Göran Skog

Pitfalls in the AMS radiocarbon-dating of terrestrial macrofossils

The AMS 14 C technique has the advantage that small samples of Late Quaternary age can be dated with high accuracy, and that errors due to reservoir effects can be avoided if specifically determined terrestrial micro- and macrofossils are measured. However, to obtain such high-accuracy measurements, it is important how small samples are handled prior to treatment in the radiocarbon laboratories. Here we present a set of 51 AMS 14 C measurements, of which 31 dates gave expected ages and 20 dates resulted in anomalously young ages, despite the fact that all samples consisted of clearly identified Late Weichselian terrestrial plant macrofossils. To evaluate possible sources of error, we compared these samples in respect to preparation methods, sample storage and sample weight. Our results show that the long-term storage of wet macrofossil samples appears to have a significant effect on the radiocarbon age obtained, even when the samples are kept cool. Fungi or micro-organisms may easily be incorporated into a sample during preparation and identification, and can easily contribute to the contamination of a sample, if stored cool and wet for several months.

Consistently large marine reservoir ages in the Norwegian Sea during the Last Deglaciation

With the exception of the GS-1/Younger Dryas coldperiodmarine reservoir ages for the Last Deglaciation in the North Atlantic– Norwegian Sea are generally assumed to have been around 400–500 radiocarbon years in magnitude (Earth Planet. Sci. Lett. 126 (1994) 275; Radiocarbon 37 (1995) 53; Quat. Res. 52 (1999) 104; Nature 412 (2001) 724). By comparing the climate records obtained from the GRIP ice-core (Nature 359 (1992) 311; J. Quat. Sci. 13(4) (1998) 283) andfrom North Atlantic/Norwegian Sea cores (Quat. Res. 52 (1999) 104; Geology 23 (12) (1995) 1059; Nature 356 (1991) 757; Nature 356 (1992) 757; Paleoceanography 3(1) (1988) 1; Nature 343 (1990) 612; Earth Planet. Sci. Lett. 126 (1994) 275), with radiocarbon-dated European continental records, we show that marine reservoir ages in the Norwegian Sea were of the order of 1000 14 C yr, including large uncertainties. This approach rests on the reasonable assumption that climate changes throughout the NE Atlantic andEurope were more or less synchronous at the centennial scale. Fairly large variations in reservoir ages over time may have been causedby changing atmospheric 14 C content. The results indicate that detailed land-sea correlations for the North Atlantic during the Last Deglaciation are not feasible using radiocarbon dating alone. r 2003 Elsevier Science Ltd. All rights reserved.

Levels of 14C in the Terrestrial Environment in the Vicinity of Two European Nuclear Power Plants

Radiocarbon is produced in all types of nuclear reactors. Most of the C-14 released into the environment is in the form of gaseous emissions. Recent data on the C-14 concentration found in terrestrial samples taken in the vicinity of nuclear power plants in Romania and Lithuania are presented. We found increased C-14 levels in the surroundings of both power plants. At the Romanian power plant Cernavoda, we found excess levels of C-14 in grass within a distance of about 1000 in, the highest C-14 specific activity being 311 Bq/kg C (approximately 28% above the contemporary C-14 background) found at a distance of 200 in from the point of release (nearest sampling location). At the Lithuanian power plant Ignalina, samples of willow, pine, and spruce showed a C-14 excess of similar magnitude, while significantly higher values were found in moss samples. The samples were analyzed at the accelerator mass spectrometry facility in Lund, Sweden. (Less)

Dating Components of Human Atherosclerotic Plaques

Rationale: Atherosclerotic plaques that give rise to acute clinical symptoms are typically characterized by degradation of the connective tissue and plaque rupture. Experimental studies have shown that mechanisms to repair vulnerable lesions exist, but the rate of remodeling of human plaque tissue has not been studied. Objective: In the present study, we determined the biological age of different components of advanced human atherosclerotic plaques by analyzing tissue levels of 14C released into the atmosphere during the nuclear weapons tests in the late 1950s and early 1960s. Methods and Results: Atherosclerotic plaques were obtained from 10 patients (age 46 to 80 years) undergoing carotid surgery. Different regions of the plaques were dissected and analyzed for 14C content using accelerator mass spectrometry. At the time of surgery, the mean biological age of the cap region was 6.4±3.2 years, which was significantly lower than that of the shoulder region (12.9±3.0 years, P<0.01), the interface toward the media (12.4±3.3 years, P<0.01), and the core (9.8±4.5 years, P<0.05). Analysis of proliferative activity and rate of apoptosis showed no signs of increased cellular turnover in the cap, suggesting that the lower 14C content reflected a more recent time of formation. Conclusions: These results show that the turnover time of human plaque tissue is very long and may explain why regression of atherosclerotic plaque size rarely is observed in cardiovascular intervention trials.

Application of accelerator mass spectrometry (AMS) for high-sensitivity measurements of 14CO2 in long-term studies of fat metabolism

Long-term measurements of 14C in CO2 expired after ingestion of 14C-labelled triolein were performed using accelerator mass spectrometry (AMS). About 30% of a given amount of 14C-labelled triolein was catabolized rapidly, while the remaining 70% had a very slow turnover. The study shows the potential of the AMS technique for the study of the long-term biokinetics of 14C-labelled pharmaceuticals. The AMS technique allows the administered activity to be reduced by several orders of magnitude without compromising the study. It may also allow studies of rare drug metabolites.

Biokinetics and radiation dosimetry for patients undergoing a glycerol tri[1-14C]oleate fat malabsorption breath test.

The glycerol tri[1-14C]olein test for fat malabsorption was carried out in two male volunteers and measurements of the loss of 14C in expired air, urine and faeces and the retention of 14C in biopsy samples of abdominal fat were made using accelerator mass spectrometry. Exhalation accounted for 73% and 55% of the administered activity and could be described by three-component exponential functions with halftimes of about 1h, 2 days and 150 days, respectively. Urinary excretion accounted for 24% of the administered activity, almost all during the first 24h after administration; about 2% was excreted in the faeces in 48h. The halftime of retention of 14C in fat ranged from 137 to 620 days. Absorbed dose calculations indicate that for a normal adult the largest dose, 1.5-7.0mGy/MBq is received by the adipose tissue, and that the effective dose is 0.3-0.5mSv/MBq. It is concluded that no restrictions need to be placed on radiation safety grounds on the administration of 0.05-0.1MBq 14C-triolein for the triolein breath test.

Environmental levels of carbon-14 around a Swedish nuclear power plant measured with accelerator mass spectrometry

Abstract 14 C is one of the radionuclides which are produced by nuclear power plants. The main part of the 14 C, which is released during normal operation, is produced through neutron induced reactions in the cooling water and is released as airborne effluents (such as CO 2 and hydrocarbons) through the ventilation system of the plant to the surrounding environment. Because of the biological importance of carbon and the long half-life of 14 C, it is of interest to measure the releases and their incorporation into living material in the environment of the power plants. In this pilot study the accelerator mass spectrometry (AMS) facility at the University of Lund has been used to measure the 14 C activity concentration in vegetation around a Swedish nuclear power plant. AMS is suitable mainly because of the accuracy obtained within a short measuring time, which makes it possible to analyze a sufficient number of samples for a thorough investigation. The results of this study demonstrate that the AMS method is suitable for investigations of the influence on the local environment of reactor-released 14 C by analysis of living material. To test dispersion models, however, air sampling both of emission source and in the surrounding of the plant seems more suitable.

14C content in vegetation in the vicinities of Brazilian nuclear power reactors

(14)C specific activities were measured in grass samples collected around Brazilian nuclear power reactors. The specific activity values varied between 227 and 299 Bq/kg C. Except for two samples which showed (14)C specific activities 22% above background values, half of the samples showed background specific activities, and the other half had a (14)C excess of 1-18%. The highest specific activities were found close to the nuclear power plants and along the main wind directions (NE and NNE). The activity values were found to decrease with increasing distance from the reactors. The unexpectedly high (14)C excess values found in two samples were related to the local topography, which favors (14)C accumulation and limits the dispersion of the plume. The results indicate a clear (14)C anthropogenic signal within 5 km around the nuclear power plants which is most prominent along northeastwards, the prevailing wind direction.

14C levels in the vicinity of two swedish nuclear power plants and at two clean-air sites in Southernmost Sweden

(super 14) C is one of the radionuclides that are produced to different degrees by neutron-induced reactions in all types of nuclear reactors. Part of the (super 14) C created is continuously released into the surrounding environment during normal operation as airborne effluents in various chemical forms (such as CO (sub 2) , Co and hydrocarbons) through the ventilation system of the plant. Because of the biological importance of carbon and the long half-life of (super 14) C, it is of interest to measure the releases and their incorporation into living material. We report here on the (super 14) C activity concentrations in annual tree rings and the air around two Swedish nuclear power plants, as well as the background (super 14) C 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.

A new design for the low-energy optics of the Lund Pelletron accelerator

Abstract Several improvements have been implemented on the low-energy side of the Lund 3UDH Pelletron tandem accelerator. We report on the use of an ANIS sputtering source, the installation of a new injector with two legs and the rebuilding of the low-energy optics between sources and accelerator. New lenses have been placed at optimuum positions which, together with a higher pump capacity. increased the beamtransmission. Angular misalignment of the beam has been minimized by repositioning steerers and profile monitors.