoals and the ones obtained with bones. A comparison between these results with the few available dendrochronological dates shows that dates on bones seem too young, while the sequence based on charcoals fits. The existence of too-young 14C dates of bones is not new: this phenomenon was already indicated in previous studies. Most explanations agree that there was a source of contamination, during the sample’s burial or its treatment in laboratory. These examples illustrate that consequences can be heavy on a chronology built, partly or entirely, on 14C dates of bones.

Radiocarbon, 2013

Four charcoal samples from loess key sites in Austria, Moravia, and western Ukraine were submitted to ABOx (acid-base oxidation) pretreatment to compare results with the classical ABA (acid-base-acid) method. For this purpose, charcoal samples already dated in Groningen laboratory were selected from 3 archaeological sites: Molodova V in western Ukraine (subunit 10-1, ~32.6 ka BP), Willendorf II in Austria (unit C4, ~32.1 ka BP and unit C8, ~38.9 ka BP) and Vedrovice V in Moravia (unit 4, upper part of Bohunice soil, ~39.5 ka BP). Each selected charcoal sample has been homogenized and divided into 3 subsamples, which were submitted to ABA in Groningen and to ABA and ABOx pretreatments in Oxford. The results show that the ABOx dates are older than the ABA dates. Nevertheless, down to ~40 ka BP ABOx and Groningen ABA dates appear in good agreement within a time interval of ~1 millennium at 1. However, Groningen ABA pretreatment produces older dates than the Oxford ABA pretreatment. Both Oxford ABOx and Groningen ABA pretreatments provide sets of dates in good agreement with the chronological background of each selected site.

Isotopes in Environmental and Health Studies, 2002

In the Gliwice Radiocarbon Laboratory, a system for preparation of samples for AMS dating has been built. At first it was used to produce graphite targets from plant macrofossils and sediments. In this study we extended its capabilities with the preparation of bones. We dealt with 3 methods; the first was the classical Longin method of collagen extraction, the second one included additional treatment of powdered bone in alkali solution, while in the third one carboxyl carbon was separated from amino acids obtained after hydrolysis of protein. The suitability of the methods was tested on 2 bone samples. Most of our samples gave ages >40 kyr BP, suggesting good performance of the adapted methods, except for one sample prepared with simple Longin method. For routine preparation of bones we chose the Longin method with additional alkali treatment.

Naturwissenschaften, 1991

Radiocarbon, 1971

Dates listed below are based on measurements made from June 1968 to May 1970 by the liquid scintillation technique using benzene. In general, the experimental procedure is as described previously (Barker, Burleigh, and Meeks, 1969a) with a few changes in detail. Data are now processed by computer using a comprehensive Algol program written by Andrew Barker, King's College, Univ. of London. There is no need to standardize on any particular sample weight and, as the benzene synthesizer can also deal with samples in the range up to the equivalent of 9 gm of carbon in a single synthesis, the amount of sample available is now less critical. However, for older material, a minimum of 1 gm of carbon is required. Another factor contributing to efficiency of operation is the "bomb" technique for sample combustion (Barker, Burleigh, and Meeks, 1969b), also mentioned in the previous date list. Finally, during 1969, an MS20 double collection mass spectrometer was acquired and all dates (but not all those in this list) are now corrected for isotopic fractionation. Samples were pretreated for removal of contaminants, with dilute hydrochloric acid and, where appropriate, with dilute alkali also. Bone and antler samples were demineralized in low vacuum with 0.75 N hydrochloric acid at ambient temperature, leaving only the protein fractiori (collagen) which was washed and dried before combustion. Dates were calculated using the Libby half-life for C14 of 5568 years. Descripdons, comments, and references to publications are based on information supplied by the persons who contributed the samples. ACKNOWLEDGMENT Thanks are due to Miss G. I. Hassall, National Physical Laboratory, for isotopic fractionation measurements made in connection with the investigation of C14 age discrepancies using well-dated Egyptian materials.

Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2005

Radiocarbon dating of iron samples is, in spite of partially promising attempts in the last decades, still no established standard procedure. One of the main problems in preparing iron is the low carbon content which makes the needed sample size too big for some sample combustion systems. Also the metallic character of the samples complicates sample combustion or oxidation. This required in most cases an own preparation line only for iron samples. To avoid this problem two different ways are being followed at the Erlangen AMS-facility. One is direct sputtering of the unprocessed iron sample in the ion source. The other is the complete extraction of carbon from the iron sample and dating of the carbonaceous residue. First results from archaeological iron samples of known age, prepared and dated by these two methods, are presented and discussed.