GLIWICE RADIOCARBON LABORATORY

Some solved important problems

Improved precision radiocarbon dating and natural ¹⁴C variations around 10,000 cal BP.

In this study, ¹⁴C dates from the tree-rings of oak from Lublinek were obtained. This series covered the 300 year long period around 10,000 cal BP. For the purpose of this study, the precision of ¹⁴C dating was improved significantly, reaching ca. 30 years for the samples 10000 year old. It was shown that the whole time span studied was the period of the constant radiocarbon age of ca. 9000 ¹⁴C BP. This reflected the strong decline of ¹⁴C concentration in the atmosphere at that time.

Calibration of radiocarbon time scale in the Late Glacial and early Holocene.

The series of terrestrial macrofossils has been collected from the sediments of Lake Gościąż, and dated by the AMS (accelerator mass spectrometry) method. These dates enabled absolute dating of the floating varve chronology. Using the specially developed improved algorithm of wiggle-matching, the floating chronology was dated with the accuracy of 40 years. The beginning of Holocene was thus dated to 11,510±40 cal BP. This study also showed that the beginning of the Holocene occurred in the middle of plateau of radiocarbon age 10,000 ¹⁴C BP, and demonstrated large increase of ¹⁴C concentration in the atmosphere at the onset of the Younger Dryas cold period which was explained by a drastic weakening of vertical water circulation in the North Atlantic during the first 300 years of YD.

Carbon isotope composition and ¹⁴C apparent age of freshwater tufaceous sediments.

Synthetic approach to ¹⁴C dating of calcareous tufa, based on statistical analysis of correlation between lithologic type of tufaceous sediment, carbon isotope composition and apparent age was presented. It was found that the relation between the apparent age and δ¹³C value of tufa depends on lithologic type of tufa. Phenomenological equations describing this dependence and applications to estimation true ages of tufa were given.

Variations of isotopic composition of carbon in the karst environment from Southern Poland. Present and past.

A comprehensive study of carbon isotopes in several karst springs and their environs in a contemporary karst environment in the region of Cracow Wieluń - Upland and Western Tatra Mts, Southern Poland, was carried out. Samples of water, plants and carbonate deposited on aquatic plants, were collected and ¹³C values and ¹⁴C concentrations obtained. Also investigated were a group of the youngest calcium carbonates from caves where deposition is still being observed or ceased no more than a few hundred years ago. The determination of a ¹⁴C dilution factor in these carbonates provides a possibility of determining the "true" radiocarbon ages of old speleothems from caves in the area under investigation and the use of old speleothems as suitable material for extending the ¹⁴C calibration time scale; the "Absolute" age having been determined by U/Th or AAR dating methods. Radiocarbon dating of 89 speleothems from 41 caves were performed and 170 ¹⁴C dates obtained by 1994 for age distribution and palaeoclimatic interpretation.

Reliability of mollusc shell samples for radiocarbon dating.

The goal of this research was to find conditions under which mollusc shells give reliable radiocarbon dates. Terrestrial shells and marine ones appeared to be the most suitable for dating, since their apparent age is known quite well. A relatively simple method of thermal analysis to determine mineralogical composition of shells was tested. Experiments with recrystallisation of aragonite shells to calcite had shown no measurable effect of recrystallisation on ¹⁴C age. It had been shown, however, that outer parts of old shells may be contaminated by modern carbon. The ¹⁴C datings of series of shells from Svalbard enabled reconstruction of the rate of isostatic uplift of that region during the deglaciation.

¹⁴C, TL AND U/Th dating of the Vistulian lake sediments from Jaroszów site, SW Poland.

The ¹⁴C, TL and U/Th dating was made on samples taken from quaternary sediments profile of 50 m thickness, placed at the clay mining area in Jaroszów site, SW Poland. The stratigraphy order of sediments was as follows: fluvial gravels at the bottom of the profile, followed by gravels and laminated muds, massive muds, sands and gravels, organic sediments with layers of carbonates and gravels. At the upper part of sediments there are layers of muds, fluvial gravels followed by marl and peat. Organic sediments and marl were dated using ¹⁴C method (44 dates), carbonates-U/Th (10 dates), and fluvials-TL (12 dates). Obtained this way chronology of sedimentary processes together with their chemical, palinological, malacological, paleomagnetic and stable isotope analysis give the opportunity to make temporary reconstruction of environmental changes in the Vistulian period, i.e. in the range from ca. 100 to 13 ka BP. Lacustrine sedimentation of Jaroszów sediments was interrupted by periods of fluvial erosion, with temporal rhythm of these processes determined by climatic changes: ca. 100/80-60 ka BP-period of "polar desert", ca. 60-40 ka BP-warm phase, ca. 40-35 a BP-cold period of bush tundra and boreal forests, ca. 35-25 ka BP-warm phase, ca. 25-20 ka BP-grass tundra and ca. 20-13 ka BP-cool phase with bush tundra.

Radiocarbon dating and dendrochronology of Neolithic and Lusatian Culture settlements from Central Poland.

Complex interdisciplinary analyses of material collected in systematical excavations on Site 1 in Żuławka Mała and Biskupin, Central Poland, permitted to distinguish several phases of occupation from Neolithic and Bronze periods. The relationship between radiocarbon and dendrochronological analysis and archeological dating have been done for Żuławka Mała site. Limits of particular occupation phases (5130-1410 BC, 4530-4420 BC, 3890-3570 BC, 2950-2570 BC, 2190-2040 BC, 1560-1410 BC, 1200-1410 BC) have been established as results of cumulative probability distribution of calendar ages of 37 radiocarbon dates. Dendrological analysis of 70 samples of oak wood from uncovered construction enabled to establish 4 floating chronologies. The fortified settlement of the Lusatian Culture (Bronze Age) in Biskupin has been discovered in 1934. Radiocarbon studies have been started in 1981 and were continued since 1991 with participation of Gliwice and Gif-sur-Yvette radiocarbon laboratories. The results of conventional radiocarbon dating of series of wood and charcoal samples collected from archaeological trenches show some scatter and locate the Biskupin settlement between 850 and 400 cal BC. Dendrochronological studies gave the date of 747 BC for the building of the older settlement. This date is seriously supported by wiggle matching technique, which as applied to series of C-14 dates of oak chronology spanning ca. 160 years, leads to the estimate of 730 ± 30 cal BC.

¹⁴C absolute chronology of the Pyramid III and the dynastic model at Pachacamac, Peru.

Pachacamac, covering an area of about 600 ha near the Pacific shore, is one of the largest and most important archaeological sites in Peru. Most of the monumental adobe-made buildings of the later pre-Inka period (or Late Intermediate Period, ca. Xth-XVth c. AD) are so-called pyramids with ramps, whose role has been interpreted in different ways, following the authors. Precize datation of the pyramids appears as a crucial step in the definition of the functionning of the whole site of Pachacamac in pre-Inka times. More absolute dates are available from another pyramid with ramps, which allow us to make comparisons and propose a new model of interpretation for the site of Pachacamac during the Late Intermediate Period.

¹⁴C and dendrochronological dating of the logboats from Poland.

The earliest dating of samples taken from logboats, that have been found in the area of Poland, were made in Gliwice Radiocarbon Laboratory in the late 70's and early 80's. The results of ¹⁴C dating (51 dates) include all published by then and not published, obtained during last several years' results. In the distribution of calibrated dates we find lack of samples of age between ca. 800 BC and ca. 300 AD. This result is surprising and detached from the results observed for Central Europe. The remained ranges of age, with high frequency of dates, are in good coincidence with similar periods obtained for Central Europe. Tree-ring analyses were carried out on samples of 18 pine logboats. Tree-ring dating of oak logboats was carried out on 58 growth sequences, dated against standard chronologies defined for the area of Poland. The results of radiocarbon dating and tree-ring analyses give consistency chronologies.

Changes of ¹⁴C concentration in modern trees from Upper Silesia region, Poland.

Radiocarbon concentration measurements in tree rings from Upper Silesia indicate significantly lower ¹⁴C concentration comparing to that occurring in "clean air" areas. This phenomenon is known as the Suess effect (Suees 1955) and is caused by contamination with inactive carbon originating from fossil fuels combustion. This effect is observed in large urban and industrial areas. Samples for the measurements presented in the paper were collected in some of the biggest cities in Upper Silesia like Gliwice, Ruda Śląska and Chorzów. The samples were annual tree rings (Populus nigra, Pinus silvestris) covering years from 1965 to 1992 and the atmospheric CO₂ collected weekly from December 1994 to December 1995.

Computer program for calibration of radiocarbon dates.

A conversion of radiocarbon dates into real calendar date was one of the most important problems of radiocarbon dating. In 1986 the Gliwice Radiocarbon Laboratory prepared the theoretical background for probabilistic calibration of ¹⁴C dates. It consist in transforming the initial Gaussian probability distribution of ¹⁴C date into an appropriate probability distribution of calendar time scale using the Baeys theorem. On the base of this theoretical background a computer program has been developed.

Development of computer radiocarbon databases.

The need for computer-based database systems for management and storage of radiocarbon dates and associated information was recognised and discussed in the eighties. The research project, the so-called Gliwice Radiocarbon DataBank (GdRDB), was started in 1986. Presently GdRDB contains about 2500 radiocarbon dates out of more than 7000 dates obtained in the Gliwice Laboratory and is increasing continuously.

ANDY database.

Parallel to the GdRDB project the second research project was initiated in 1989 in collaboration with the Andean Archaeological Mission of the Warsaw University. The main aim of this project was to establish database system containing information on all available radiocarbon dates of archaeological interest from the Central Andean region (Peru, Bolivia and Ecuador). This project was finished in 1994. The database was created using the dBASE IV software package.

Preparation of graphite targets for AMS ¹⁴C measurements.

Accelerator Mass Spectrometry technique is used for radiocarbon dating of very small samples, containing only milligrams of carbon. Radiocarbon concentration is measured in graphite target, prepared from CO₂ obtained after combustion or decomposition of sample. A complete system consists of equipment for sample preparation, combustion, CO₂ purification and graphitisation, and for production of accelerator target. The system has been applied for preparation of different types of samples, such as organic macrofossils, peat, charcoal, bones, pollen, carbonates and shells. The measurements of ¹⁴C concentration in prepared targets are performed in accelerator laboratory in Kiel, Germany and Poznań, Poland.

Liquid scintillation beta spectrometry for ¹⁴C and ³H measurements.

The operation of a liquid scintillation spectrometry system consisting of the Quantulus 1220 spectrometer and two vacuum rigs for benzene production started in 1994. The purchase of the equipment was supported by the IAEA Technical Co-operation Programme Project POL/8/-12. The work on the calibration of the instrument for the purpose of radiocarbon dating in three different counting geometries was undertaken. Throughout the process of calibration, comparisons were made with the slightly different procedures and parameters established for the low-level liquid scintillation counting of C-14 at the NERC Radiocarbon Laboratory in Scotland.

A method of continuous examination of counting efficiency during measurements of natural radiocarbon by CO₂ filled proportional counter.

The method is based on the recording the number N of muon coincidence counts in the two sections of GM guard counters in addition to the commonly used number L of coincidence counts in the proportional counter and the guard counters taken as a whole. It was shown that the ratio C = L/N depends only on the proportional counter performance and resembles its overall counting efficiency.

Measurements of the attachment of thermal electrons to oxygen molecules in the proportional counter with mixture CO₂ + O₂.

A three body coefficient of the electron attachment in collisions with oxygen and carbon dioxide molecules was determined. The results of the work had practical meaning in the application of the carbon dioxide proportional counters in radiocarbon measurements.

Counting statistics in low level radioactivity measurements with fluctuating counting efficiency.

A divergence between the probability distribution of the number of nuclear disintegrations and the number of observed counts, caused by counting efficiency fluctuation, was discussed. The negative binomial distribution was proposed to describe the probability distribution of the number of counts, instead of Poisson distribution, which is assumed to hold true for the number of nuclear disintegration only. Some consequences of counting efficiency fluctuation are investigated and corresponding formulae are derived: for detection limit as function of partial measurements and the relative amplitude of counting efficiency fluctuation, and for optimum allocation of measurement time between sample and background.

A needle gas counter for measurements of low beta radioactivity of solid emitters.

A double needle gas counter arrangement for measurements of low beta radioactivity of solid emitters was constructed. As a main counter, a gas needle counter, working in deeply reduced proportionality conditions, was used. The counter characteristics and experimental as well as theoretical results of the gas amplification analysis were given. The detection efficiency of these counters is equal to 100% in the case of samples of 10 mm diameter. The background is about 0.04 cpm.

Non-self-maintained electric discharge in air in cylindrical chambers.

Ionisation currents in atmospheric air at various gas pressures have been measured between the saturation current regime and the region approaching sparking voltage. A model was developed in which the theory of ionisation avalanches in proportional counters is extended by including negative ions of oxygen molecules. Results obtained indicate possibilities for using similar chambers for measuring some gas admixtures in air.

A Data Acquisition System with pulse-shape discrimination for proportional counters.

Since 1994 new data acquisition system with pulse-rise background reduction has been developed in the Gliwice Radiocarbon Laboratory. The system uses microprocessor-controlled pulse and coincidence analyser, based on a single-chip microcomputer 8051, for acquisition of data from proportional counters. Collected information allows distinguishing pulses produced by b-radiation of ¹⁴C from pulses generated by cosmic radiation and allows decreasing background count-rate to one third of its non-discriminated value. During long-term stability tests we found out large shifts of the rise-time spectra obtained in various measurement session, which caused significant changes in the count-rate. We ascertained, that the shifts are the consequence of various concentration of electronegative impurities. We worked up a method, which corrects the changes of count-rate by control of average rise-time of pulses generated by cosmic radiation and found out, that value of the average rise-time is very sensitive to differences of gas purity. Comparison with parameter used till now shows, that ARTL detects concentration of electronegative impurities better than the old one.

Standardisation of description of the gas amplification in proportional counters.

Since too many different formulae were used for first Townsend ionisation coefficient in description of the gas amplification in proportional counters, which had no physical basis, the Townsend formula was proposed as a standard.

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