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Stereoselective synthesis of perdeuterated phytanic acid, its phospholipid derivatives and their formation into lipid model membranes for neutron reflectivity studies.
No full textWe describe a straightforward method, for synthesis of large scale (gram quantities) of highly deuterated phytanic acid from commercially available phytol while preserving the stereochemistry around the chiral centres. The subsequent synthesis of tail-deuterated analogues of the archeabacterial membrane lipids 1,2-di(3RS,7R,11R-phytanyl)-sn-glycero-3-phosphocholine (DPEPC) and 1,2-di(3RS,7R,11R-phytanoyl)-sn-glycero-3-phosphocholine (DPhyPC) from perdeuterated phytanic acid is also described. Both lipids were employed in construction of two different model membranes, namely Langmuir monolayers and a tethered bilayer membrane (TBM) on a solid substrate, characterised by pressure area isotherm and neutron reflectometry techniques. At 10 mN/m pressure the head-group thickness of both monolayers was similar while the thickness of the tail region was significantly larger for tail-deuterated DPhyPC, which was evident from a smaller area per molecule. At 20 mN/m the thickness of the head and tail regions in both lipids was comparable, yet the area per molecule of tail-deuterated DPhyPC was 10% smaller than tail-deuterated DPEPC. In the TBM bilayer model membrane, the thickness of the lipid tails in both inner and outer leaflets was 8.2 Å, giving a total of 16.4 Å. Deuteration enabled unambiguous determination of the relative proportion of the hydrogenous tether, phospholipid and subphase. © 2014, Elsevier Ireland Ltd
First accurate location of two proton sites in tourmaline: A single-crystal neutron diffraction study of oxy-dravite
No full textA single-crystal neutron diffraction study of oxy-dravite from Osarara (Narok district, Kenya) was performed. Intensity data were collected in Laue geometry at 10 K and anisotropic-structure refinement was undertaken. For the first time, two independent H sites were refined unambiguously for a mineral belonging to the tourmaline supergroup and located at 0.26, 0.13, 0.38 (labelled as H3, site occupancy ~98%) and at 0, 0, 0.9 (labelled as H1, site occupancy ~25%). The H-bonding scheme can thus be defined as follows: (1) the O at the O3 site acts as a ‘donor’ and the O at the O5 site as ‘acceptor’, the refined O3–H3 bond distance is 0.972(2) Å (and 0.9946 Å corrected for “riding motion”), H3⋯O5 = 2.263(2) Å, O3⋯O5 = 3.179(1) Å and O3–H3⋯O5 = 156.6(1)°; (2) the oxygen at the O1 site acts as a ‘donor’ and the O atoms at O4 and O5 as ‘acceptors’, the refined O1–H1 bond distance is 0.958(8) Å (and 0.9833 Å corrected for “riding motion”), H1⋯O4 = 2.858(6) Å, O1⋯O4 = 3.378(1) Å and O1–H1⋯O4 = 115.12(1)°, whereas H1⋯O5 = 2.886(6) Å, O1⋯O5 = 3.444(1) Å and O1–H1⋯O5 = 118.23(1)°. A further test refinement was performed with the H1 site out of the three-fold axis (at 0.02, 0.01, 0.90); this leads to O1–H1 = 0.995(8) Å (and 1.0112 Å corrected for “riding motion”), H1⋯O4 = 2.747(6) Å and O1–H1⋯O4 = 121.7(4)°, whereas H1⋯O5 = 2.654(9) Å and O1–H1⋯O5 = 136.5(6)°. Bond-valence analysis shows that the H-bonding strength involving O3 is stronger than that involving O1: ~0.11 and <0.05 valence units, respectively. The refined angle between the O3–H3 vector and [0001] is 3.40(9)°. Such a small angle is in line with a pleochroic scheme for the OH-stretching absorption bands measured by infrared spectroscopy. © The Mineralogical Society of Great Britain & Ireland
Crystal structures of orthorhombic, hexagonal, and cubic compounds of the Sm(x)Yb(2−x)TiO5 series
No full textA series of single phase compounds with nominal stoichiometry Sm(x)Yb(2−x)TiO5 (x=2, 1.4, 1, 0.6, and 0) have been successfully fabricated to generate a range of crystal structures covering the most common polymorphs previously discovered in the Ln2TiO5 series (Ln=lanthanides and yttrium). Four of the five samples have not been previously fabricated in bulk, single phase form so their crystal structures are refined and detailed using powder synchrotron and single crystal x-ray diffraction, neutron diffraction and transmission electron microscopy. Based on the phase information from diffraction data, there are four crystal structure types in this series; orthorhombic Pnma, hexagonal P63/mmc, cubic (pyrochlore-like) Fd-3m and cubic (fluorite-like) Fm-3m. The cubic materials show modulated structures with variation between long and short range ordering and the variety of diffraction techniques were used to describe these complex crystal structure types. © 2014, Elsevier Inc
Evaluate transport processes in MERRA driven chemical transport models using updated 222Rn emission inventories and global observations
Get PDFConvective and synoptic processes play a major role in determining the transport and distribution of trace gases and aerosols in the troposphere. The representation of these processes in global models (at ~100-1000 km horizontal resolution) is challenging, because convection is a sub-grid process and needs to be parameterized, while synoptic processes are close to the grid scale. Depending on the parameterization schemes used in climate models, the role of convection in transporting trace gases and aerosols may vary from model to model. 222Rn is a chemically inert and radioactive gas constantly emitted from soil and has a half-life (3.8 days) comparable to synoptic timescale, which makes it an effective tracer for convective and synoptic transport. In this study, we evaluate the convective and synoptic transport in two chemical transport models (GMI and GEOS-Chem), both driven by the NASA’s MERRA reanalysis. Considering the uncertainties in 222Rn emissions, we incorporate two more recent scenarios with regionally varying 222Rn emissions into GEOS-Chem/MERRA and compare the simulation results with those using the relatively uniform 222Rn emissions in the standard model. We evaluate the global distribution and seasonality of 222Rn concentrations simulated by the two models against an extended collection of 222Rn observations from 1970s to 2010s. The intercomparison will improve our understanding of the spatial variability in global 222Rn emissions, including the suspected excessive 222Rn emissions in East Asia, and provide useful feedbacks on 222Rn emission models. We will assess 222Rn vertical distributions at different latitudes in the models using observations at surface sites and in the upper troposphere and lower stratosphere. Results will be compared with previous models driven by other meteorological fields (e.g., fvGCM and GEOS4). Since the decay of 222Rn is the source of 210Pb, a useful radionuclide tracer attached to submicron aerosols, improved understanding of emissions and transport of 222Rn will provide insights into the transport, distribution, and wet deposition of 210Pb aerosols
Proceedings of the 12th European Conference on Accelerators in Applied Research and Technology (ECAART12) available at https://www.sciencedirect.com/journal/nuclear-instruments-and-methods-in-physics-research-section-b-beam-interactions-with-materials-and-atoms/vol/406/part/PA
No full textThe Centre for Accelerator Science at ANSTO operates four tandem accelerator systems for Accelerator Mass Spectrometry (AMS) and Ion Beam Analysis (IBA). The latest addition to the fleet is SIRIUS, a 6 MV combined IBA and AMS system. Following initial ion beam testing, conditioning and debugging software and hardware, SIRIUS is now commissioned. Details of the instrument design and performance data for 10Be, 26Al and 36Cl are presented
Analysis of hot particle characteristics affecting environmental fate and interaction with living organisms
No full textThe 2nd International Conference on the Sources, Effects and Risks of Ionizing Radiation (SERIR-2) and the 14th Biennial Conference of the South Pacific Environmental Radioactivity Association (SPERA-2016) and will be held in Bali, Indonesia 5-9 September 2016.
The South Pacific Environmental Radioactivity Association (SPERA), in conjunction with the Indonesian National Nuclear Energy Agency (BATAN) and the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) made the decision to jointly hold these conferences in one week at the same venue to avoid topical overlap and to strengthen regional participation at both events.
SERIR2 will be a 1-day conference (5 September) and deals with the efforts to enhance data collection and disseminate scientific findings related to the issues of sources, effects and risks of the ionizing radiation, as well as to seek ways of communicating with stakeholders (scientific communities, regulatory authorities and general public) on those issues.
The 14th Biennial Conference of the South Pacific Environmental Radioactivity Association (SPERA), to be held 6-9 September, provides a platform for discussion and debate among scientists on the occurrence, behaviour, impact and measurement of radioactive species present in the environment through natural processes, or resulting from human activities. This international conference facilitates knowledge sharing on environmental radioactivity and related topics of local and global significance.
The joint conference will be held 5-9 September 2016, with a welcome reception on 4 September, at the Sanur Paradise Plaza Hotel in Bali.
The joint conference will include a one-day workshop on the 6 September on topic(s) to be decided
Recycling of Pleistocene valley fills dominates 125 ka of sediment flux, upper Indus River
Get PDFRivers draining the semiarid Transhimalayan Ranges along the western Tibetan Plateau margin underwent alternating
phases of massive valley infill and incision in Pleistocene times. The imprints of these cut-and-fill cycles on
long-term sediment fluxes have remained largely elusive. We investigate the timing and geomorphic consequences
of headward incision of the Zanskar River, which taps the vast More Plains valley fill that currently impedes
drainage of the endorheic high-altitude basins of Tso Kar and Tso Moriri. In situ 10Be exposure dating and topographic
analyses indicate that a phase of valley infill gave way to net dissection of the >250-m thick sedimentary
stacks ∼125 ka ago, i.e. during the last interglacial (MIS 5e). Rivers eroded >14.7 km3 of sediment from the Zanskar
headwaters since then, fashioning specific sediment yields that surpass 10Be-derived denudation rates from
neighbouring catchments by factors of two to ten. We conclude that recycling of Pleistocene valley fills has provided
Transhimalayan headwater rivers with more sediment than bedrock denudation, at least since the beginning
of the last glacial cycle. This protracted liberation of sediment stored in thick valley fills could bias rate estimates
of current sediment loads and long-term bedrock denudation
Spatial pattern of denudation in a lithologically controlled sub-tropical flat landscape: Insights from the Kimberley region, NW Australia
Get PDFThe Kimberley region, northwest Australia, is well known for its expansive and diverse collection of prehistorical
aboriginal rock art that potentially dates back to 40,000 years ago. The region is characterized by a tropical, semiarid
climate with a monsoonal rainfall distribution and a flat landscape interrupted by massive sandstone mesas and
deeply incised bedrock river gorges. In order to constrain the chronology of the rock art it is necessary to quantify
the spatial and temporal dimensions of landscape evolution.
We report cosmogenic 10Be and 26Al concentrations in modern fluvial sediment collected from 27 catchments with
areas spanning several orders of magnitude (13.6 – 13,900 km2
). All catchments are characterized by a very low
topographic gradient (average basin slopes < 3◦
) and subdued local relief of at most 200m. Assuming negligible
sediment storage times and rapid sediment transport driven by the annual monsoonal washout, we calculate 10Be
based catchment-wide denudation rates ranging between 1.87 ± 0.23 and 9.48 ± 1.05 m.Myr−1
. These low rates
are among the slowest recorded in the world, despite the strong climatic seasonality of the region. Our measured
denudation rates exhibit a strong correlation with topographic gradient, which in the overall flat landscapes of the
Kimberley, is controlled by the prevailing sandstone bedrock lithology and the presence of numerous escarpments
adjacent to the river channels. We present a modelling approach that makes use of the 26Al/10Be ratio in the fluvial
sediments as a source tracer (ie escarpment cliffs, river channels, plateau bedrocks), and use this to explore the
control and retreat rate of the eroding escarpment cliffs in order to provide information on the spatial distribution
of denudation in the landscape. © Author(s) 2016. CC Attribution 3.0 License
Residual stresses in a welded zircaloy cold neutron source containment vessel
No full textZirconium alloys are widely used in the nuclear industry because of their relative high strength, neutron transparency, resistance to high neutron-irradiation environment and corrosion resistance. One application for Zirconium alloy Zr-2.5Nb is the vacuum confinement vessel utilised in the cold neutron source of the OPAL research reactor at ANSTO. Having a total length of more the 3 meters, it is made of two sections joined using electron beam welding. The weld and the nearby regions are critical for the performance and integrity of the component and therefore understanding of the residual stresses development within the weld is important in connection to (i) evolution of fine dual phase α/b microstructure and crystallographic texture (ii) and stress-related radiation induced phenomena, such as grain growth, creep and sub-critical crack growth by delayed hydride cracking. The stresses were measured in and around an electron beam weld produced during the development of this component of the OPAL Cold Neutron Source. The effects of a large grain size in the weld were reduced by taking advantage of rotational symmetry and rotating the sample to increase the swept volume. Due to the heat-treatment after welding, the stresses were very low, less than 10% of the yield strength of the material, in both the hoop and axial directions. As a result of phase transformation effects during the welding process the final stresses are compressive in the weld, which reduces the likelihood of fracture or of hydride formation in this region. The highest stresses are in the parent material adjacent to the weld where the toughness is expected to be higher than in the weld material
Neutron diffraction characterization of C–H···Li interactions in a lithium aluminate polymer
No full textThe reaction of AlMe3 with tBuLi in the presence of trimethylacetonitrile affords the bimetallic complex [tBu(Me)Al(μ-Me)2Li·NC(tBu)]∞ (1). Pseudotetrahedral Al centers form by the nucelophilic addition of tBuLi to AlMe3.The alkali-metal center is stabilized through coordination of the unreacted nitrile and polymer formation via the construction of Al(μ-Me)nLi (n = 1, 2) motifs. Neutron diffraction evidences agostic interactions in the bridging methyl group to give further stabilization. There is only one previous report of a neutron structure of a lithium aluminate compound. This work therefore offers an important structural example of agostic interactions and the precise nature of Al(μ-Me)2Li bridging.© 2014, American Chemical Society