Jacqueline A. Johnson

Eu-activated fluorochlorozirconate glass-ceramic scintillators

Rare-earth-doped fluorochlorozirconate (FCZ) glass-ceramic materials have been developed as scintillators and their properties investigated as a function of dopant level. The paper presents the relative scintillation efficiency in comparison to single-crystal cadmium tungstate, the scintillation intensity as a function of x-ray intensity and x-ray energy, and the spatial resolution (modulation transfer function). Images obtained with the FCZ glass-ceramic scintillator and with cadmium tungstate are also presented. Comparison shows that the image quality obtained using the glass ceramic is close to that from cadmium tungstate. Therefore, the glass-ceramic scintillator could be used as an alternative material for image formation resulting from scintillation. Other inorganic scintillators such as single crystals or polycrystalline films have limitations in resolution or size, but the transparent glass-ceramic can be scaled to any shape or size with excellent resolution.

Tin oxidation state, depth profiles of Sn2+ and Sn4+ and oxygen diffusivity in float glass by Mössbauer spectroscopy

Abstract Mossbauer transmission spectra of tin in commercially produced soda-lime-silica float glass have been obtained at low temperatures. It was found that between 20% and 37% of the tin which had diffused into the lower surface of the ribbon during manufacture was in the Sn 4+ state. An estimate of the depth profiles for each oxidation state was obtained by measuring the Mossbauer spectra of samples after increasing thicknesses of the tin surface had been removed by polishing. These revealed that about 60% of the total Sn 2+ occurs in the first 3.5 μm, when the total tin penetration depth was 17 μm. Heat treatments were conducted to investigate the rate of oxidation of Sn 2+ to Sn 4+ in the glass. The diffusivity of oxygen into the glass was estimated to vary between 1.29 × 10 −18 m 2 s −1 at 500°C and 1.92 × 10 −16 m 2 s −1 at 730°C. Measurements of the decrease in recoil-free fraction with temperature enabled values for the Debye temperatures Θ D of Sn 2+ and Sn 4+ to be found to be 185 and 260 K respectively. These results show that the binding of tin at the surface of float glass is weaker than in bulk tin-containing glasses where Θ D was 200 K and 319 K.

Magnetic Resonance-Guided Laser Induced Thermal Therapy for Glioblastoma Multiforme: A Review

Magnetic resonance-guided laser induced thermotherapy (MRgLITT) has become an increasingly relevant therapy for tumor ablation due to its minimally invasive approach and broad applicability across many tissue types. The current state of the art applies laser irradiation via cooled optical fiber applicators in order to generate ablative heat and necrosis in tumor tissue. Magnetic resonance temperature imaging (MRTI) is used concurrently with this therapy to plan treatments and visualize tumor necrosis. Though application in neurosurgery remains in its infancy, MRgLITT has been found to be a promising therapy for many types of brain tumors. This review examines the current use of MRgLITT with regard to the special clinical challenge of glioblastoma multiforme and examines the potential applications of next-generation nanotherapy specific to the treatment of glioblastoma.

Atomic structure of solid and liquid polyethylene oxide

The structure of polyethylene oxide (PEO) was investigated by neutron scattering in both semicrystalline and liquid states. Deuterated samples were studied in addition to the protonated ones in order to avoid the large incoherent scattering of hydrogen and identify features in the pair correlation functions attributable to C–H pairs. Analysis of the deuterated sample gave additional information on the C–O and C–C pairs. The results are compared with molecular-dynamics simulations of liquid PEO.

Characterization of tin at the surface of float glass

Abstract Transmission Mossbauer spectroscopy (TMS) and conversion electron Mossbauer spectroscopy (CEMS) have been used to obtain spectra of 119Sn in three commercially produced soda–lime–silica float glasses. Measurements have been made of the f-factor of both tin oxidation states from a series of results at temperatures between 290 and 13 K. TM spectra yielded data on the whole tin layer, which extends to a depth of about 20 μm, while CEM spectra gave information on the near-surface region with a depth of about 2 μm. The isomer shift and quadrupole splitting of Sn4+ in the near-surface were higher than the shift and splitting measured for the whole region, and the Debye temperature, θD, was found to be significantly less in the surface than in the full depth containing tin, showing that it was less tightly bound. The shift, splitting and Debye temperature of Sn2+ remained the same throughout the glass surface within experimental errors. These results are discussed in terms of the conditions of the float process and differences in the coordination number of Sn4+.

Structural and optical investigations of Nd-doped fluorozirconate-based glass ceramics for enhanced upconverted fluorescence

We found enhanced upconverted fluorescence in Nd3+-doped fluorozirconate glasses which were additionally doped with chlorine ions. Upon annealing between 240 and 290°C, hexagonal phase BaCl2 nanocrystals between 20 and 180nm in diameter were formed in the glass. During the thermal processing, some of the Nd3+ ions enter the nanocrystals leading to additional splitting of the infrared fluorescence spectra and to increased upconverted fluorescence intensities. The optimum value was found for the 270°C sample where the upconverted fluorescence intensity is approximately a factor of 60 stronger than the one found for the as-made glass.

Transition metal ions in ternary sodium silicate glasses: a Mössbauer and neutron study

Abstract The structure of transition metal (TM) sodium silicate glasses of formulae (Fe2O3)x(Na2O)0.3(SiO2)0.7−x and (CoO)x(Na2O)0.3(SiO2)0.7−x where the nominal x=0, 0.05, 0.10, 0.15 and 0.20, have been studied using neutron diffraction and Mossbauer spectroscopy. The Mossbauer spectra of the iron-containing series show that both Fe3+ and Fe2+ are present, the majority being Fe3+. The isomer shifts show that the coordination number of Fe3+ is low, probably 4, and of Fe2+ somewhat higher though the measurement is less accurate. The neutron data show that both the iron and the cobalt are 4-coordinated with bond lengths of about 1.90 and 1.95 A, respectively with O–TM–O bond angles approaching 90°. The Fe–O bond length decreases and the O–O bond length increases with increasing Fe2O3 content. The first sharp diffraction peak (FSDP) is split on addition of iron and cobalt, showing intermediate-range order (IRO) with a larger repeat distance. The effective Debye temperatures for Fe2+ and Fe3+ are 268 and 312 K, respectively, showing the different Fe–O bond strengths of the two oxidation states arising from their different charges. The shift in the Mossbauer spectra with temperature was not that expected from the second order Doppler shift and thermal expansion showing an intrinsic isomer shift dependence on temperature. An attempt was made to relate this to the possible changes in hybridization of the iron with the concentration of Fe2O3.

Mossbauer spectra of tin in binary Si-Sn oxide glasses

The Mossbauer spectra of 119Sn in binary glasses of SnO and SiO2, in varying proportions of between 16.8 and 71.5 mol% SnO, have been obtained at 77 K. From these spectra the tin was found to be predominantly in the 2+ state. The isomer shift and the quadrupole splitting were both significantly greater than those in crystalline SnO and were found to decrease with increasing tin content, which also corresponds to decreasing molar volume. A second series of spectra of two of the samples was taken at temperatures between 10 and 300 K. These spectra show a decrease in shift with temperature which was the same for the two samples and which could only partly be accounted for by the second-order Doppler shift. The remainder was ascribed to the temperature dependence of the isomer shift. By using these data together with the measured expansivity and increase in density with tin content, it was possible to correct the isomer shift for the effects of the change in volume, and it was found that the volume-corrected isomer shift increased with increasing tin content. This showed that there was an increase in s-electron density at the tin nuclei, while the accompanying decrease in quadrupole splitting showed a decrease in the p-electron character, as expected for a decrease in covalency. From the decrease in absorption area with temperature the Debye temperature of tin was estimated to be ~190 K, which is slightly less than that of crystalline SnO, and decreased with increasing tin content. All the data suggest that the Sn-O bonds become progressively less covalent as more tin is added to SnO-SiO2 glasses, and possibly indicate a change from 4-fold to 6-fold co-ordination. A third series of spectra was obtained for the glass containing 40.9 mol% of SnO after a series of heat treatments. The spectra show changes in the oxidation state of the tin which depended upon the different conditions applied.

Insights into “near-frictionless carbon films”

A form of hydrogenated diamond-like-carbon, “near-frictionless carbon,” developed at Argonne National Laboratory has been studied by several spectroscopic techniques to determine the hydrogen content and carbon bonding within the film. The techniques used include hydrogen forward scattering, ultraviolet Raman spectroscopy, Fourier transform infrared spectroscopy, near-edge x-ray absorption fine structure, and fluctuation microscopy. These complementary techniques reveal the different types of carbon bonding, such as sp2 and sp3, the medium-range order in the film, and its composition.

Eu oxidation state in fluorozirconate-based glass ceramics

The influence of InF(3) doping and remelting on Eu-doped fluorozirconate-based glass ceramics was investigated using near-edge x-ray absorption and optical spectroscopy. It was found that the addition of InF(3) to the melt decreases the Eu(2+)Eu(3+) mole ratio, while remelting leads to a significant change in the Eu(2+)Eu(3+) ratio in favor of Eu(2+). Photoluminescence spectroscopy shows that additional annealing steps lead to the formation of BaCl(2) nanoparticles in the glass. In as-made glass ceramics containing InF(3), a phase transition of the nanoparticles from hexagonal to orthorhombic structure is observed. This phase transition is not observed in the remelted glasses studied here.