ORCID Profile
0000-0001-9781-6505
Current Organisations
Wayne State University
,
iThemba LABS
,
Helmholtz-Zentrum Dresden-Rossendorf
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Publisher: Elsevier BV
Date: 02-2023
Publisher: Elsevier BV
Date: 07-2023
Publisher: American Chemical Society (ACS)
Date: 08-05-0014
DOI: 10.1021/ES400026M
Abstract: (236)U was analyzed in an ombrotrophic peat core representing the last 80 years of atmospheric deposition and a minerotrophic peat s le from the last interglacial period. The determination of (236)U at levels of 10(7) atoms/g was possible by using ultraclean laboratory procedures and accelerator mass spectrometry. The vertical profile of the (236)U/(238)U isotopic ratio along the ombrotrophic peat core represents the first observation of the (236)U bomb peak in a terrestrial environment. A constant level of anthropogenic (236)U with an average (236)U/(238)U isotopic ratio of (1.24 ± 0.08) × 10(-6) in the top layers of the core was observed. Comparing the abundances of the global fallout derived (236)U and (239)Pu along the peat core, the post depositional migration of plutonium clearly exceeds that of uranium. However, the cumulative (236)U/(239)Pu ratio of 0.62 ± 0.31 is in agreement with previous studies on the global fallout uranium and plutonium. In the interglacial peat s les a (236)U/(238)U isotopic ratio of (3.3 ± 0.7) × 10(-12) was detected although this measurement is an upper limit, it constitutes a significant step forward in the experimental determination of the natural (236)U abundance and represents a true background s le for the ombrotrophic peat core.
Publisher: Elsevier BV
Date: 10-2021
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C3EM30910J
Abstract: The isotopic composition of plutonium ((239)Pu, (240)Pu, (241)Pu and (242)Pu) was investigated in a ∼0.5 m long peat core from an ombrotrophic bog (Black Forest, Germany) using clean room procedures and accelerator mass spectrometry (AMS). This sophisticated analytical approach was ultimately needed to detect reliably the Pu concentrations present in the peat s les at femtogram (fg) and attogram (ag) levels. The mean (240)Pu/(239)Pu isotopic ratio of 0.19 ± 0.02 (N = 32) in the peat layers, representing approximately the last 80 years, was in good agreement with the accepted value of 0.18 for the global fallout in the Northern Hemisphere. This finding is largely supported by the corresponding and rather constant (241)Pu/(239)Pu (0.0012 ± 0.0005) and (242)Pu/(239)Pu (0.004 ± 0.001) ratios. Since the Pu isotopic composition characteristic of the global fallout was also identified in peat s les pre-dating the period of atmospheric atom bomb testing (AD 1956-AD 1980), migration of Pu within the peat profile is clearly indicated. These results highlight, for the first time, the mobility of Pu in a peat bog with implications for the migration of Pu in other acidic, organic rich environments such as forest soils and other wetland types. These findings constitute a direct observation of the behaviour of Pu at fg and ag levels in the environment. The AMS measurements of Pu concentrations (referring to a corresponding activity of (240+239)Pu from 0.07 mBq g(-1) to 5 mBq g(-1)) essentially confirm our a priori estimates based on existing (241)Am and (137)Cs data in the investigated peat core and agree well with the global fallout levels from the literature. Exclusively employing the Pu isotope ratios established for the peat s les, the date of the Pu irradiation (AD 1956, correctable to AD 1964) was calculated and subsequently compared to the (210)Pb age of the peat layers this comparison provided an additional hint that global fallout derived Pu is not fixed in the peat column, but has migrated downwards along the peat profile to layers preceding the nuclear age.
Publisher: Springer Science and Business Media LLC
Date: 12-2002
Publisher: Elsevier BV
Date: 05-2014
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 06-2023
Publisher: Cambridge University Press (CUP)
Date: 2012
DOI: 10.1071/AS11070
Abstract: An enhanced concentration of 60 Fe was found in a deep ocean crust in 2004 in a layer corresponding to an age of ∼2 Myr. The confirmation of this signal in terrestrial archives as supernova-induced and the detection of other supernova-produced radionuclides is of great interest. We have identified two suitable marine sediment cores from the South Australian Basin and estimated the intensity of a possible signal of the supernova-produced radionuclides 26 Al, 53 Mn, 60 Fe, and the pure r -process element 244 Pu in these cores. The finding of these radionuclides in a sediment core might allow us to improve the time resolution of the signal and thus to link the signal to a supernova event in the solar vicinity ∼2 Myr ago. Furthermore, it gives us an insight into nucleosynthesis scenarios in massive stars, condensation into dust grains and transport mechanisms from the supernova shell into the solar system.
Publisher: Elsevier BV
Date: 12-2012
Publisher: Informa UK Limited
Date: 10-06-2020
Publisher: Elsevier BV
Date: 10-2015
Publisher: Elsevier BV
Date: 06-2007
Publisher: Elsevier BV
Date: 2017
Publisher: Elsevier BV
Date: 06-2007
Publisher: EDP Sciences
Date: 2013
Publisher: American Physical Society (APS)
Date: 27-11-2018
Publisher: Cambridge University Press (CUP)
Date: 14-05-2020
DOI: 10.1017/QUA.2020.26
Abstract: Waterfall Bluff is a rock shelter in eastern Pondoland, South Africa, adjacent to a narrow continental shelf that limited coastline movements across glacial/interglacial cycles. The archaeological deposits are characterized by well-preserved stratigraphy, faunal, and botanical remains alongside abundant stone artifacts and other materials. A comprehensive dating protocol consisting of 5 optically stimulated luminescence ages and 51 accelerator mass spectrometry 14 C ages shows that the record of hunter-gatherer occupations at Waterfall Bluff persisted from the late Pleistocene to the Holocene, spanning the last glacial maximum and the transition from the Pleistocene to the Holocene. Here, we provide detailed descriptions about the sedimentary sequence, chronology, and characteristics of the archaeological deposits at Waterfall Bluff. Remains of marine mollusks and marine fish also show, for the first time, that coastal foraging was a component of some hunter-gatherer groups’ subsistence practices during glacial phases in the late Pleistocene. The presence of marine fish and shellfish further demonstrates that hunter-gatherers selectively targeted coastal resources from intertidal and estuarine habitats. Our results therefore underscore the idea that Pondoland's coastline remained a stable and predictable point on the landscape over the last glacial/interglacial transition being well positioned for hunter-gatherers to access resources from the nearby coastline, narrow continental shelf, and inland areas.
Publisher: Springer Science and Business Media LLC
Date: 06-04-2016
DOI: 10.1038/NATURE17196
Publisher: Babes-Bolyai University
Date: 20-04-2018
Publisher: Elsevier BV
Date: 07-2023
Publisher: Wiley
Date: 13-09-2019
DOI: 10.1002/ESP.4723
Publisher: Elsevier BV
Date: 10-2016
DOI: 10.1016/J.JENVRAD.2016.05.025
Abstract: We succeeded in obtaining the depth profile of
Location: Australia
No related grants have been discovered for The-Tien Nguyen.