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  • 1
    Electronic Resource
    Electronic Resource
    Radiation hardening of pure-silica-core optical fibers by ultra-high-dose γ-ray pre-irradiation (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 5008-5013 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Induced optical absorption in three SiO2-core/SiO2:F-clad fibers (two high-OH, one low-OH) and one SiO2:Ge-core fiber was investigated in situ in the range 415–1100 nm during repeated 60Co γ-ray exposures to doses (approximately-greater-than)1 MGy(Si). Injected visible light (∼5 μW) was maintained during the first and second irradiations at ∼27 °C and an intervening period out of the source; an additional irradiation and subsequent out-of-source period were monitored with the light off. Bleaching effects due to radiation alone, light alone, and the synergism of light plus irradiation were independently observed. All visible-range damage in the pure-silica-core fibers in excess of a few tens of dB/km was deduced to arise from activation of precursor states including chloride impurities and process-induced defects. These extrinsic color centers were eventually eradicated and the fibers permanently rad hardened after a cumulative radiation dose of 8.3×106 Gy and a visible light fluence of ∼1.4 mW h. The hardening mechanism is here ascribed to radio- or photostimulated complexing of the extrinsic centers with radiolytically derived interstitial oxygens.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359310
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  • 2
    Electronic Resource
    Electronic Resource
    Radiation-induced defect centers in high-purity GeO2 glass (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 2264-2268 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Defect centers induced in GeO2 glass by either 100-KeV x rays at 77 K or γ rays at room temperature were studied by electron-spin resonance. The model of a singly charged oxygen vacancy defect center for the Ge E' center (g(parallel) =2.0012, g⊥ =1.9945) was confirmed by the observation and computer simulation of the 73Ge hyperfine structure associated with this center. The evolutions of the Ge E', peroxy radical, and nonbridging oxygen hole centers were studied by isochronal thermal annealing. Surprisingly, the Ge(2) center, a defect previously known only in Ge-doped silica, and an additional center with a hyperfine coupling constant half that of the Ge E' center were found in pure GeO2 samples irradiated at 77 K; these, too, were studied by isochronal thermal annealing and computer simulation. Structural models for these centers are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.339481
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  • 3
    Electronic Resource
    Electronic Resource
    Radiation-induced defect centers in glass ceramics (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 507-514 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron spin resonance (ESR) was used to characterize the radiation-induced defect centers in low-thermal-expansion glass ceramics, including two types of Zerodur and Astrositall. The observed ESR spectra can be associated with different types of defect centers: a Zn+ center, several types of oxygen hole centers (OHCs), an aluminum-oxygen hole center (Al-OHC), an Fe3+ center, Ti3+ and Zr3+ centers, and three types of As centers. An Sb4+ center, which is not observed in Zerodur, is tentatively identified in Astrositall. From the effect of crystallization on the observed defect concentrations in Zerodur and computer simulation of the spectral lines of some of the centers, we infer that among the nine defect centers observed in the Zerodurs, the As-associated centers are located in the glassy phase and/or at the interface between the glassy and crystalline phases, Zn+ and Al-OHC are in the crystalline phase, and the rest (including most of the OHCs) are in the glassy phase. Radiation-induced compaction in these materials appears to be related to the generation of OHCs in the glass phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343132
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  • 4
    Electronic Resource
    Electronic Resource
    Radiation effects on a low-thermal-expansion glass ceramic (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 3488-3490 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron-spin-resonance and density gradient column techniques have been used to measure and characterize the effect of radiation on the electronic and mechanical properties of a low-thermal-expansion glass ceramic. Defect centers attributed to Zn+, oxygen hole centers (OHCs), Fe3+, Ti3+, and/or Zr3+, and two types of centers associated with arsenic have been observed; the radiation-induced compaction has been tentatively correlated with the OHC concentration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.339272
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  • 5
    Electronic Resource
    Electronic Resource
    Electron trapping in amorphous SiO2 studied by charge buildup under electron bombardment (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 57 (1985), S. 5139-5144 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron bombardment of thick pure SiO2 induces the buildup of a negative charge which can be observed through a "mirror'' effect in a conventional Auger scanning microscope. A mechanism for the creation of this charge is proposed in terms of trapping of an electron in defects due to the irradiating beam. The influence of temperature is studied on amorphous and monocrystalline SiO2. The temperature dependence of the existence of high negative charge shows around 270 °C an anomalous effect which depends on the irradiation time. The role of electronic excitation to produce defects in silica is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.335247
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  • 6
    Electronic Resource
    Electronic Resource
    Formation of interface traps in metal-oxide-semiconductor devices during isochronal annealing after irradiation at 78 K (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 7434-7442 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the mechanisms of interface trap (Nit) formation in metal-oxide-semiconductor devices during isochronal annealing after irradiation at 78 K. Two distinct Nit formation processes are observed at 120 and 250 K. After irradiation but before annealing, some samples were injected with electrons to remove all the radiation-induced positive oxide charges. In these samples, the Nit formation process at 250 K is nearly eliminated, in agreement with previous reports, but the lower-temperature 120 K process increases substantially. Results are explained using a hydrogen model. We also discuss the use of substrate hot-electron injection, which is used to annihilate the radiation-induced positive charge, in some detail.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349739
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  • 7
    Electronic Resource
    Electronic Resource
    Post-irradiation cracking of H2 and formation of interface states in irradiated metal-oxide-semiconductor field-effect transistors (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 658-667 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Molecular hydrogen is alternately introduced into and removed from the gate oxide of irradiated metal-oxide-semiconductor field-effect transistors at room temperature by changing the ambient between forming gas (10/90% H2/N2) and nitrogen. Using charge pumping, it is observed that H2 causes a simultaneous buildup of interface states and decrease of trapped positive charge. The results are explained by a reaction sequence in which H2 is cracked to form mobile H+, which under positive bias drifts to the Si/SiO2 interface, and reacts to produce a dangling-bond defect. The rate limiting step over most of the time domain studied is the cracking process. Two types of cracking sites are modeled by molecular orbital calculations: oxygen vacancies (E' centers) and broken bond hole traps (BBHTs). Initial- and final-state energies, as well as the activation energies, are calculated. The calculations indicate that the latter is the more likely H2 cracking site. The combined experimental and theoretical results suggest that at least 15% of the trapped positive charge is at sites similar to the BBHT sites. Implications of the model and similarities between interface-state formation by cracked H2 and irradiation are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353348
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  • 8
    Electronic Resource
    Electronic Resource
    An electron-spin-resonance study of γ-irradiated barium galliosilicate glasses (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 4852-4859 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Electron-spin-resonance spectroscopy has been used to study the structure of radiation-induced defects in a barium galliosilicate glass compositional series of BaO/Ga2O3=1.0 and 20–80 mol % SiO2. Spin-Hamiltonian parameters derived from computer line-shape simulations have been used to identify three oxygen-associated hole centers: a gallium-oxygen hole center and two variations of silicon-oxygen hole centers. Each of these defects contains an unpaired electron in a nonbonding oxygen p orbital. The compositional dependence of the ESR data is consistent with a gradual change from a Ga-based tetrahedral network to a Si-based tetrahedral network as the silica content is increased.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462775
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  • 9
    Electronic Resource
    Electronic Resource
    γ-radiation resistance of aluminum-coated all-silica optical fibers fabricated using different types of silica in the core (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 322-324 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Induced loss spectra in four Al-coated large-core optical fibers are measured in the range 380–1000 nm during and after 60Co γ irradiation. These fibers had F-doped-silica claddings and synthetic silica core materials produced by different technologies. Measurements were carried out independently in Washington and Moscow using differing techniques but yielding very similar results. The highest radiation resistance is exhibited by two fibers with extremely low OH and Cl contents in their cores, one with a core material containing 0.5 mass % of fluorine, fabricated specially for this study, and one based on KS-4V silica, an original technology developed in Russia. The latter fiber demonstrates a rather flat induced loss spectrum in the visible region at a level of 2–2.5 dB/m for γ-ray doses of ∼10 MGy(Si). © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.118047
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  • 10
    Electronic Resource
    Electronic Resource
    On the spectral reflectance and maturation darkening of lunar soils (1976)
    Springer
    Earth, moon and planets 15 (1976), S. 15-30 
    Details
    ISSN: 1573-0794
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Optical absorption and diffuse reflectance spectra were obtained for simulated lunar glasses of four different compositions, both in their as-quenched (reduced) states and following mild subsolidus oxidation. The transmission spectra, when normalized by the FeO content of the glasses, differed from one another only in the relative intensity of an unresolved band in the UV. For fixed melting conditions the strength of this band in the as-quenched glasses increased with increasing FeO, or with increasing TiO2 for a fixed FeO content. Electron spin resonance (ESR) experiments have demonstrated the absence of Fe3+ or Ti3+ and the presence of metallic iron in these materials; all other transition-group elements were excluded in preparation. The unresolved UV absorption edge in the as-quenched reduced glasses is therefore tentatively ascribed to Fe2+→Ti4+ intervalency charge transfer transitions. A similar UV edge was also produced by oxidation, leading to the conclusion that the assignment of this band would be ambiguous in the absence of an independent determination of the valence states of Fe and Ti. The relationship between the transmission spectra of polished samples and the reflectance spectra of sieved powders of the same materials is shown to be well described by the Kubelka-Munk approximation. Using this insight, it is possible to understand the spectral characteristics both of oxidation darkening of synthetic glass powders and of maturation darkening of lunar soils in terms of (1) the growth of the aforementioned charge transfer band(s) and (2) the development of opaque surface phases. It is shown that mechanism (1) is of primary importance in lunar highland materials and that mechanism (2) dominates in mare materials. The present results, coupled with previous findings, suggest that lunar soil maturation darkening may result from vitrification only if accompanied by (a) enrichment in the elements Fe and Ti, (b) changes in valence states of these elements, (c) partial crystallization of opaque phases such as iron, ilmenite or magnetite, or (d) a combination of (a), (b), and (c).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00562469
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