Low level gas multicounter for 14C dating of small samples

A compact gas multicounter has been constructed and is undergoing tests. Up to 14 methane samples can be counted simultaneously in an array of 10 ml (at NTP) copper counters at a pressure of 1–8 bar. The gas filling, application of high voltage and decay energy monitoring are microprocessor controlled. Multichannel analyses (256 ch. sample and cosmic detector energy data), sample identity, counting time and critical validity parameters are stored on disc. Numerical discrimination and manipulations of counting parameters can be performed without destroying the original data set. Statistical quality control is based on chi-square and Poisson distribution of countrates around their mean in user defined energy regions as well as “ time of arrival” (TA) of pulses mode. TA analysis offers the user an early means of recognition of some types of system malfunction that otherwise might remain undetected for long periods of time. Pulse shape analysis is used to discriminate sample beta from environmental radiation pulses resulting in a low background with compact and relatively inexpensive shielding.     

Archaeological and geological interest in applying 14C AMS to small samples

One aspect of the accelerator mass spectrometry technique is that samples can be dated which are essentially smaller than required for conventional ¹⁴C dating. This two orders of magnitude expansion offers applications of ¹⁴C which are new and in some fields of great importance. This paper attempts to list and group the various types of sample materials, with special emphasis on their role in archaeology and geology.     

Properties of milligram size samples prepared for AMS 14C dating at ETH

We have investigated the ion beam characteristics (intensities, yields, duration and stability) of a variety of targets prepared for radiocarbon dating by AMS. The target preparation techniques include: organic matter pyrolysis products mixed with silver, high pressure temperature ‘graphites’, CO reduction by cracking, magnesium reduction of CO₂ and direct dating of extractives. Values for minimum sample amounts, sample preparation times, contamination as judged by background and precision of determination are given and the overall performance is evaluated.     

Direct measurements of small 14C samples after oxidation in quartz tubes

Small ¹⁴C samples gain importance in environmental research and for dating purposes. However, throughput of such samples is limited by the preparation of graphite targets for accelerator mass spectrometry (AMS) measurements. In our approach, oxidation of samples with copper oxide in quartz tubes was applied to form CO₂ which was measured directly with the gas ion source of the small AMS facility MICADAS. The presented method was designed to meet the requirements for fast and easy handling of small samples (<100 μg carbon). As combustion byproducts are likely to interfere with ionisation processes in the gas ion source, we additionally investigated the effects of several gases on C^? currents.     

Correlation of the paleoclimatic record in lacustrine sediment sequences: 14C dating by AMS

We have determined ¹⁴C ages by accelerator mass spectrometry (AMS) for small amounts (5–20 mg) of terrestrially derived organic remains taken from a sediment core drilled from Lake Zürich, Switzerland. The continuous core relates in part to Late-Glacial and Holocene glacial-to-lacustrine sediments.Samples were selected after careful consideration of sedimentological criteria, and prepared for AMS using the high-pressure-temperature method of graphitization. Precise ages at seven levels in the sequence, combined with sedimentologic interpretation of the core, establish a new chronology for deglaciation and subsequent climatically induced events within the catchment. Evidence indicates a later disappearance of glacial ice from the Lake Zürich basin than previously reported.     

14C dating of the Early to Late Bronze Age stratigraphic sequence of Aegina Kolonna,Greece

Aegina Kolonna, located in the center of the Saronic Gulf in the Aegean Mediterranean (Greece), is one of the major archaeological sites of the Aegean Bronze Age with a continuous stratigraphic settlement sequence from the Late Neolithic to the Late Bronze Age. Due to its position next to the maritime cross roads between central mainland Greece, the northeast Peloponnese, the Cyclades and Crete, the island played an important role in the trade between these regions. In the course of new excavations, which focused on the exploration of the Early, Middle and Late Bronze Age at Kolonna, several short lived samples from different settlement phases have been ¹⁴C-dated with the AMS method at the VERA laboratory. Bayesian sequencing of the ¹⁴C data according to the stratigraphic position of the samples in the profile was performed to enable estimates of the transition time between the cultural phases. The Aegina Kolonna ¹⁴C sequence is one of the longest existing so far for the Aegean Bronze Age, and therefore of major importance for the absolute Bronze Age chronology in this region. Preliminary results indicate that the Middle Helladic period seems to have started earlier and lasted longer than traditionally assumed. Further, at the present stage of our investigation we can give also a very tentative time frame for the Santorini volcanic eruption which seems to be in agreement with the science derived VDL date.     

The hardwater effect in AMS 14C dating of food crusts on pottery

The pottery investigated in this study comes from late mesolithic inland sites next to rivers in Northern Germany. The first AMS ¹⁴C datings of food crusts from these sites showed surprisingly high ages, which could be caused by the hardwater effect.Modern samples from the rivers have ages of several hundred ¹⁴C years, and a modern food crust prepared from fish with a certain reservoir age shows the same age as the fish. Surprisingly, there was a large age difference between water samples and fish/mollusc shell from the same river. Associated archaeological samples of terrestrial and fluvial origin show age differences of several hundred and up to 3000 years. These high age differences are only to a limited extent transferred to the archaeological food crusts.     

ZSS单板机在~(14)C年代测量中的应用

一、14C年代测定单板机的功能1.数据处理 1)被测样品的在线数据处理 14C年代测量时间较长,一般一个样品要测够1000分钟,每10分钟为一段,测量到预置的时间后,单板机就用“3σ”作判据对各段计数进行统计检验,对偏离值超过“3σ”的数据可剔除掉,若要求测量时间一致,还可再补充新的测量值,经过剔除和补充后,将得到“σ1”值,再用“3σ1”作判据,重新进行统计检验,直至全部偏离值没有超过“3σn”为止。仪器及电网负载工作状态正常时,偏离值超过“3σn”的机率只有3‰,所以一般不需要剔除和补充。当测量结束时,打印机打出样品的平均计数率、标准误差、试验误     

A new graphite preparation line for AMS 14C dating in the Zagreb Radiocarbon Laboratory

The new line for preparation of graphite samples for ¹⁴C dating by AMS has been constructed in the Zagreb Radiocarbon Laboratory. The performance of the rig and sample preparation procedure has been validated by preparing graphites from various reference materials of known ¹⁴C activity. The yield of the graphitization was good and the measured fraction of modern carbon (F_m) values have not significantly deviated from the expected ones. Detailed analysis of measured F_m values indicates a slight bias to more positive values and should be carefully investigated.     

Long term stability of iron for more than 1500 years indicated by archaeological samples from the Yamato 6th tumulus

One of the candidate materials for overpack in the Japanese engineered barrier system for high-level radioactive waste (HLW) is iron and therefore its long-term stability for at least 1000 years is very important for safety analysis of the repository system. Therefore, several of the iron artifacts excavated from the Yamato 6th tumulus (ancient tomb) in Nara prefecture were analyzed using X-ray computed tomography (CT) to determine corrosion depth. The samples analyzed, both of two large and 11 smaller iron artifacts are called ‘Tetsutei’. The thickness of each rust layer was measured from a cross-section image of the sample and the difference in material density between rust and iron was shown by the image density by the X-ray CT. In the case of pitting corrosion in the sample, the depth of the pits was measured directly and estimated as total corrosion depth with general corrosion layer. The corrosion depths are 0.5–2.1 mm. These data indicate conservative predictions for the extrapolations based on experimental studies. Such corrosion data from archaeological samples are useful in analogue studies of high-level radioactive waste disposal as evidence of long-term stability of a waste container.     

Radiocarbon dating and wiggle matching of wooden poles forming circular structures in the 1st Millennium BC at the Mawaki archaeological site,central Japan

Wooden circular structures, presumed archaeologically as a structure related with ritual of ancient people in the Final Jomon period, are specific to archaeological sites excavated mainly in the coastal region around Noto peninsula, central Japan. So far, only few attempts have been made at chronological studies on these wooden structures. ¹⁴C dating has been attempted to wooden poles forming the structures, which had been excavated at the Mawaki archaeological site, Ishikawa prefecture, central Japan, to examine construction period of the structures. It was revealed that these structures were constructed in the Final Jomon period, most probably within 900–400 cal BC. In addition, we have tried wiggle matching of ¹⁴C ages for several annual rings separated from three and two poles that were constituting two circular structures, the oldest and the newest ones. ¹⁴C dates of annual rings measured with AMS were wiggle-matched to IntCal04 data sets by Bayesian statistics. The results indicated that the construction period of these wooden structures can be placed within ca. 820–680 cal BC, being narrowed by about 350 calendar years successfully.     

Accelerator mass spectrometry sample preparation: Methods for 14C in 50–1000 microgram samples

A joint project was undertaken by the National Bureau of Standards (NBS) Atmospheric Chemistry Group and University of Arizona (UoA) Tandem Accelerator Mass Spectrometry Group to develop and evaluate accelerator ¹⁴C measurements of 50–1000 μg carbon samples at a modest accuracy of 5–10%. FeC alloy targets prepared from standards and samples averaged 1.6 μA ¹²C^? current. ¹⁴C measurements yielded 5% precision and accuracy, limited by a blank equivalent to 11% modern carbon for targets containing ～ 100 μg carbon. The contamination level was estimated to be ～ 15 μg contemporary carbon (current atmospheric ¹⁴C). These results demonstrated that the FeC target is quite suitable for atmospheric and environmental studies that require measuring fossil/biogenic carbon in microgram samples.     

A portable PIXE system for the in situ characterisation of black and red pigments in neolithic, copper age and bronze age pottery

The results of the determination of the chromophoric elements in black and red pigments in ancient neolithic, copper age and bronze age pottery are presented. The measurements were carried out by using a recently developed portable PIXE system and were performed at the Archaeological Museum of Licata (Sicily). The results confirm the presence of Manganese in black pigments of Castelluccio style pottery and indicate, for the first time, a strong presence of manganese in copper age pottery of the Serraferlicchio style, and in neolithic pottery of the Serra d'Alto style.     

秦山核电基地环境生物样品中14C监测方法探讨

介绍了氧弹法在秦山地区环境生物样品中¹⁴C监测中的应用情况,对氧弹法的特点进行了分析,并对秦山核电基地历年来环境生物样品中¹⁴C监测的结果进行了分析。希望本方法能对生物样品中¹⁴C监测方法的新国标的制定提供参考。     

南海北部深海沉积物热释光测量研究

本文用热释光断代研究了深海沉积物的年龄,测得南海北部陆坡维玛一、五、六井中的沉积物年龄分别36、100和128千年。     

The AMS 14C dating of Iron Age rice chaff ceramic temper from Ban Non Wat,Thailand: First results and its interpretation

Pottery tempered with rice chaff from the early Iron Age cemetery of Ban Non Wat site, northeast Thailand, has been subjected to direct AMS ¹⁴C dating, using low temperature combustion with oxygen as originally developed by authors. The carbon yield (0.2–0.5%) testifies the suitability of this pottery for dating. However, not all the results are in agreement with expected archaeological ages and other ¹⁴C dates from the studied site and neighboring site of Noen U-Loke. This calls for a thorough analysis and interpretation of pottery temper dates from the region.     

试论~(14)C测量中的闪烁溶液

本文主要分析~(14)C液体闪烁测量中常遇到的闪烁溶剂与有机闪烁体(发光物质),并将我们测试情况作一介绍与论证,为从事这方面工作的同志,正确选择使用闪烁溶液创造条件。为了叙述方便有必要将闪烁测量过程作一简介,其过程如图1所示。