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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Unraveling the individual influences of supports and ionic liquid coatings on the catalytic properties of supported iridium complexes and iridium clusters

In this work, supported iridium complexes were synthesized by the reaction of Ir(CO) 2 (acac) (acac = acetylacetonato) with SiO 2 , γ-Al 2 O 3 , and MgO. Extended X-ray absorption fine structure (EXAFS) and infrared (IR) spectra demonstrate that the iridium was present as atomically dispersed species anchored to each support. The samples were treated in flowing H 2 at 673 K to form supported iridium clusters. EXAFS spectra and high-angle annular dark-field scanning transmission electron microscopy images demonstrate that the average diameter of the iridium clusters on each support was approximately 1.2 nm. Furthermore, the catalysts before and after cluster formation were coated with each of a family of 1,3-dialkylimidazolium ionic liquids (ILs) having varying electron-donor tendencies probed by their υ(C2H) frequencies determined by IR spectroscopy. The coated and uncoated samples were tested as catalysts for partial hydrogenation of 1,3-butadiene in a flow reactor at 333 K, with turnover frequencies determined from differential conversions. The individual influences of the IL coatings and supports on the catalyst performance were found to depend strongly on whether the iridium was site-isolated complexes or present in clusters. The IL coatings as ligands exerted dominant effects on the clusters as catalysts, whereas the supports exerted dominant effects on the isolated iridium atoms. The results indicate how to tune the effects of metal nuclearity, IL coatings, and supports on the electronic environments and catalytic properties of the metals.

1,3-Butadiene hydrogenation↗
DOE OSTI2020

Rates of levoglucosanol hydrogenolysis over Brønsted and Lewis acid sites on platinum silica-alumina catalysts synthesized by atomic layer deposition

Nanoscale coatings of AlO x were deposited onto SiO 2 using atomic layer deposition (ALD) to synthesize amorphous silica-alumina (SiAl) catalysts, and these catalysts were investigated for levoglucosanol (Lgol) hydrogenolysis. With decreasing Al 2 O 3 loading, the ratio of Brønsted to Lewis acid sites, measured by NH 3 -TPD and pyridine-FTIR, systematically increases, while the Al coordination, measured by solid state 27 Al NMR, decreases. These structural changes correspond to an increasing mass-normalized rate of Lgol hydrogenolysis. We model the mass-normalized reaction rate as the sum of independent contributions from Brønsted and Lewis sites, showing that Brønsted acid sites on ALD-AlO x /SiO 2 catalysts have a 6-times higher turnover frequency (TOF) than Lewis acid sites on these catalysts. Additionally, Lewis acid sites on ALD-AlO x /SiO 2 catalysts (potentially related to Al(V) species) have a 4-times higher TOF than Lewis acid sites on bulk γ-Al 2 O 3 . The overall mass-normalized reactivity of ALD-AlO x /SiO 2 catalysts is due to Lewis acid sites at the highest Al 2 O 3 loading, while it is predominantly due to Brønsted acid sites at the lowest Al 2 O 3 loadings. In conclusion, this work provides a new approach to synthesize amorphous SiAls with tunable Brønsted/Lewis acid site ratio and reveals differences in the reactivity of Brønsted and Lewis acid sites on these materials.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Identifying higher oxygenate synthesis sites in Cu catalysts promoted and stabilized by atomic layer deposited Fe 2 O 3

The conversion of syngas to higher oxygenates is an important step in the pathway towards the long-term sustainable production of fuels and chemicals. Mixed Cu/Fe catalysts combine metals with different CO activation characteristics, a property that makes them promising candidates for higher oxygenate production. However, Cu/Fe catalysts suffer from instability due to sintering and phase separation, and the active sites for higher oxygenate formation on these materials are not well understood. In this work, we use atomic layer deposition (ALD) to modify silica-supported Cu nanoparticles with monolayer precise amounts of Fe 2 O 3 and study the effects on catalyst structure, reactivity, and stability. We demonstrate that the Fe 2 O 3 ALD process is inherently selective towards deposition on the SiO 2 surface versus the Cu nanoparticles. As a result, a sufficiently thick Fe 2 O 3 layer surrounding the Cu nanoparticles acts as a barrier against Cu migration, preventing catalyst deactivation through sintering without covering the Cu. In syngas conversion reactions, we find that higher oxygenate selectivity increases with Fe 2 O 3 loading at low and intermediate ALD cycle numbers. Furthermore, using in situ X-ray absorption spectroscopy, we demonstrate that the Fe near the Cu nanoparticles is reduced to a metallic state under reaction conditions. From these measurements, we identify these metallic Cu/Fe interfaces as the active sites for higher oxygenate formation, which are most abundant at intermediate Fe 2 O 3 ALD cycle numbers. As the Fe 2 O 3 loading increases, higher oxygenate selectivity falls, resulting from encapsulation of the Cu nanoparticles by thick Fe 2 O 3 layers. Overall, the results demonstrate how thickness-controlled ALD Fe 2 O 3 can be used as both a promoter and stabilizer of Cu-based higher oxygenate synthesis catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Supported molybdenum oxides for the aldol condensation reaction of acetaldehyde

The (retro-)aldol condensation reaction is an important chemical transformation in the upgrading of biomass-derived compounds into fuels and valuable specialty chemicals. In this study, we found that supported molybdenum oxide (MoO x ) catalysts were active and selective for the aldol condensation of acetaldehyde to crotonaldehyde under steady-state reactor conditions. Through a combination of transmission electron microscopy (TEM), ultraviolet–visible (UV–VIS) diffuse reflectance spectroscopy, Fourier transform infrared (FTIR) spectroscopy of adsorbed pyridine, and steady-state reactor testing, we determined that highly dispersed MoO x has a strong interaction with a γ-Al 2 O 3 support resulting in optimal catalyst performance at low weight loadings. In contrast, MoO x particles supported on SiO 2 have a weaker interaction with the support, resulting in a monotonic relationship between Mo loading and aldol condensation activity. The Lewis acid site density and strength are important parameters for predicting aldol condensation activity across all samples. The concentration of weak acid sites had a poor correlation with aldol condensation activity, most likely because these sites are too weak to activate acetaldehyde for the reaction. Medium and strong acid sites both had good correlations to aldol condensation activity. Results from X-ray absorption near edge structure (XANES) and acetaldehyde temperature programmed desorption (TPD) indicated that partially reduced MoO x was more active for aldol condensation, but pretreatment in reducing or oxidizing environments had no significant effect on steady-state catalytic activity. Finally, characterization of spent catalyst samples through temperature programmed oxidation (TPO) and thermogravimetric analysis (TGA) revealed that catalysts with high densities of strong acid sites tended to form more carbonaceous deposits on the surface over the course of the reaction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Topological origin of phase separation in hydrated gels

Depending on their composition, hydrated gels can be homogeneous or phase-separated, which, in turn, affects their dynamical and mechanical properties. However, the nature of the structural features, if any, that govern the propensity for a given gel to phase-separate remains largely unknown. Here, we argue that the propensity for hydrated gels to phase-separate is topological in nature. We employ reactive molecular dynamics simulations to model the early-age precipitation of calcium–alumino–silicate–hydrate (Csingle bondAsingle bondSsingle bondH) gels with varying compositions, i.e., (CaO) 1.7 (Al 2 O 3 ) x (SiO 2 ) 1 – x (H 2 O) 3.7 + x . By adopting topological constraint theory, we investigate the structural origin of phase separation in hydrated gels. We report the existence of a homogeneous-to-phase-separated transition, wherein Si-rich (x ≤ 0.10) Csingle bondAsingle bondSsingle bondH gels are homogeneous, whereas Al-rich (x > 0.10) Csingle bondAsingle bondSsingle bondH gels tend to phase-separate. Furthermore, we demonstrate that this transition is correlated to a topological flexible-to-rigid transition within the atomic network. Finally, we reveal that the propensity for topologically-overconstrained gels to phase-separate arises from the existence of some internal stress within their atomic network, which acts as an energy penalty that drives phase separation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Conversion of ethanol to 1,3–butadiene over Ag–ZrO 2 /SiO 2 catalysts: The role of surface interfaces

A series of Ag–ZrO 2 /SiO 2 catalysts with different metal–support interfaces were synthesized in an effort to elucidate the roles of specific interfaces in controlling the ethanol to 1,3–butadiene conversion and selectivity. According to the results of detailed characterizations (e.g. CO/pyridine–DRIFTS, XPS, TEM, NH 3 –TPD, and 1 H MAS NMR), it was found that the Ag–O–Si interfaces significantly enhanced the dehydrogenation of ethanol while the presence of ZrO 2 improved the interaction between Ag and ZrO 2 /SiO 2 , creating more Ag δ+ active sites. In this research, the high dispersion of ZrO 2 on SiO 2 generated abundant Zr–O–Si interfaces with medium and weak Lewis acidity, promoting the condensation of acetaldehyde to crotonaldehyde. These Zr–O–Si interfaces in close interaction with Ag δ+ species played a critical role in the enhanced H transfer during the MPV reduction of crotonaldehyde to crotyl alcohol. The synergies among the interfaces resulted in retarded ethanol dehydration reactivity, balanced ethanol dehydrogenation and condensation reactions, and a subsequent high 1,3–butadiene yield.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Oxidation of ultrahigh temperature ceramics: kinetics, mechanisms, and applications

Materials capable of oxidizing in a protective manner at ultrahigh (>1700 °C) temperatures are needed to push beyond this barrier defined by SiC. Although possessing attractive mechanical properties and oxidation resistance, SiC-based materials are ultimately temperature limited by the melting point of SiO 2 . The vast array of ultra-high and high temperature ceramic literature indicates the majority of these materials, like borides, carbides, MAX-phases, and high-entropy ceramics, fall woefully short regarding oxidation resistance. However, for specific applications, like low-orbit aeropropulsion, high ballistics coefficient atmospheric re-entry, and hypersonic cruise, there are a few promising materials. Here, oxidation criteria are gathered to build application specific heuristics and are then applied to a multitude of ultra-high temperature ceramics to gauge material efficacy. Discussion of oxidation kinetics, mechanisms and reaction products is offered for each material, identifying strengths, weaknesses, and the remaining gaps in our knowledge.

36 MATERIALS SCIENCE↗
DOE OSTI2022

In-situ TEM study of Kr ion irradiation tolerance of SiFeOC nanocomposite

Here, in this work, ion irradiation of polymer derived SiFeOC nanocomposite was carried out using 1.2 MeV Kr ions at room temperature and 600°C. The starting composite was composed of Fe 3 Si, SiC, SiOC, SiO 2 , and graphitic C. In-situ TEM investigations show uniform distribution of nano-crystalline Fe 3 Si and SiC phases in the amorphous SiOC matrix. During ion irradiation, the SiOC bulk microstructure and interfaces between Fe 3 Si or SiC crystallites and the SiOC matrix remain defect-free and demonstrate outstanding ion irradiation resistance. At room temperature, the crystalline domains are stable up to 2 dpa. At 600°C, Fe 3 Si crystallites are more stable than SiC; SiC crystallites are stable up to 4 dpa while the Fe 3 Si crystallites are stable up to 10 dpa. These crystallites also coalescence and amorphize simultaneously during ion irradiation. The exceptional tolerance to defect formation and irradiation of the SiFeOC nanocomposite provides important guidance to developing irradiation resistant fuels for advanced gas cooled reactors.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Influence of temperature, oxygen partial pressure, and microstructure on the high-temperature oxidation behavior of the SiC Layer of TRISO particles

Tristructural isotropic (TRISO)-coated fuel particles are designed for use in high-temperature gas-cooled nuclear reactors, featuring a structural SiC layer that may be exposed to oxygen-rich environments over 1000 °C. Surrogate TRISO particles were tested in 0.2–20 kPa O 2 atmospheres to observe the differences in oxidation behavior. Oxide growth mechanisms remained consistent from 1200–1600 °C for each P O$_2$ , with activation energies of 228 ± 7 kJ/mol for 20 kPa O 2 and 188 ± 8 kJ/mol for 0.2 kPa O 2 . At 1600 °C, kinetic analysis revealed a change in oxide growth mechanisms between 0.2 and 6 kPa O2. In 0.2 kPa O 2 , oxidation produced raised oxide nodules on pockets with nanocrystalline SiC. Oxidation mechanisms were determined using Atom probe tomography. Active SiC oxidation occurred in C-rich grain boundaries with low P O$_2$ , leading to SiO 2 buildup in porous nodules. Here, this phenomenon was not observed at any temperature in 20 kPa O 2 environments.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2021

Solid phase characterization and transformation of illite mineral with gas-phase ammonia treatment

In situ remediation applications of ammonia (NH 3 ) gas have potential for sequestration of subsurface contamination. Ammonia gas injections initially increase the pore water pH leading to mineral dissolution followed by formation of secondary precipitates as the pH is neutralized. However, there is a lack of understanding of fundamental alteration processes due to NH 3 treatment. In these batch studies, phyllosilicate minerals (illite and montmorillonite) were exposed to NH 3 gas with subsequent aeration to simulate in situ remediation. Following treatments, solids were characterized using a variety of techniques, including X-ray diffraction, N 2 adsorption-desorption analysis for surface area, Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR), and microscopy methods to investigate physicochemical transformations. The results of this study indicate that, at high pH, the clays are altered as observed by differences in morphology and particle size via microscopy. However, the two clays interact differently with NH 3 . While montmorillonite interlayers collapsed due to intercalation, illite layers were unaffected as confirmed by FTIR analysis. Further, structural changes in silicate ([SiO 4 ] n- ) and aluminol (Al-OH) groups were identified by NMR and FTIR. This research showed that mineral alteration processes occur during and after NH 3 gas treatment which may be used to remove radionuclides from the aqueous phase through sorption, co-precipitation, and coating with secondary phyllosilicate alteration products.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

High-resolution laser-induced fluorescence spectroscopy of 28 Si 16 O + and 29 Si 16 O + in a cryogenic buffer-gas cell

Here, the electronic, laser-induced fluorescence spectrum of the B 2 Σ + ← X 2 Σ + transition in 28 Si 16 O + and 29 Si 16 O + has been recorded in a cryogenic buffer gas cell at K. Molecular constants are extracted for both 28 Si 16 O + and 29 Si 16 O + , including the Fermi contact hyperfine constant for both the B and X states of 29 Si 16 O + , and used in a discussion of the suitability of SiO in future quantum information experiments.

47 OTHER INSTRUMENTATION↗
DOE OSTI2023

The C 2 H 4 O isomers in the oxidation of ethylene

A combined rotational spectroscopy, thermochemistry, and kinetic modeling study explores the mechanism of acetaldehyde (ethanal), vinyl alcohol (ethenol), and ethylene oxide (oxirane) formation in the oxidation of ethylene (ethene). Multiplexed quantitative detection of oxidation intermediates and products exiting a SiO 2 / SiC microreactor at 1700 K is demonstrated with the BrightSpec W-band chirped-pulse Fourier transform millimeter-wave spectrometer. The broadband rotational spectrum contains transitions of formaldehyde (CH 2 O), methoxy (CH 3 O), methanol (CH 3 OH), ketene (CH 2 CO), acetaldehyde (CH 3 CHO), syn-vinyl alcohol (syn- CH 2 CHOH), anti-vinyl alcohol (anti-CH 2 CHOH), oxirane (c-CH 2 OCH 2 ), propyne (CH 3 CCH), and syn-propanal (syn-CH 3 CH 2 CHO). We focus on the three C 2 H 4 O species and deduce their concentration ratio [CH 3 CHO]:[CH 2 CHOH]:[c-CH 2 OCH 2 ] = 1:0.7(2):0.06(2) by comparing the observed line intensities to those simulated with the PGOPHER software. Detailed thermochemistry of the C 2 H 4 O isomers and conformers is provided by Active Thermochemical Tables. The observed excess concentrations of vinyl alcohol and oxirane relative to the more stable acetaldehyde compared to the equilibrium ratio at 1700 K (1:0.087:0.000024), point to direct chemical pathways to these higher energy isomers. The mechanism for the formation of the three C 2 H 4 O isomers is analyzed using a 0-D homogenous reactor kinetics simulation for ethylene oxidation. The ratios of the C 2 H 4 O isomers concentrations predicted by the kinetic model are compared to the experimental values.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

A comparative study of the effectiveness of empirical potentials for molecular dynamics simulations of borosilicate glasses

Despite their practical importance, atomistic modeling of B 2 O 3 containing glasses have been challenging due to the lack of reliable empirical potentials. Fortunately, a few recent developments have shown promises to simulate these glasses where the boron coordination has complex and non-linear dependence on glass composition. This work aims to provide an evaluation of the effectiveness of three recently developed potentials by a systematic study of a series (~20) of sodium borosilicate glasses with constant K (ratio of [SiO 2 ]/[B 2 O 3 ]) =2 and varying R (ratio of [Na 2 O]/[B 2 O 3 ] ranging from 0.1 to 4) values and several sodium boroaluminosilicate glasses. A comparative assessment was established on the basis of the short- and medium-range structure features, such as boron N 4 values, total correlation functions, bond angle distribution, oxygen speciation, and mechanical properties using experimental or well-established models as criteria. Furthermore, this work provides insights on the choices of empirical potentials for MD simulations of borosilicate glasses and gives directions of future potential development and refining.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2020

Anomalously strong viscosity behavior in mixed oxy-sulfide Na 4 P 2 S 7-x O x invert glasses

In this paper, the first observations have been made of anomalously strong viscosity behavior and correspondingly strong bulk glass formation and resistance to crystallization in a melt quenched (MQ) prepared series of invert, modifier content greater than the glass former content, mixed oxy-sulfide Na 4 P 2 S 7-x O x , 0 ≤ x ≤ 5, (NaPSO) glasses. We find that these glasses even with 67 mole % modifier, Na 2 S, and only 33 mole% glass former P 2 S 5-x O x , exhibit a calorimetric fragility index, m cal , as small as 29 compared to typical values of ~ 60 to 80 for alkali silicate glasses with > 50 mole% SiO 2 and the theoretical minimum m cal of ~ 15. The m cal values were converted to kinetic viscosity fragility, m vis , values and used with the measured glass transition temperatures, T g s, to produce viscosity curves for the glasses using the Mauro-Yue-Ellison-Gupta-Allan (MYEGA) model. The viscosity of the glass with a minimum m cal value of x = 2.5 was then shown to exhibit a viscosity that was as strong as, and for some compositions stronger than, the viscosity of alkali aluminosilicate glasses which have three dimensional network structures compared to the one dimensional chain structures observed in these MOS invert glasses. Consistent with these small values of fragility indices and therefore predicted higher viscosity above the glass transition temperature, T g , in the supercooled liquid regime, these glasses are also particularly resistant to crystallization. For example, the x = 2.5 glass composition exhibits a crystallization temperature, T C , more than 150K above its T g . We find that the calorimetric fragility of these glasses varies systematically with the extent of network forming bridging oxygens (BOs) in the glasses. The structural change caused by incrementally replacing sulfur with oxygen has been found to have consistent, large effects on the thermal properties.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Nanoscopic structure of borosilicate glass with additives for nuclear waste vitrification

In this report we investigated the nanoscopic structure of borosilicate glasses as a host for high-level radioactive liquid waste (HLLW) in the presence of the additives Na 2 O and CaO/ZnO with and without Li 2 O. These additives have been used to lower the glass melting point, suppress the macroscopic phase separation, and increase the chemical durability of glasses. Small-angle neutron scattering was used to elucidate the effect of the additives on the nanoscopic structure along with macro- and atomic-scale observations obtained using neutron imaging and X-ray diffraction, respectively. The borosilicate glass made without Na 2 O formed a microphase-separated structure of SiO 2 - and B 2 O 3 -rich domains approximately 100 nm in size, and the material was homogeneous at length scales up to millimeters. With the addition of increasing amounts of Na 2 O, the domain spacing decreased. Introducing CaO/ZnO additives induced inhomogeneities in the glass, such as void structures several nanometers in size, although the inhomogeneity was suppressed by the coaddition of Li 2 O. These results provide insights into the performance of host glasses for HLLW vitrification. Incorporating HLLW into glasses is likely to cause changes in the nanoscopic structure of host glasses similar to those revealed here.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2022

In-situ investigation of the vibrational properties of H 2 O CO 2 -bearing and dry K-rich basaltic glasses at high pressure by mid infrared spectroscopy

Here, the vibrational properties of CO 2 –H 2 O-bearing and dry synthetic K-rich basaltic glasses were investigated at room temperature and pressures between 0.0001–5.5 GPa using the diamond anvil cell combined with in situ reflectance and transmittance Fourier Transform infrared micro-spectroscopy. The absorption coefficient a(v) calculated from the Kramers-Kronig relation shows that glasses are dominated by the Q 2 aluminosilicate unit followed by Q 1 , Q 3 . The variation in Q n concentration upon compression suggests that glasses undergo polymerization from ambient pressure to 2 GPa followed by less marked structural changes up to 4 GPa, above which the structure is further polymerized. Once decompressed, glasses retained a polymerized structure. Our results show that 1.03 wt% CO 2 -1.42 wt% H 2 O in a glass with 3.10 wt% K 2 O and 46.77 wt% SiO 2 prevent the formation of fully polymerized connections when cold-compressed. Our results can be used to explain the effect of volatiles and alkali on the rheology of natural basaltic magmas.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Study of beyond nearest-neighbor environment and intermediate-range order in a sodium aluminosilicate geopolymer using Reverse Monte Carlo modeling

A large scale three-dimensional structural model of a geopolymer with an approximate composition of NaAlSi 2 O 6 .5.5H 2 O obtained by Reverse Monte Carlo (RMC) modeling based on experimental high-energy x-ray diffraction is presented for the first time in order to obtain information regarding beyond nearest-neighbor environment and intermediate-range order (IRO). RMC model exhibits a three-dimensional network consisting of randomly cross-linked AlO 4 and SiO 4 tetrahedral units with uniformly distributed Na atoms and H 2 O molecules. The bond angle distributions, i.e. T-O-T, O-T-O and Na-O-Na angles, are somewhat distorted with lower values compared to analogous crystal systems. The origin of the first peak in the structure factor indicating IRO is investigated using the partial structure factors; Na-Na, Si-Na, Al-Si, O-H, and H-H atom pairs are found to be the main contributors. Ring size distribution analysis demonstrates that the structure mainly involves 6-, 7- and 8-membered rings. Finally, the coherence length of these IRO characteristics is ~10.3 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Enhanced backscatter and unsaturated blue wavelength shifts in F-doped fused silica optical fibers exposed to extreme neutron radiation damage

Amorphous fused silica (a-SiO 2 ) optical fibers, with and without inscribed Bragg gratings, were interrogated using infrared (~1550 nm) optical backscatter reflectometry during ~25 days of intense neutron irradiation to a fast (energy > 0.1 MeV) neutron fluence of ~10 21 n/cm 2 , or ~1.5 atomic displacements per atom. The reflected light amplitudes in Ge-doped core telecommunications fiber dropped below detection limits (>15 dB attenuation) within 3 days of irradiation (~10 20 fast n/cm 2 ). Here, amplitudes from a pure silica core, F-doped silica cladding fiber reached equilibrium levels ~1.5–2 dB higher than pre-irradiation values, whereas Bragg gratings inscribed in the same fiber using a femtosecond laser (point-by-point method) suffered > 45 dB attenuation. Blue wavelength shifts were initially consistent with previous radiation-induced compaction models but increased linearly with increasing neutron fluence (no evidence of saturation) beyond 10 20 n/cm 2 and exceeded 0.6%, which corresponds to >1,000 °C drift if used to measure temperature changes.

36 MATERIALS SCIENCE↗