Willy Wolfli

Radiocarbon in Atmospheric Carbon Dioxide and Methane: Global Distribution and Trends

For many years, there has been a growing concern in the field of atmospheric chemistry about anthropogenic and natural perturbations of the major atmospheric cycles of carbon, nitrogen and sulfur, and recently, oxygen. The concern is mainly due to the implications of these trace gases on global climate. In view of the atmospheric carbon cycle, the most abundant trace gases, carbon dioxide and methane, just recently became the subject of detailed 14C investigations. These may play an important role in providing the supplementary and independent information needed to better evaluate the current observations.

History of the paired lunar meteorites MAC88104 and MAC88105 derived from noble gas isotopes, radionuclides, and some chemical abundances☆

Abstract Noble gas isotopes, radionuclides, and chemical abundances were studied in the lunar meteorites MAC88104 and MAC88105 collected in the MacAlpine Hills area of Antarctica. The concentrations of the noble gas isotopes and the radionuclide activities in the two meteorites are essentially identical, proving that the two meteorites are paired. From 40K-40Ar dating we obtain a gas retention age of 3550 ± 400 Ma, typical for lunar surface material. Probably before breccia compaction the MAC88104/5 material resided for 630 ± 200 Ma at an average shielding depth of 85 g cm 2 , that is, about 50 cm below the lunar surface in the lunar regolith, as judged from the concentration of cosmic-ray produced Kr and Xe isotopes. Although this duration of lunar regolith residence is relatively long, MAC88104/5 represent immature regolith material: the concentration of solar wind implanted noble gases are two orders of magnitude lower than those in mature lunar soil. The reason for that might be the relatively high average shielding. The 40 Ar 36Ar ratio of the trapped component is 5.7 ± 1.0, indicating an intermediate antiquity of the material; we estimate that the solar wind and lunar atmospheric particles were implanted about 2000 Ma ago. The radionuclide activities allow us to derive the exposure history of the MAC88104/5 material. The duration of the Moon-Earth transfer was ≦0.24 Ma. Production of the radionuclides on the lunar surface immediately before ejection is possible, but duration and shielding depth for such an exposure cannot be determined from our data. We obtain a terrestrial age of 0.1 ≦ tterr ≦ 0.6 Ma and an ejection time of MAC88104/5 from the Moon of 0.1 ≦ tejection ≦ 0.8 Ma. The exposure histories of the lunar meteorites discussed in this work indicate that at least two impact events are required for their ejection from the Moon. Our first noble gas results for lunar meteorite Yamato-793274 show that it represents mature lunar regolith material with relatively high concentrations of solar wind implanted noble gases and a duration of several hundred million years of exposure to cosmic rays.

AMS measurements of thin-target cross sections for the production of 10Be and 26 Al by high-energy protons

Abstract In order to determine thin-target cross sections for the proton-induced prduction of residual nuclides from cosmochemically relevant target elements (Z≤28), irradiation experiments were carried out with energies between 100 and 2600 MeV at various accelerators. For p-energies below 200 MeV the stacked-foil technique was used, while for higher energies individual thin targets were irradiated at 600, 800, 1200 and 2600 MeV. Using accelerator mass spectrometry, cross sections for the production of Be from O, Mg, Al, Si, Mn, Fe and Ni and of 26Al from Al, Mn, Fe and Ni were measured. The experimental data are compared with earlier literature data and the present status of the respective excitation functions is discussed. Theoretical cross sections for the reactions investigated were derived by Monte Carlo calculations on the basis of an intranuclear-cascade/evaporation (INC/E) model using the HERMES code system. For energies below 200 MeV, hybrid model calculations were performed using the code Alice Livermore 87. The calculated and experimental data are compared and the different production modes of 10Be and 26Al are discussed.

High resolution 230Th and 10Be stratigraphy of late Quaternary sediments from the Fram strait (core 23235)

We obtained a high resolution stratigraphy of sediment Core 23235 (Fram Strait, 78°51,55′N, 01°18,59′E, 2456 m water depth) from the measurement of the concentration of 10Be and 230Th in depth profiles. The average sedimentation rate is approximately 3±0.3 cm/kyr. On a length of 806 cm the Core 23235 covers a time span of approximately 270 kyr. The profiles of the concentration of 10Be and 230Th have maxima during interglacials and minima during glacial periods. During the interglacials the fluxes of 10Be (up to 4.35±0.17 · 106 at cm-2 yr-1 and of 230Th (up to 26.70±6.37 dpm cm-2 yr-1) greatly exceed the depositional fluxes expected from the production of of 10Be in the atmosphere and 230Th in the water column. In contrast, during glacial stages 2 and 6 the 10Be fluxes are similar to or slightly lower than production fluxes, while the 23Th fluxes are significantly lower than the predicted flux. The only exception to this trend occurred during a short period of stage 6, at about 135 ka, which has the highest 230Th flux in the core record. At this ‘230Th flux anomaly’ the ratio of the production exceeding isotope fluxes of 10Be and 230Th has a value of 0.3:1, whereas during interglacial conditions this ratio approximates 4 : 1. We presume that the ‘230Th anomaly’ reflects a very short period of time during glacial stage 6, when renewal of deep water took place (it is generally assumed that no deep water was formed in the North Atlantic during stage 6). As a consequence of sudden oxygen supply to the water column at 135 ka, 230Th was scavenged from the water column with Mn-oxides more efficiently than 10Be.

10Be in the Atlantic ocean, a transect at 25° N

Abstract The 10Be concentration of the water column was measured on 5 profiles on a transect across the Atlantic at ≈ 25° N. In the deep water the profiles display a 10Be concentration of 1920 atoms g near the Mid-Atlantic Ridge, 1300 atoms g in the Western Basin, and 1300–1670 atoms g in the Eastern Basin, From this, the residence time of 10Be in the deep water can be calculated to 380–560 Ma. This agrees well with earlier estimates from the flux into sediments from the Eastern Basin. For the surface water, the residence time yields to 10–13 a.

High resolution 10Be and 230Th profiles in DSDP site 580

10Be and 230Th profiles were measured at Site 580 at a depth of 20 m (230Th and 10Be) and 80 m (10Be), corresponding to 360 ka and 1.5 Ma, respectively, with a resolution of approx. 5000 a. The radiometric sediment accumulation rates of 6.2 cmka ( ± 25%) agree well with the average for the last 730 ka (via paleomagnetic stratigraphy). Age corrected concentrations of 10Be range from 2 to 7 × 109atomsg (average 3.5 ± 1). The variations of the 10Be concentrations can be explained by changes in the sediment supply during different climatic conditions. The maxima and the minima of 10Be follow the fluctuations of excess 230Th in the core section during the last 360 ka. Fluxes of both 10Be and 230Th exceed production and vary remarkably throughout time suggesting enhanced scavenging by bioproductivity. At the Brunhess-Matuyama boundary we observe a maximum of 10Be (6.0 ± 0.3.109atomsg, corresponding to 2.5 σ deviation from the average value). However, the observed large fluctuations of Be-10 throughout the core profile make it difficult to interprete this particular maximum.

Evidence for primordial superheavy elements

X-ray analysis of monazite inclusions in micas from Madagascar surrounded by halos of abnormal size revealed several weak lines in the 22-28 keV region interpreted by Gentry et al. (1976) as Lalpha 1 lines of four superheavy elements. The observed structure in the spectra can, however, be explained as caused by K X-ray lines of the trace elements Rb, Sb and Te which are present in monazites and cheralites.

The manganese nodules of the Kane Gap (East Atlantic). Indicators of sedimentation — erosion changes

ZusammenfassungAn Manganknollen aus der Kane-Lücke, dem Verbindungskanal zwischen Sierra Leone Becken und Gambia Becken (vor W-Afrika) wurden entlang Querprofilen durch mehrere Knollen chemische Untersuchungen und10Be Altersbestimmungen durchgeführt. Durch Vergleich des Aufbaus der Knollen mit der Stratigraphie des unterlagernden Sediments werden Rückschlüsse auf Veränderungen des Sedimentationsgeschehens während der letzten 4–6×106 Jahre gezogen. Hiernach begann das Wachstum der Knollen vor maximal 4.5×106 Jahren während oder gegen Ende einer Erosionsphase auf fossilfreiem, vermutlich miozänem Sediment. Während der ersten Phase wuchsen die Knollen über wenige 100000 Jahre sehr schnell (7 bis>18 mm/106 Jahre). Hierbei schied sich Fe-reiche Knollensubstanz hydrogener Zusammensetzung ab. Nach Verringerung der Strömung und vermutlich zeitweiser Bildung von dünnen Sedimentschleiern änderte sich der Charakter der Knollen zu mehr diagnetischer Zusammensetzung bei wesentlich reduziertem Wachstum (ca. 1 bis 2 mm/106 Jahre). Der Zeitpunkt der Umstellung ist nur sehr grob zu ermitteln, er dürfte etwa zwischen 3 und 4×106 Jahren vor heute liegen.Eventuelle Unsicherheiten bei der Datierung und den Wachstumsraten, die möglicherweise aus milieubedingten Änderungen in der10Be Versorgung der Knollen resultieren, werden diskutiert.AbstractManganese nodules from the Kane Gap (a deep sea channel connecting the Sierra Leone and Gambia Basins off West Africa) were investigated chemically and dated by10Be along cross-sections. Comparing the nodule structure with the stratigraphy of the related sediments, the following conclusions are drawn concerning the sedimentation processes during the last 4 to 6×106 years: The growth of the nodules started about 4 to 4.5 Ma before present during or near to the end of a period of erosion on a fossil-free, probably Miocene sediment. During the first phase of only a few hundred thousandyears, the nodules grew very quickly (7 to >18 mm/Ma). Fe-rich hydrogenetic material formed the internal sections of the nodules during this time. Slowing down of the bottom currents, resulting in deposition of thin sediment covers for short intervals, caused the character of the nodules to change to a more diagenetic composition. The growth rates were reduced to about 1 to 2 mm/Ma. The time of slowing is roughly 3 to 4 Ma BP.Probable uncertainties of the dating and growth rates resulting from supposed changes of the10Be supply to the nodules due to variations of the near bottom environment are discussed.RésuméLe «Kana Gap» est un chenal sous-marin qui relie les bassins de Sierra Leone et de Gambie, au large de lAfrique occidentale. Des nodules de manganèse, recueillis le long de profils transversaux dans ce chenal, ont fait lobjet dune étude chimique et dune détermination dâge10Be. La comparaison entre la structure des nodules et la stratigraphie des sédiments sous-jacents permet de tirer les conclusions suivantes relatives au processus sédimentaire au cours des 4 à 6 derniers Ma. La croissance des nodules a commencé il y a environ 4 à 4,5 Ma pendant ou juste après un épisode dérosion sous-marine sur des sédiments non fossilifères, probablement miocènes. Au cours dune première phase dune durée de quelques centaines de milliers dannées, la croissance a été très rapide (7 à > 18 mm par Ma) avec formation de la partie centrale du nodule, constituée de matière hydrogénée riche en Fe. Ensuite, après ralentissement des courants de fond et dépôt probable dune mince couche de sédiment, le caractère des nodules a évolué vers une composition plus diagénétique, avec réduction du taux de croissance à 1 à 2 mm par Ma. Le moment de ce changement de régime doit se situer entre 3 et 4 Ma.Des changements dans les conditions de milieu sur le fond de la mer pourraient avoir provoqué une variation de la quantité de10Be apportée aux nodules, doù résulterait une incertitude sur lestimation des âges et du taux de croissance; cette question est discutée par les auteurs.Краткое содержаниеПровели химические и сследования и опреде лили возраст по10Ве марган цевых желваков, отобр анных вдоль поперечного пр офиля в проливе Кана, к оторый является каналом, сое диняющим бассейны Си ерры Леоне и Гамбии перед п обережьем западной А фрики. Сопоставление струк туры желваков и страт играфии подстилающих седиме нтов разрешило сдела ть вывод, что во время последни х 4х106–6×106 лет имели мест о изменения в процесса х седиментации. Рост ж елваков начался, самое раннее 4,5х106 лет тому назад во время и в конце эрозио нной фазы седимента, в ероятно, миоценового возраст а, свободного от фосси лий. Во время первой фазы ж елваки в течение неск ольких 100.000 лет росли очень быст ро: 7 до 18 мм за Ма. При этом образовалась ги дрогенная, богатая же лезом субстанция желваков. Когда течение измени лось, началось временное образован ие тонкослойных осад очных покровов, и характер ж елваков также измени лся в сторону биогенетич еского состава при бо лее замедленном росте их: от 1 до 2 мм за Ма. Время такого преобразования можн о установить только приблизительно, оно должно относится к периоду 3х106–4х 106 лет тому назад.Обсуждаются возможн ые неточности датиро вки и определения скорост и роста, которые, возмо жно, обусловлены изменен ием среды, из которой10Ве попадал в желваки.

Evidence for a molecular REC-effect in heavy ion collisions

Anisotropy spectra of the MOK X-ray transitions have been measured in F-Al, Al-Al and Cl-Al collisions as a function of the projectile energy. The measurements at higher energies indicate a new molecular effect due to transitions from quasicontinuum states to the MO 1sσ-orbitals.

Application of 16O RBS to heavy compound materials

Abstract The use of RBS with a 16 O beam for the analysis of high T c -superconductors has been studied. The advantages of heavy ion RBS (HIRES) for the determination of the compound stoichiometry are discussed. Even with the use of silicon surface barrier detectors a greatly enhanced mass resolution for heavy target elements can be reached. Due to the larger mass separation the determination of the stoichiometric ratios is more precise and the profiling of the heaviest element can be extended to appreciably deeper regions below the sample surface than with 4 He RBS.