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  • AGU (American Geophysical Union)  (1)
  • American Institute of Physics (AIP)  (1)
  • Cambridge University Press  (1)
  • 2000-2004
  • 1990-1994  (3)
  • 1975-1979
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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 2485-2487 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Accelerator mass spectrometry (AMS) requires ion sources delivering intense negative ion beams of high stability. In addition, a multitarget system and a vacuum lock for sample loading are essential for efficient operation. We present a new design of a cesium (Cs) negative ion sputter source with the following features: the vacuum chamber of the ion source and the target cassette are at ground potential. Batches of targets can be loaded and unloaded without interrupting the operation of the source. All control systems for sample loading and automatic changing are also at ground potential. This ion source concept has already been successfully applied to AMS at our laboratory. The new design incorporates a spherical Cs surface ionizer to increase the negative ion currents. Difficulties in realizing this concept are the high electric fields inside the vacuum chamber in an environment with high Cs vapor pressure. Also critical are the proper and reliable operation of all mechanical components under these conditions and the large temperature gradients.
    Type of Medium: Electronic Resource
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  • 2
    Publication Date: 1993-01-01
    Description: A 34.5 m borehole, which was drilled near the Dead Sea coast (altitude -394 m) in the southern part of the fan delta of Wadi Zeelim, reveals the geological history of that area from the latest Pleistocene to present. The depositional time frame is based on six 14C dates and two U-Th dates. An erosional (or nondepositional) period is implied by the hiatus between 21,100 yr B.P. (U-Th age, depth 33 m) and 11,315 yr B.P. (14C age, depth 32 m). A subsequent arid phase is recorded by a 6.5-m-thick layer of halite; based on 14C dates this phase relates to the abrupt Younger Dryas cold period reported in temperate to polar regions. The fragility of the environment in this region is indicated by the fact that the region experienced such a severe, short aridification phase (less than 1000 yr), evidence of which is found widely in the desert fringes of the Middle East and North Africa. The aragonite found in most of the Holocene section indicates that the well site was covered by the lake for most of the Holocene. Exceptions are the intervals at 0-3 and 10-14 m depths which represent low stands of the lake.
    Print ISSN: 0033-5894
    Electronic ISSN: 1096-0287
    Topics: Geography , Geosciences
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  • 3
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    AGU (American Geophysical Union)
    In:  Paleoceanography, 6 (5). pp. 593-608.
    Publication Date: 2016-06-16
    Description: Radiocarbon ages on CaCO3 from deep-sea cores offer constraints on the nature of the CaCO3 dissolution process. The idea is that the toll taken by dissolution on grains within the core top bioturbation zone should be in proportion to their time of residence in this zone. If so, dissolution would shift the mass distribution in favor of younger grains, thereby reducing the mean radiocarbon age for the grain ensemble. We have searched in vain for evidence supporting the existence of such an age reduction. Instead, we find that for water depths of more than 4 km in the tropical Pacific the radiocarbon age increases with the extent of dissolution. We can find no satisfactory steady state explanation and are forced to conclude that this increase must be the result of chemical erosion. The idea is that during the Holocene the rate of dissolution of CaCO3 has exceeded the rain rate of CaCO3. In this circumstance, bioturbation exhumes CaCO3 from the underlying glacial sediment and mixes it with CaCO3 raining from the sea surface.
    Type: Article , PeerReviewed
    Format: text
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