698 research outputs found
Experimental investigation of open-ended microwave oven assisted encapsulation process
An open ended microwave oven is presented with improved uniform heating, heating rates and power conversion efficiency. This next generation oven produces more uniform EM fields in the evanescent region forming part of the heating area of the oven. These fields are vital for the rapid and uniform heating of various electromagnetically lossy materials. A fibre optic temperature sensor and an IR pyrometer are used to measure in situ and in real-time the temperature of the curing materials. An automatic computer controlled closed feedback loop measures the temperature in the curing material and drives the microwave components to
obtain predetermined curing temperature cycles for efficient curing. Uniform curing of the lossy encapsulants
is achieved with this oven with typical cure cycle of 270
seconds with a ramp rate of 1oC/s and a hold period of 2
minutes. Differential scanning calorimeter based measurement for the pulsed microwave based curing of
the polymer dielectric indicates a ~ 100% degree of cure
Ce and U speciation in wasteforms for thermal treatment of plutonium bearing wastes, probed by L3 edge XANES
X-ray absorption spectroscopy was applied to understand the speciation of elements relevant to the immobilisation and disposal of radioactive plutonium bearing wastes, utilizing Ce as a Pu surrogate. Ce L3 XANES (X-ray Absorption Near Edge Structure) characterisation of a crystallised glass material produced by cold crucible plasma vitrification, at demonstration scale, evidenced incorporation as Ce3+ within the glass phase, providing an important validation of laboratory scale studies. U and Ce L3 XANES investigation of brannerite ceramics, U0.9Ce0.1Ti2O6, synthesized under oxidizing, neutral and reducing conditions, established the charge compensation mechanism as incorporation of Ce3+ through formation of U5+ and/or U6+ In each of these examples, X-ray Absorption Spectroscopy has provided a pivotal understanding of element speciation in relation to the mechanism of incorporation within the host wasteform intended for geological disposal
Review of zirconolite crystal chemistry and aqueous durability
Zirconolite (CaZrTi2O7) has been identified as a candidate ceramic wasteform for the immobilisation and disposal of Pu inventories, for which there is no foreseen future use. Here, we provide an overview of relevant zirconolite solid solution chemistry with respect to Ce, U and Pu incorporation, alongside a summary of the available literature on zirconolite aqueous durability. The zirconolite phase may accommodate a wide variety of tri- and tetravalent actinide and rare-earth dopants through isovalent and heterovalent solid solution, e.g. CaZr1âxPuxTi2O7 or Ca1âxPuxZrTi2â2xFe2xO7. The progressive incorporation of actinides within the zirconolite-2M parent structure is accommodated through the formation of zirconolite polytypoids, such as zirconolite-4M or 3T, depending on the choice of substitution regime and processing route. A variety of standardised durability tests have demonstrated that the zirconolite phase exhibits exceptional chemical durability, with release rates of constituent elements typically <10â5 gmâ2·dâ1. Further work is required to understand the extent to which polytype formation and surrogate choice influence the dissolution behaviour of zirconolite wasteforms
Effects of Large CP violating phases on g_{\m}-2 in MSSM
Effects of CP violation on the supersymmetric electro-weak correction to the
anomalous magnetic moment of the muon are investigated with the most general
allowed set of CP violating phases in MSSM. The analysis includes contributions
from the chargino and the neutralino exchanges to the muon anomaly. The
supersymmetric contributions depend only on specific combinations of CP phases.
The independent set of such phases is classified. We analyse the effects of the
phases under the EDM constraints and show that large CP violating phases can
drastically affect the magnitude of the supersymmetric electro-weak
contribution to and may even affect its overall sign.Comment: 26 pages Latex file including 4 figure
Synthesis and characterisation of HIP Ca0.80Ce0.20ZrTi1.60Cr0.40O7 zirconolite and observations of the ceramicâcanister interface
A sample of zirconolite with nominal composition Ca0.80Ce0.20ZrTi1.60Cr0.40O7 was processed via Hot Isostatic Pressing (HIP), with a dwell temperature and pressure of 1320 °C/100 MPa maintained for 4 h. The produced wasteform was characterised by powder XRD, SEMâEDS, Ce L3 and Cr K-edge XANES. A significant portion of the Ce inventory did not fully partition within the zirconolite phase, instead remaining as CeO2 within the microstructure. Inspection of the stainless steelâceramic interface detailed the presence of an interaction region dominated by a Cr-rich oxide layer. No significant Cr or Fe migration was observed, although a greater concentration of perovskite was observed at the periphery, relative to the bulk ceramic matrix. The X-ray absorption features of Cr remained analogous with Cr3+ accommodation within TiO6 octahedra in the zirconolite matrix. The absorption edge of Ce was comprised of contributions from zirconolite-2M and unincorporated CeO2, with an average oxidation state of Ce3.9+. As zirconolite-2M accounted forâ>â92 wt% of the overall phase assemblage, it is clear that the dominant oxidation state of Ce in this phase was Ce4+
News from the Muon (g-2) Experiment at BNL
The magnetic moment anomaly a_mu = (g_mu - 2) / 2 of the positive muon has
been measured at the Brookhaven Alternating Gradient Synchrotron with an
uncertainty of 0.7 ppm. The new result, based on data taken in 2000, agrees
well with previous measurements. Standard Model evaluations currently differ
from the experimental result by 1.6 to 3.0 standard deviations.Comment: Talk presented at RADCOR - Loops and Legs 2002, Kloster Banz,
Germany, September 8-13 2002, to be published in Nuclear Physics B (Proc.
Suppl.); 5 pages, 3 figure
[Accepted Manuscript] Anthropometry and Malaria among Children in Niger: A Cross-Sectional Study.
The complex relationship between malnutrition and malaria affects morbidity and mortality in children younger than 5 years, particularly in parts of sub-Saharan Africa where these conditions occur together seasonally. Previous research on this relationship has been inconclusive. Here, we examine the association between anthropometric indicators and malaria infection in a population-based sample of children younger than 5 years in Niger. This cross-sectional study is a secondary analysis of a cluster-randomized trial comparing treatment strategies for trachoma in Niger. We included children aged 6-60 months residing in the 48 communities enrolled in the trial who completed anthropometric and malaria infection assessments at the final study visit. We evaluated the association between anthropometric indicators, including height-for-age z-score (HAZ) and weight-for-age z-score (WAZ) and indicators of malaria infection, including malaria parasitemia and clinical malaria. In May 2013, we collected data from 1,649 children. Of these, 780 (47.3%) were positive for malaria parasitemia and 401 (24.3%) had clinical malaria. In models of malaria parasitemia, the adjusted odds ratio (aOR) was 1.05 (95% confidence interval [CI]: 1.00-1.10) for HAZ and 1.07 (95% CI: 0.99, 1.15) for WAZ. In models of clinical malaria, the aOR was 1.07 (95% CI: 1.02-1.11) for HAZ and 1.09 (95% CI: 1.01-1.19) for WAZ. Overall, we did not find evidence of an association between most anthropometric indicators and malaria infection. Greater height may be associated with an increased risk of clinical malaria
Transverse Beam Spin Asymmetries in Forward-Angle Elastic Electron-Proton Scattering
We have measured the beam-normal single-spin asymmetry in elastic scattering
of transversely-polarized 3 GeV electrons from unpolarized protons at Q^2 =
0.15, 0.25 (GeV/c)^2. The results are inconsistent with calculations solely
using the elastic nucleon intermediate state, and generally agree with
calculations with significant inelastic hadronic intermediate state
contributions. A_n provides a direct probe of the imaginary component of the
2-gamma exchange amplitude, the complete description of which is important in
the interpretation of data from precision electron-scattering experiments.Comment: 5 pages, 3 figures, submitted to Physical Review Letters; shortened
to meet PRL length limit, clarified some text after referee's comment
Strange Quark Contributions to Parity-Violating Asymmetries in the Forward G0 Electron-Proton Scattering Experiment
We have measured parity-violating asymmetries in elastic electron-proton
scattering over the range of momentum transfers 0.12 < Q^2 < 1.0 GeV^2. These
asymmetries, arising from interference of the electromagnetic and neutral weak
interactions, are sensitive to strange quark contributions to the currents of
the proton. The measurements were made at JLab using a toroidal spectrometer to
detect the recoiling protons from a liquid hydrogen target. The results
indicate non-zero, Q^2 dependent, strange quark contributions and provide new
information beyond that obtained in previous experiments.Comment: 5 pages, 2 figure
The G0 Experiment: Apparatus for Parity-Violating Electron Scattering Measurements at Forward and Backward Angles
In the G0 experiment, performed at Jefferson Lab, the parity-violating
elastic scattering of electrons from protons and quasi-elastic scattering from
deuterons is measured in order to determine the neutral weak currents of the
nucleon. Asymmetries as small as 1 part per million in the scattering of a
polarized electron beam are determined using a dedicated apparatus. It consists
of specialized beam-monitoring and control systems, a cryogenic hydrogen (or
deuterium) target, and a superconducting, toroidal magnetic spectrometer
equipped with plastic scintillation and aerogel Cerenkov detectors, as well as
fast readout electronics for the measurement of individual events. The overall
design and performance of this experimental system is discussed.Comment: Submitted to Nuclear Instruments and Method
- âŠ