We report on a review of 14C production and release from the nuclear industry in the United Kingdom (UK). Using earlier predictions (Bush, White and Smith 1984) it is estimated that a total of 1764 TBq of 14C would have been produced in UK graphite-moderated reactors up to the end of 1995, and 135 TBq of this total would have been released. Release rates, based on reported discharges, of 5.1 and 0.93 TBq GW(e)a-1 have been derived for Magnox reactors and Advanced Gas Cooled Reactors (AGRs), respectively. Using these new figures, cumulative discharges of 14C up to 1995 from reactors have been estimated at 531 TBq. The combination of these reactor discharges and the reported discharges from Sellafield (388 TBq) and Amersham (52 TBq) suggest a total cumulative release of 971 TBq of 14C up to the end of 1995.

14C is one of the radionuclides that are produced to different degrees by neutron-induced reactions in all types of nuclear reactors. Part of the 14C created is continuously released into the surrounding environment during normal operation as airborne effluents in various chemical forms (such as CO2, CO and hydrocarbons) through the ventilation system of the plant. Because of the biological importance of carbon and the long half-life of 14C, it is of interest to measure the releases and their incorporation into living material. We report here on the 14C activity concentrations in annual tree rings and the air around two Swedish nuclear power plants, as well as the background 14C activity levels from two reference sites in southern Sweden from 1973–1996. We used both accelerator mass spectrometry (AMS) and decay counting in the investigation.

Regular 14C sampling of discharged air began in 1988 at Paks Nuclear Power Plant (NPP), Hungary, and in 1991 at NPPs in Krsko, Slovenia and Bohunice, Slovakia. Monitoring of 14C discharges is carried out at all NPPs with similar differential samplers continuously collecting 14C in the form of 14CO2 and 14CnHm. The main results of airborne discharge monitoring are as follows: 14C activity concentration varied roughly within a factor of two around their mean values, 125 Bq m-3 and 90 Bq m-3 for Paks and for Krsko NPP, respectively. The pattern of discharge for Bohunice NPP is slightly different from that at the other two stations. At Bohunice, there has been a continuous increase in the discharge rate at power unit V1, starting with 70 Bq m-3 in 1991 and reaching a value of 190 Bq m-3 in 1995. The values for power unit V2 are 50 Bq m-3 and 82 Bq m-3. The average normalized yearly discharge rates are 0.887 (TBqGWe-1yr-1) for Paks, 0.815 (V1) and 0.500 (V2) for Bohunice, and 0.219 for Krsko. Most of the discharged 14C is in hydrocarbon form, 95% for Paks and Bohunice V2, but the CO2 fraction may reach 25% or 43% at Bohunice V1 and Krsko, respectively. At Bohunice V1, not only the discharge rate increased but the 14CO2 ratio to the total changed from 30% to 13%. The local radiological impact is estimated to be 1.5 μSv a-1 for Paks, 1.7 μSv a-1 for Bohunice, and 0.12 μSv a-1 for Krsko. The 14C excess in the environment has been measured at Paks NPP since 1989. Based on the monitoring data, the long-term average 14C excess from the Paks NPP was D14C=50% for hydrocarbons. Tree-ring analysis has shown a slight excess around Krsko NPP: D14C is equal to 199.9% for a tree at 1 km from the NPP compared with a “reference” one for which D14C was equal to 111.6% (in 1994).

Radiocarbon is an important constituent of the low level, liquid, radioactive effluent discharged from the Sellafield nuclear fuel reprocessing plant in northwest England, but despite the fact that it gives the highest collective dose commitment of all the nuclides in the waste, its behavior in the Irish Sea is poorly defined. There is therefore a clear requirement for an improved understanding of 14C behavior in the Irish Sea, to assist with dose evaluation modeling and definition of the mixing and accumulation characteristics of the sediment in this area. In this context, results are presented here for a temporal study of 14C activities in four geochemical fractions of seawater and in a sediment core from the vicinity of the Sellafield effluent outfall. Clear 14C enrichments in the dissolved inorganic carbon (DIC) and particulate organic carbon (POC) components of seawater were observed, with temporal trends in activity that were related to variations in the Sellafield discharge. Smaller, but nevertheless detectable, enrichments were also observed for particulate inorganic carbon (PIC) and dissolved organic carbon (DOC) in the seawater. The distribution of 137Cs and 241Am revealed that the sediment core could be classified into three zones in which the intensity of mixing decreased discontinuously with depth. Bulk carbonate 14C analyses of the core demonstrated the presence of glacial or pre-glacial carbonate in the system, but failed to show any evidence of contaminant 14C input or provide information on sediment accumulation processes. In contrast, analysis of bulk organic matter from the sediment provided clear evidence of the recent perturbation of a well mixed system by input of younger material, consistent with the recent input of contaminant 14C from Sellafield and possibly weapons testing fallout.

Statistical analysis is becoming much more widely used in conjunction with radiocarbon dating. In this paper I discuss the impact of Bayesian analysis (using computer programs such as OxCal) on archaeological research. In addition to simple analysis, the method has implications for the planning of dating projects and the assessment of the reliability of dates in their context.

A new formalism for describing chronological models is introduced here: the Chronological Query Language (CQL), an extension of the model definitions found in the program OxCal.

New methods of Bayesian analysis can be used to overcome some of the inherent biases in the uncertainty estimates of scientific dating methods. Most of these methods, including 14C, uranium series and thermoluminescence (TL), tend to favor some calendar dates over others. 14C calibration overcomes the problem where this is possible, but a Bayesian approach can be used more generally.

The conventional 14C time scale between 11,500 and 22,000 sidereal years has been calibrated by TIMS U/Th dates for corals. Only a few studies have been made for the time beyond this range. Obtaining samples suitable for numerical dating or estimating the reservoir correction of the 14C dates has been difficult, but we do not have these problems with TIMS U/Th dating of interstadial and interglacial lignite, because reservoir corrections are unnecessary.

Varved sediments of the tropical Cariaco Basin provide a new 14C calibration data set for the period of deglaciation (10,000 to 14,500 years before present: 10–14.5 cal ka bp). Independent evaluations of the Cariaco Basin calendar and 14C chronologies were based on the agreement of varve ages with the GISP2 ice core layer chronology for similar high-resolution paleoclimate records, in addition to 14C age agreement with terrestrial 14C dates, even during large climatic changes. These assessments indicate that the Cariaco Basin 14C reservoir age remained stable throughout the Younger Dryas and late Allerød climatic events and that the varve and 14C chronologies provide an accurate alternative to existing calibrations based on coral U/Th dates. The Cariaco Basin calibration generally agrees with coral-derived calibrations but is more continuous and resolves century-scale details of 14C change not seen in the coral records. 14C plateaus can be identified at 9.6, 11.4, and 11.7 14C ka bp, in addition to a large, sloping “plateau” during the Younger Dryas (∼10 to 11 14C ka bp). Accounting for features such as these is crucial to determining the relative timing and rates of change during abrupt global climate changes of the last deglaciation.

For a better understanding of pre-Holocene cultural history, archaeologists are in need of an absolute time scale that can be confirmed and duplicated by different dating methods. Proxy data available from archaeological sites do not, in themselves, allow much reflection on absolute age. Even when founded on supporting radiocarbon data, Paleolithic chronologies that are beyond the actual limits of 14C calibration still remain relative ones, and thus are often quite tentative. Lacking the possibility of calibration for the Paleolithic, archaeologists often attempt to correlate their data with different time scales from different archives that are thought to be absolute or calendric. The main result of this paper is that the GISP2 and U/Th chronologies duplicate each other over their entire range of data overlap, while other time scales (i.e., GRIP, most varve sites) differ significantly. The context-derived 14C calibration curve provides a large potential to correlate the various climate archives as recorded in ice cores and deep ocean drillings with terrestrial sequences.

A sequence of annually laminated sediments is a potential tool for calibrating the radiocarbon time scale beyond the range of the absolute tree-ring calibration (11 ka). We performed accelerator mass spectrometric (AMS) 14C measurements on >250 terrestrial macrofossil samples from a 40,000-yr varve sequence from Lake Suigetsu, Japan. The results yield the first calibration curve for the total range of the 14C dating method.

We present two new high-resolution sediment records from the southwestern Iceland and Norwegian Seas that were dated by numerous 14C ages up to 54 14C ka bp. Based on various lines of evidence, the local 14C reservoir effect was restricted to 400–1600 yr. The planktic stable isotope records reveal several meltwater spikes that were sampled with an average time resolution of 50 yr in PS2644 and 130 yr in core 23071 during isotope stage 3. Most of the δ18O spikes correlate peak-by-peak to the stadials and cold rebounds of the Dansgaard-Oeschger cycles in the annual-layer counted GISP2 ice core, with the major spikes reflecting the Heinrich events 1–6. This correlation indicates large fluctuations in the calibration of 14C ages between 20 and 54 14C ka bp. Generally the results confirm the 14C age shifts as predicted by the geomagnetic model of Laj, Mazaud and Duplessy (1996). However, the amplitude and speed of the abrupt decrease and subsequent major increase of our 14C shifts after 45 14C ka bp clearly exceed the geomagnetic prediction near 40–43 and 32–34 calendar (cal) ka bp. At these times, the geomagnetic field intensity minima linked to the Laschamp and the Mono Lake excursions and confirmed by a local geomagnetic record, probably led to a sudden increase in cosmogenic 14C and 10Be production, giving rise to excess 14C in the atmosphere of up to 1200%.

In this study we report on accelerator mass spectrometry (AMS) wiggle-match dating of selected macrofossils from organic deposits ca. 800 cal bc (ca. 2650 bp). Based on paleological, archaeological and geological evidence, we found that the sharp rise of atmospheric 14C between 850 and 760 cal bc corresponds to the following related phenomena:

1. 1. In European raised bog deposits, the changing spectrum of peat forming mosses and a sharp decline in decomposition of the peat indicate a sudden change from relatively dry and warm to cool, moist climatic conditions.

2. 2. As a consequence of climate change, there was a fast and considerable rise of the groundwater table so that peat growth started in areas that were already marginal from a hydrological point of view.

3. 3. The rise of the groundwater table in low-lying areas of the Netherlands resulted in the abandonment of settlement sites.

4. 4. The contemporaneous earliest human colonization of newly emerged salt marshes in the northern Netherlands (after loss of cultivated land) may have been related to thermal contraction of ocean water, causing a temporary stagnation in the relative sea-level rise.

Furthermore, there is evidence for synchronous climatic change in Europe and on other continents (climatic teleconnections on both hemispheres) ca. 2650 bp. We discuss reduced solar activity and the related increase of cosmic rays as a cause for the observed climatological phenomena and the contemporaneous rise in the 14C-content of the atmosphere. Cosmic rays may have been a factor in the formation of clouds and precipitation, and in that way changes in solar wind were amplified and the effects induced abrupt climate change.

The “wiggle-matching” technique has been widely used for the absolute dating of a series of radiocarbon-dated samples connected in one floating chronology. This is done by calculations of SS statistics (the mean-square distance of 14C ages of samples from the calibration curve) calculated for any assumed calendar age of the floating chronology. In the standard procedure the confidence intervals of true calendar age are derived from the width of the SS minimum, using the critical values of the chi-square distribution. This, however, seems oversimplified. Another approach is an extension of the Bayesian algorithm for calibration of single 14C dates. Here, we describe in detail the Bayesian procedure and discuss its advantages compared to the SS minimization method. Our calculations show that for given errors of 14C measurements, precision of dating the series is related to the shape of the SS curve around its minimum, rather than to the absolute value of SSmin. In some cases, dating precision may be improved more efficiently by extending the time span covered by the series rather than by improving the precision of the 14C measurements. The application of the Bayesian method enabled us to delimit the age of the floating varve chronology from the sediments of Lake Gościąż with distinctly better accuracy than was previously reported using the SS curve alone.

Application of radiocarbon dating to a short chronology is often limited by the wide probability ranges of calibrated dates. These wide ranges are caused by multiple intersections of the 14C age with the tree-ring curve. For a single unrelated 14C date, each intersection presents a probable solution. When several dates on different events are available, identification of the most probable solution for each event is possible if one can obtain some information on the relation between these events. We present here a method for such identifications.

To demonstrate the method, we selected a series of 14C dates from mortuary monuments of the Egyptian Old Kingdom. Corrected 14C dates from seven monuments were used. Calibration of these dates produced three absolute ages with single intersections and four ages with 3–5 intersections. These data are compared to a historical chronology, which places the dated events at a younger age. If each intersection is chosen as a potential anchor point of the “correct” chronology, 17 solutions must be tested for the best fit against the historical chronology. The latter is based on the length of the reign of each pharaoh during the studied time span. The spreadsheet has the function of determining the probability of fit for each of the solutions. In a second step the 17 probability values and their offset between the historical and the 14C chronology are graphically analyzed to find the most probable offset. This offset is then applied as a correction to the estimated chronology to obtain an absolute time scale for the dated events.

We present a radiocarbon chronology of key Sayan-Altai monuments from the Scythian period, based on a statistical analysis of dates produced in the 1980s and now supplemented with new dates. These new 14C dates were produced for samples from the Tuekta-1 barrows (burial mounds) and were measured both in St. Petersburg and Groningen. These tree-ring samples were fitted to the calibration curve. Chronologies were established for the Arzhan, Tuekta-1 and Pazyryk-5 barrows. The time of the construction of the Arzhan and Pazyryk-5 barrows is the 9th and late 5th–4th centuries bc, respectively, and agrees with archaeology. According to new data obtained, the time of the Tuekta-1 barrow construction is some years older than has been accepted thus far by archaeologists.