Search

A study of erosion rates by in-situ 10Be concentrations in granites of Miocene high-elevation paleosurfaces in Corsica indicates maximum erosion rates between 8 and 24 mm/kyear. The regional distribution of measured erosion rates indicates that the local climatic conditions, namely precipitation, the petrographic composition of granites, and the degree of brittle deformation govern erosion rates. Chemical erosion dominates even at elevations around 2,000 m in presently subalpine climate conditions. Field evidence indicates that erosion operates by continuous dissolution and/or disintegration to grains (grusification). The erosion rates are relatively high with respect to the preservation of inferred Early Miocene landscapes. We infer temporal burial in the Middle Miocene and significantly lower erosion rates in the Neogene until ∼3 Ma to explain the preservation of paleosurfaces, in line with fission track data. Valley incision rates that are a magnitude higher than erosion rates on summit surfaces result in relief enhancement and long-term isostatic surface uplift. On the other hand, widening and deepening of valleys by cyclic glaciation progressively destroys the summit surface relics.

The authors present a reconstruction of precipitation, seasonality, and vegetation cover over the period from 200 cal yr B.C. to 1600 cal yr A.D. for the archaeological site of Anse a la Gourde, Guadeloupe, based on the oxygen and carbon isotope composition of accelerator mass spectrometry (AMS) 14C-dated aragonitic shells of the landsnail Bulimulus guadaloupensis. The results show that the Late Cedrosan Saladoid population (400-800 cal yr A.D.) disappeared at the beginning of a dry and stormy period lasting from 800 to 1000 cal yr A.D. The Mamoran Troumassoid started to populate the site around 1000 cal yr A.D. when the climate became wetter, and remained until 1300 cal yr A.D. The snail-shell carbon isotope values changed significantly around the period that the Late Cedrosan Saladoid occupation started. This indicates a vegetational response either to the wetter conditions, or because of the replacement of existing C4 plant vegetation by introduced C3 crops.

CO2 and CO obtained by dry-extraction from ice samples of the EPICA Dome C core were 14C analysed by AMS. For some of the ice samples there is no evidence for in situ 14C, indicating the firn did not retain 14C. The 14C ages of these samples are too old in comparison with a calibrated ice-flow model, and the concentrations of 14CO are near zero. For other ice samples, however, in situ 14C is clearly present, and is likely from post-coring exposure at the Dome C surface. These samples show too young 14C ages, and distinct concentrations of 14CO. The accuracy of ages obtained from 14C analysis of ice samples is discussed.

A high-resolution atmospheric radiocarbon record has been obtained for the interval of 17–36 kyr from U/Th-dated aragonite sediment of Lake Lisan. Reservoir age corrections were applied with reservoir ages of 200, 1250, and 2000 yr, which correlate with the different water levels of the lake. The present 14C record for Lake Lisan shows near resemblance with that of Lake Suigetsu: both converge to the value of Δ14C ∼0‰ at 32 kyr cal BP. Both also show significant differences compared to other reported high-resolution 14C records (e.g. Iceland Sea, Cariaco basin, and Bahamas speleothem). This inconsistency should be addressed by re-assessment of the basic assumptions behind the determination of calendar ages of the various records.

Sub-fossil sections from a Florida wetland were accelerator mass spectrometry (AMS) dated and the sedimentological conditions were determined. 14C data were calibrated using a combined wiggle-match and 14C bomb-pulse approach. Repeatable results were obtained providing accurate peat chronologies for the last 130 calendar yr. Assessment of the different errors involved led to age models with 3–5 yr precision. This allows direct calibration of paleoenvironmental proxies with meteorological data. The time frame in which 14C dating is commonly applied can possibly be extended to include the 20th century.

Basal peat age–depth data from four salt-marsh sites located 500–1500 m south of the Eastern Border fault (EBF) near Branford, Connecticut, document an error envelope for the lower limit of relative mean high water (MHW) rise during the past 3300 yr. The long-term rate of relative lower-limit-MHW rise during the past 3000 yr (1.1 mm yr −1 ) corresponds with late Holocene rates of relative MHW rise found elsewhere in coastal Connecticut (0.9–1.2 mm yr −1 ). This result invalidates repeated claims that multiple seismotectonic lowering of a crustal block towards the south has occurred along a segment of the EBF near Branford shortly after 815 cal yr BC and during the past 1200 yr and calls for a non-tectonic interpretation of biostratigraphic evidence of local short-term sea-level variations.

Airborne carbonyl compounds have been sampled at three European semi-remote to semi-urban test sites for radiocarbon ( 14 C) analysis. The used methodology included collection on 2,4-dinitrophenylhydrazine coated silica gel cartridges, chromatographic isolation of the formed hydrazones, combustion into CO 2 , reduction into graphite followed by accelerator mass spectrometry. In combination with this, liquid chromatography coupled to atmospheric pressure chemical ionisation mass spectrometry was used for chemical speciation of the collected carbonyls. At all sites the carbonyls were found to be of a mixed biogenic/anthropogenic origin. The determining factor for the proportion of fossil (anthropogenic) carbon in the samples was the vicinity of urban sources for carbonyls and their photochemical precursors. At meteorological conditions, which gave the test sites semi-rural/semi-remote characteristics the samples contained an average of 24% (range: 10–34%) of fossil carbonylic carbon. When air masses were transported from urban areas to the test-sites significantly higher proportions of fossil carbonylic carbon were determined with a maximum of 61%. Principal component analysis on this limited data set indicated that a low fossil proportion of carbonylic carbon is associated with high proportions of acetaldehyde, acetone, pentanone and acrolein. Until further radicarbon studies are carried out the conclusion remains that for the carbonyl compounds measured European background levels are of a predominant biogenic origin.

Comparison of two sets of marsh-accumulation records from each of three Connecticut (USA) salt marshes, one based on individually calibrated dates and the other on wiggle-match dating of the same series of dates, shows that wiggle-match dating results in more precise and objective reconstructions of longer-term (102–103 yr) changes in accumulation rate. On (sub-)century time scales, wiggle-match dating can reveal steps in the calibrated marsh-accumulation envelope as artefacts of the calibration curve, but may also leave real short-term changes in accumulation rate undetected. Wiggle-matches are non-unique, being dependent on the number, quality and distribution of radiocarbon dates in a sequence, how a series of dates is subdivided into groups (representing intervals of uniform accumulation rate), and what is considered a “best match”. Samples from the studied salt-marsh deposits required no correction for reservoir effects prior to calibration.

Variability in surface and deep ocean circulation in the North Atlantic is inferred from grain-size characteristics and the composition of terrigenous sediments from a deep-sea core taken on Reykjanes Ridge, south of Iceland. End-member modeling of grain size data shows that deep-ocean circulation in this area decreased significantly during periods of maximum iceberg discharge. The episodes of reduced circulation correlate with the cold and abrupt warming phases of the Dansgaard-Oeschger cycles as recognized in the Greenland ice cores.

Modifications of the Utrecht AMS set-up have resulted in 14C analysis with a routine 0.4% analytical precision and a detection limit of 2.0 × 10−15. In analysis with 10Be, 26Al and 36Cl the precision is a few percent and the detection limit 10−14. Measurements on small carbon samples (< 0.4 mg) revealed a sample-mass dependent isotope fractionation effect, which together with the background limits the precision for the smallest samples (0.02 mg) to a few percent.

We quantified the rate of carbonate dissolution with increasing water depth by taking the difference in the carbonate mass accumulation rate of deep (3393–4375 m) core top sediments from the shallowest one (3208 m), which we assumed was unaffected by dissolution. This method depends on high quality14C dates that we calibrated to calendar years for calculating sedimentation rates. Our results show low (ranging from 0 to 0.3 g cm−2ka−1) and high (ranging from 1.5 to 1.7 g cm−2ka−1) carbonate dissolution rates, above and below 4000 m, respectively. Therefore, we interpret the sudden increase in the carbonate dissolution rate at 4000-m water depth to mark the lysocline.

A fossil pollen record from the Costa Rican Cordillera de Talamanca presents the first AMS radiocarbon-dated evidence of a temperature decrease during the Younger Dryas Chron. This cooling event is named La Chonta stadial after the bog at 2310 m altitude, located at the actual lower to upper montane forest boundary. High-resolution pollen analysis revealed that between 11,070±130 (AMS 14C age) and 10,400 yr B.P. (interpolated age) vegetation comparable to present-day subalpine forest occurred about 300–400 m lower than in the previous warmer interval, and 600 to 700 m lower than at present time. The radiocarbon dates are close to the earlier estimated ages of 11,080-10,500 yr B.P. for this interval, based on interpolation and pollen concentration rates (Hooghiemstra et al., 1992). The downslope shift of the upper forest line indicates an estimated temperature drop of 2–3°C during the La Chonta stadial. The local vegetation development is indicative of a drier climate. From 10,400 to 9800±120 yr B.P. (AMS 14C age) subalpine rain forest was replaced by upper montane forest, a transitional period to Holocene environmental conditions.

Shallow ice cores from an Antarctic blue-ice area at Scharffenbergbotnen were l4C-analyzed using a dry-extraction technique and accelerator mass spectrometry. The in situ production was determined from the 14CO component and used to deduce the natural 14CO2 component. The ages were measured at 10 000 ± 3000 BP. The accumulation and ablation rates determined from the in situ production are 7–20 and 10 cm a−1. respectively, showing agreement with field observations. The derived ages and air-yield data show a nearby origin for the surface ice.

We use a dry extraction method to obtain trapped CO2 of shallow ice cores from a blue ice area of East Antarctica. In-situ-produced 14C extracted in 14CO2 and 14CO concentrations show a mean ratio of 3.4 ± 0.4. Correction for in-situ14CO2 resulted in ice ages within 7–13 ka. The accumulation and ablation rates determined from the in-situ production of 7–20 cm yr−1 and 10–13 cm yr−1, respectively, agree with field measurements, and thus indicate close to total efficiency of extraction.

14 C analysis of material from the shells of Arctica islandica supports the hypothesis that the clear and definite bandings of these shells are annual rings. The pulse of 14 C around 1960, resulting from atmospheric nuclear-bomb testing was recorded in the shell at a location in concurrence with that expected from band counting. The observed cyclic variation in stable isotopes of oxygen and carbon coincided with growth bands. This variation, at least for 18 O, agreed with annual temperature variations and suggests that growth bands are a reflection of seasonally determined differential growth rates. The longevity of individuals of this species, coupled with variations in band width, may provide important information regarding growth and productivity, as well as a record of past environmental conditions.

A dry extraction method was used to obtain trapped CO2 of 2–5 kg ice samples from a blue ice zone in East Antarctica. In situ produced 14C was also extracted in 14CO2 and 14CO concentrations at a ratio of 3.4 ± 0.9. Correction of trapped 14CO2 from in situ resulted in ice dates in the range 5–15 ka. The realistic rates for accumulation and ablation of ice indicate about total efficiency of extraction.

The 10 Be activites in 21 diogenites vary from 17 to 27 dpm/kg. These variations can primarily be ascribed to shielding effects, as was deduced from their correlation with the 22 Ne/ 21 Ne ratio. The 10 Be production rates in small diogenites are 10–30% higher than was predicted by a semi-empirical model based on the Knyahinya chondrite. This implies that 10 Be is less shielding dependent than expected. Our first AMS measurements of 26 Al in chondrites agree with earlier 26 Al γ-ray results.

Jorissen, F.J., Asioli, A., Borsetti, A.M., Capotondi, L., De Visser, J.P., Hilgen, F.J., Rohling, E.J., Van der Borg, K., Vergnaud Grazzini, C. and Zachariasse, W.J., 1993. Late Quaternary central Mediterranean biochronology. Mar. MicropaleontoL, 21: 169-189. A high-resolution biochronology is presented for the Late Quaternary of the central Mediterranean. In the Late Pleistocene-Holocene successions three assemblage zones are distinguished on the basis of frequency patterns of planktic foraminifera. The age of these zones is determined by Accelerator Mass Spectrometry (AMS) t4C dating. The zonal boundaries are dated at 12,700 yr B.P. (the end of Termination la) and 9600 yr B.P. (the start of Termination Ib), respectively. The AMS dates show that major changes in the planktic and benthic realms occurred synchronously over wide areas, although records of individual species may show important regional differences. In the studied areas, resedimentation processes revealed by anomalous successions of 14C dates, play a far more important role than indicated by the sedimentological and micropaleontological data. Possibly these processes contribute to the very high accumulation rates in the glacial Zone IlL Although the AMS technique has increased the accuracy of laC-measurements, of older carbonate may still lead to substantial age differences between areas with different sedimentary regimes.

The applicability of a (gas filled) spectrograph in elastic recoil detection analyses is discussed. We have optimized the experimental parameters for the determination of low oxygen concentration in hydrogenated amorphous Si. We demonstrate that for this case the value for the detection limit is well below 0.05 at.%.

The accretion rate of manganese nodules and the sedimentation rate of the underlying sediment has been studied with 10 Be and 14 C on a nodule covered hill in the Madeira Abyssal Plain. The accretion rate of (3.2±0.6) mm/Ma for the nodules is considerably smaller than the average sedimentation rate of 12 mm/ka for the last 50–100 ka. The mechanism that kept the nodules at the surface in this specific environment during the last 40 ka is likely to be flotation. The discovery of a large manganese-covered concretion in a piston core points to a long period of sediment winnowing. The 14 C analyses also seem to point to an increase in the sedimentation rate round 6500 yrs B.P.

The level of the Caspian Sea, the largest inland sea in the world, has fluctuated capriciously in history, with amplitudes up to 3 m in the last century, to 25 m in the last millennium, and to over 150 m since the Last Glacial. There is little consensus about the causes, and forecasts are contradictory, mainly due to a lack of solid data about past sea levels before 1837 AD, when instrumental observation started. We studied the Holocene Turali barrier complex along the western Caspian shore in Dagestan, Russia. Barrier dynamics during the last 3 m sea-level cycle in the past century show that only lagoonal deposits overridden by highstand barriers are suitable for dating former highstands. In the Holocene barrier complex, we selected the most suitable sites for dating using ground penetrating radar (GPR) profiles, outcrops and gravel pits. We obtained 14 accelerator mass spectrometry (AMS) 14C data on in situ double-valved molluscs from highstand lagoonal deposits. The results suggest that the last major highstands occurred around 2600 BP and in the Little Ice Age and coincide with global cooling events associated with minima in solar activity. This suggests that millennial precipitation changes in the Volga River drainage basin are also forced by solar activity.

Deep inside the Frasassi cave complex in the foreland fold and thrust belt of the northeastern Apennines (central Italy), the remains of hundreds of eels (Anguilla anguilla) are found scattered on the shores of phreatic lakes up to 5 m above the water table. These sub-fossil eels, and the speleothemic calcite encrusting some of them, offer the rare opportunity for radiocarbon dating leading to a geochronologic scale for the shorelines, which record the lowering of the water table and the uplifting of the Frasassi area through the Holocene. The lakes' margins are contoured by white microcrystalline calcite rinds, which also record the progressive lowering of the water table. Detailed surveying revealed that these rinds are no longer horizontal, but slightly tilted toward ENE. Thus these rinds record a recent history not only of uplifting, but also of tectonic tilting of this region. The results of our analyses indicate that the Apennine area around Frasassi has been rising, for the past 8000 years, at a mean rate of 0.6 mm/yr, which is consistent with uplifting rates estimated from the step topography arrangement of interglacial fluvial terraces for the whole Quaternary period in this region. This work demonstrates how an interdisciplinary approach to speleologic research can provide a significant contribution to active tectonic studies. © 2007 Elsevier B.V. All rights reserved.

Met lit. opg

Samples of a core (52 m) of ablating Antarctic ice were analysed for 14CO and 14CO2 by accelerator mass spectrometry. The data were compared with a 14C in situ production model that includes muon capture in addition to oxygen spallation by neutrons. The analysis reveals significant in situ14C at depths below 10 m, which we attribute to 14C production by cosmic ray muons. The age of the ice was determined as 9.3±0.4 14C ka BP.DOI: 10.1034/j.1600-0889.2002.00274.x

The pollen record of a 65 cm long core Laguna Carimagua–Bosque (4°04′N, 70°13′W) shows the late Holocene environmental history from a lake located within the gallery forest of the savannas of the Llanos Orientales of Colombia. Nine AMS radiocarbon dates of the organic deposits show that the core represents the period from ca. 1300 14 C yr BP to the present. The lake evolved from an active drainage system. During the period from ca. 1300 to 875 14 C yr BP (zone CMB-Ia), Mauritia -dominated swamp and gallery forest was present, dominated by Cecropia , and later also Acalypha and Alchornea . From 875 to 700 14 C yr BP (zone CMB-Ib), the lake was completely surrounded by gallery forest. Mauritiella and Cecropia occurred around the lake. Cecropia pioneer forest reached its greatest abundance and became gradually replaced by a more species-rich gallery forest, including Acalypha , Alchornea , Euterpe / Geonoma , Moraceae/Urticaceae, Piperaceae, and Virola . From 700 to 125 14 C yr BP (zone CMB-II), Cecropia lost its dominant role, and Mauritiella palms became more frequent. The main vegetation categories were swamp forest, gallery forest, understory elements, savanna shrubs and trees, and grass savanna. From 125 14 C yr BP to recent (zone CMB-III), the plant diversity in the gallery forest became highest, Mauritiella became very abundant, and among the savanna elements, woody Didymopanax increased. Comparison of four pollen records from savanna sites shows that pollen of savanna vegetation is markedly underrepresented in lake sediments when the lake lies within the gallery forest. As most of the drainage system of a savanna is hidden by gallery forest, we also expect a significant underrepresentation of the savanna ecosystem in river-transported pollen assemblages.

Institute of Meteorology and Oceanography, and ” Robert J. Van de Gruff Latwrarorium, University of Urrechr. Prmcetonplern 5, 3H4 CC Utrechr. The Netherlands “I Alfred- Wegener-Institut for Polar and Marine Research, Columhuutrasse, D-2850 Bremerhaven, FRG For 14C dating of ice, only a limited amount of CO, is available (20-100 pg C/kg ice). To avoid contamination. a special milling device has been constructed to chip the ice at - 20 o C. The background of 7.0 + 2.0 percent modem carbon (pmC) for a sample of 50 pg C, including extraction and conversion, limits the 14C dating of ice with accelerator mass spectrometry (AMS) to about 20000 years

A dry extraction method of CO 2 included in glacier ice adds a contamination equivalent to 1.8 μg modern carbon for a 35 μ g C sample. This enables radiocarbon dating by accelerator mass spectrometry of 35 μ g C samples to about 25 000 BP. Measured 14 C/ 12 C ratios are presented for a part of the Vostok ice core, and for some surface samples; high 14 C/ 12 C values ranging between 65 and 105 pin C indicate in-situ 14 C production during the ablation. The reproducibility of radiocarbon dating of ice is demonstrated by results for some parts of the Caroline core, yielding an age versus depth profile, in which the age does not simply increases with depth. The results indicate that the accuracy of radiocarbon dating of ice is not limited by the statistical error arising in the accelerator measurements, but by the uncertainty in the contamination background of the samples and by the in-situ production of 14 C. DOI: 10.1034/j.1600-0889.1994.t01-1-00002.x

The Utrecht facility for accelerator mass spectrometry is described. The set-up with an EN tandem accelerator is designed for measurements of a broad range of long-lived radionuclides and of stable trace elements. In particular, dating measurements with 10Be and 14C can be performed with high precision by rapid switching between the measurements of the isotopes. Optimal beam transmission through the accelerator is achieved with a new injection system in conjunction with the installation of axially symmetric acceleration tubes with spirally inclined electrodes. The first 14C/12C measurement with this set-up is reported.

Direct comparison of data for 12 C (α, p ) 15 N and 16 O (α, p ) 19 F allows the identification of 3p4h states in 15 N with J = 5 2 + , 9 2 + and 13 2 + . Correspondence between 19F and 15N is very good, in both transfer strengths and excitation energies.

Kau Bay is a small marine basin in between the two northern arms of the Island of Halmahera (Indonesia), separated from the adjacent Philippine Sea by a sill of 40 m deep. Microfossil and radiocarbon data of piston cores indicate that Kau Bay was a freshwater lake in Weichselian times. At 10 ka BP, the Bay became reconnected with the open ocean. Present-day deep water in Kau Bay is poorly ventilated because the sill limits water exchange with the adjacent ocean. Ventilation occurs through occasional inflow of denser oceanic water, but when this fails oxygen depleted conditions rapidly arise. The permanent presence of oxygen tolerant deep water benthic foraminifers over the past 10 ka indicates that dysoxic conditions prevalied and that anoxic conditions, as observed during the Snellius-I Expedition (May 1930), apparently existed for a short time only and left no trace that could be resolved with our time-resolution of 35 years. Slight and long-term variations in the degree of oxygen deficiency most likely are caused by long-term changes in the density of inflowing oceanic water, possibly in consequence of climatic oscillations. The homothermal surface water of Kau Bay shelters a low-diversity planktonic foraminiferal fauna of primarily shallow-dwelling species. This specific association extends back over the past 8 ka indicating that surface waters remained homothermal over much of the Holocene. Surface water productivity most likely changed with variations in river discharge.

The cross sections for excitation of the members of the ground state (g.s.) band 0 − (g.s.), 2 + (1.37 MeV) and 4 + (4.12 MeV) and the γ-band 2 + γ (4.24 MeV), 3 γ + (5.24 MeV) and 4 γ + (6.01 MeV) in 24 Mg have been measured in inelastic α-scattering at E α = 120 MeV. The excitation of these states are found to be well described by a coupled-channel calculation (CCBA) performed in the framework of the asymmetric rotational model. Two sets of parameters are found to give excellent fits to the data, but in both a direct coupling between the ground state and the 4 + state is found necessary.

Maps of accumulation rates of freshwater diatoms and opal phytoliths in the surface sediments of the Zaire fan show that both types of microfossils were supplied to the ocean floor by the Zaire River, and that opal phytoliths also have a southern source, probably the region of the Namibian desert. The PhFD ratio, of opal phytoliths to freshwater diatoms, can be regarded as an aridity index for equatorial Africa, and probably for large parts of the central and southern Atlantic. In two cores, the record of the PhFD ratio indicates humidity ca 225–190 ka BP, aridity 190–135 ka BP with maxima ca 170 and 140 ka BP and a humid excursion 150 ka BP, an increase in humidity 115 ka BP, a less humid period 90–30 ka BP, more humidity ca 30–17 ka BP with possibly more arid intervals ca 22.5 and 20 ka bp. In general, glacial (sub) stages were more arid and interglacial (sub) stages more humid. For the last 20 ka, the PhFD ratio corresponds closely with the known climatic events in tropical Africa.

Symmetric fission of 24 Mg into two 12 C nuclei following inelastic scattering of 120 MeV α-particles has been studied. The 12 C g.s. + 12 C g.s. and the 12 C g.s. + 12 C(4.44 MeV) decay modes were identified in the excitation energy ranges of 24 Mg, 22 MeV ≦ E x ≦ 26 MeV and 25 MeV ≦ E x ≦ 32 MeV, respectively. Depending on the assumptions made about the α'-inclusive spectrum, lower and upper limits have been obtained for the average partial width 〈 Γ CC / Γ 〉.

The inelastic α-scattering reaction at Eα = 120 MeV with an energy resolution of 90–150 keV has been used to investigate isoscalar strength distributions in 24, 26Mg, 28Si and 40Ca. For 24, 26Mg and 28Si the E2 strength between Ex = 14 and 27 MeV is strongly fragmented. In 40Ca the E2 strength is mainly concentrated near E x ~ 65 A 1 3 MeV, although here the onset of fragmentation can be observed. The sum rule strength for the different multipolarities was obtained by applying for each nucleus an L-dependent normalization procedure. In this way we observed in total in 24, 26Mg, 28Si and 40Ca for excitation energies up to 27 MeV an amount of (61+8−6), (50+9−8), (38+8−6) and (94 ± 14)%, respectively, of the isoscalar E2 energy weighted sum rule (EWSR) of which (36+7−5), (28+8−7), (24+7−5) and (74 ± 12)% was found between Ex = 14 and 27 MeV. In addition isoscalar E0, E3 and E4 strength was observed in this excitation energy region. A detailed comparison has been made between the isoscalar quadrupole strength distribution observed in the 24, 26Mg(α, α') reaction and the E2 strength excitation function obtained from radiative α-capture measurements. In the low excitation energy region coupled channel effects have been observed, especially for the excitation of the 3+ states. Moreover, a considerable percentage of the 1ħω isoscalar dipole and octupole strength has been observed for excitations below 14 MeV.

The distribution of giant quadrupole resonance strength in /sup 24,26/Mg obtained from inelastic ..cap alpha..- and proton-scattering experiments and ..cap alpha..-capture experiments have now been shown to be compatible. The results show that the giant quadrupole resonance strength in /sup 24/Mg and /sup 26/Mg is fragmented into several states or clusters of states and suggest that the giant quadrupole resonance states have very different ..cap alpha../sub 0/-decay strength.

Structure corresponding to various multipolarities is observed in the giant resonance region of 28 Si in inelastic α-particle scattering at E α =120 MeV. In this region (27 ± 6)% of the isoscalar quadrupole energy weighted sum rule (EWSR) is exhausted. Evidence for a monopole state at 15.9 MeV exhausting 3.2% of the E0 EWSR is presented.

During an excavation of 1986 and 1987, a joint team from Utrecht, Siena and the Soprintendenza di Sassari e Nuoro, found a pre-Neolithic lithic industry in Corbeddu Cave, Oliena, Sardinia, which was dated to 8000–17,000 bp. The artifact typology is different from that of the mainland of the same period. The lithic and bone artifacts suggest an endemic isolated economy of the Upper Pleistocene in Sardinia.

Human fossils found in a Pre-Neolithic cave deposit (Corbeddu cave, Sardinia) represent the first human remains associated with an endemic impoverished island fauna. Radiocarbon dating by AMS in Utrecht provided the chronological framework of the cave sediments for better understanding of the time-related human activities. The aberrant morphology of the human fossils and the unique character of worked deer bones discovered, suggest the development of an endemic Pleistocene human culture, adapted to the restricted island conditions and the hunting of ochotonids and deer.

The decay by protons and ..cap alpha..'s of /sup 24/Mg and /sup 40/Ca excited to an energy region from about 10 to 30 MeV has been studied in an (..cap alpha..,..cap alpha..'c-bar) experiment at E/sub ..cap alpha../ = 120 MeV. A strong increase of forward-backward asymmetry as a function of E/sub x/ starting at E/sub x/ = Q value+Coulomb barrier has been found for almost all decay channels studied indicating that this asymmetry is due to interference between the decay of the giant resonance structures and direct knockout processes.

Differential cross sections for the (p, t) reaction to 0+ states in the even Ge isotopes have been measured at an incident energy (Ep = 13 MeV) where the triton energy is below the Coulomb barrier. The data are described by a coupled-channels calculation with wave functions consisting of neutron configurations only. Sequential transfer processes can explain the anomalies, which have led previously to the introduction of shape isomerism or proton excitations.

10Be concentrations were measured in 20 (hemi)pelagic core top samples with an age control partly based on AMS 14C datings. The 10Be concentrations do not show any dependence on the bulk mass accumulation rates (MAR), but there is a significant linear correlation between 10Be accumulation rates and MAR. This correlation is best explained by terrigenous 10Be supply modified by biologic scavenging and, of secondary importance, adsorption on particulate matter in the ocean surface water in the Zaire plume. The variable term of the linear regression function indicates a maximum 10Be concentration for the terrigenous component of 5 × 109 at.g−1, the constant suggests an oceanic 10Be precipitation of (100–530) × 106 at.cm−2 ka−1. A 500 ka long record of 10Be concentrations is in agreement with the predicted values, but short-term variations in MAR obscure the expression of a long-term break in MAR about 350 ka ago.

The Utrecht facility for accelerator mass spectrometry is now in operation for routine measurements of 14C and 10Be in natural samples. Sample preparation techniques have been introduced. A 1% precision for 14 C 12 C ratios is routinely achieved. In the last year, more than 500 samples have been prepared and measured for various applications in archeology, geology and paleontology.

An injector has been built to obtain improved beam transmission through the EN tandem. The injector has been provided with a 90° analysing magnet, m/Δm = 300, and 130 kV preacceleration. Beam optics calculations have been made for the injector and tandem. The injector has been equipped with a fiber optics control and data acquisition system.

A detailed comparison between inelastic α and p scattering in the giant resonance region of 24, 26Mg, 28Si and 40Ca shows that there is no evidence for ΔT = 1, E1 excitation in the (p, p′) spectra. This is consistent with DWBA calculations using a recently obtained isovector interaction potential.

This article describes the elements of the pulsed beam measurement system at the AMS facility in Utrecht, in particular the switched power supplies and the current integrator.

10Be measurements of samples from a (hemi)pelagic sequence of Middle Miocene to Lower Pliocene age (Java, Indonesia) allow estimating the rate of sedimentation and the timespan during which deposition occurred. Large variations of 10Be values between adjacent samples can be satisfactorily ascribed to short term variations of the rate of sedimentation, with in addition downslope mass transport of sedimentary units that had previously been deposited higher on the submarine slope.

In the radiocarbon accelerator mass spectrometry (14C AMS) analysis of gases obtained in a dry extraction from a 52–m Antarctic ice core, we observed 14CO2 and 14CO concentrations decreasing with depth. The concentrations are explained in terms of in-situ production by neutrons and captured muons in ablating ice. The ratio of the 14CO2 concentration to that of 14CO has been found to be constant at 1.9 ± 0.3. The ablation rates obtained of 42 ± 18 cm.yr−1 and 40 ± 13 cm.yr−1 for the neutron and muon components, respectively, are about three times higher than observed from stake readings. The discrepancy may point to an incomplete extraction of the dry extraction method. Using the constant ratio in 14CO2 and 14CO concentrations we correct for the in-situ component in the trapped 14CO2 and deduce an age of 10,300 ± 900 BP for the ice core.