摘要:

Channeling and back-scattering techniques were used to study single crystals of α-Al2O3and MgO following bombardment with Pt- (or Xe-)ions of 30 keV energy and doses between 9 × 1015and 8 × 1016ions/cm2, as used for catalytic investigations. The MgO crystals showed saturation damage after implantation with the lower dose. Damage recovery proceeded progressively with increasing temperature and was not complete before 1300°C was reached. The Pt formed coherent precipitates. In contrast, a quasi-amorphous zone was formed on ion bombarded Al2O3. Outdiffusion of the impurity and recovery of the bombardment damage started at ∼650°C, the temperature of the phase change to the recrystallized state. At temperatures in excess of 900°C, the Pt precipitated into small single crystal grains of near spherical shape. The results can be used to interpret the catalytic behavior of the systems Pt/single crystalline support.

ISSN:0033-7579    

DOI:10.1080/00337578208216811

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Solid benzene has been bombarded with several inert gas ions at various energies ranging between 15–100 keV. Under these conditions the energy deposition (η) which occurs via nuclear collisions ranged between 4 × 10−3÷ 1 of total energy loss. After implantation many products have been found in the target, and good correlation between the C13product yield and η has been found. This correlation is explained in terms of different fragmentation events which occur after electronic and nuclear energy deposition.

ISSN:0033-7579    

DOI:10.1080/00337578208216812

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Ion implantation can be used to introduce network damage and to alter the chemical composition in glasses. Structural changes can be inferred from IR measurements near 1000 cm−1and by optical absorption near 2150 Å. Implantation-induced damage decreases the implanted volume in fused silica with consequent changes in the refractive index, the near-surface hardness, and the tensile surface stress. Prior work in these areas is reviewed. Implantation into alkali silicate glasses depletes the alkali content in the implanted region. These changes allow preferential surface crystallization in Li2O-2SiO2glasses. Crystallization of amorphous SiO2 can be induced by implantation of Li. Insight into the crystallization process is obtained by following the associated ion movement by elastic recoil detection (ERD) and optical techniques. Implantation of 20keV H shows that saturation of implanted H-sites in fused silica occurs at about 2.2 × 1021H/cm3in agreement with free volume estimates of the maximum number of available interstitial sites. Details of H and D interactions in fused silica were studied as a function of fluence and temperature. Results are of interest in studies of corrosion in glasses considered for nuclear waste encapsulation and for components in fusion reactors.

ISSN:0033-7579    

DOI:10.1080/00337578208216813

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Soda-lime glasses have been implanted with 50 keV Az ions. Modifications induced on the glass surface have been studied as a function of implanted dose, with particular regard to optical, chemical and mechanical properties.

ISSN:0033-7579    

DOI:10.1080/00337578208216814

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The present paper summarizes recent experiments at the JRC, aiming to determine the relative damage effects produced in a-SiO2 by particles of different mass and energy, so as to correlate typical defects with specific production mechanisms. By systematic analysis of optical absorption spectra, the main colour centres that are currently associated with primary irradiation effects were characterized. Centres responsible for the B2-band (5.04 eV) and E'-band (5.78 eV) were quantitatively investigated with respect to particle type, production yield and saturation behaviour. Arguments taken from energy loss and dpa seem to suggest that the E' centre is based on a stable structural substrate, which is not reconciled with simple ideas of a broken bond. The B2centre is confirmed to be associated with atomic defects produced by collisions. New determinations in the vacuum u.v., performed on heavy-ion irradiated samples, seem to put this centre in quantitative relationship to a centre responsible for a 7.15 eV absorption.

ISSN:0033-7579    

DOI:10.1080/00337578208216815

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

This paper describes a series of annealing experiments devoted to the study of the thermal behaviour of B2and E' centres produced by heavy-ion irradiations in v-SiO2. Thermal bleaching of the B2component is shown to be complete and irreversible at relatively low temperatures (⩽500°C). On the other hand, bleaching of E' in the same range is reversible and the corresponding absorption band can be entirely recovered in subsequent electron irradiations, suggesting the existence of a stable precursor defect for this centre. By alternating isochronal annealing cycles with electron re-irradiations, the annealing of such defects was investigated up to 1000°C, taking care to compare the behaviour of the heavy-ion damaged material with that of undamaged material. The results seem to suggest a structural difference between pre-existing E' precursors of normal SiO2and those produced in excess by displacing radiation, the latter being characterized by a distinct process of destruction with an activation energy Q ≳0.6 eV.

ISSN:0033-7579    

DOI:10.1080/00337578208216816

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

High voltage electron microscopy studies have been performed on irradiated pure silica and borosilicate glasses to check their long-term stability when these materials are employed near high energy radioactive sources, such as in fusion reactors and during the storage of nuclear waste. The intense energetic beam of electrons produced by the Harwell 1 MeV microscope, ranging from 1017to 1020e/cm2/s has been focused upon specimens of various composition and impurity content at different temperatures up to about 850°C. Pure silica samples have also been bombarded with 46.5 MeV Ni+6 ions at the Variable Energy Cyclotron. It is found that while no significant changes are detectable in pure irradiated silica, clear evidence is present in complex borosilicate glasses for the growing of large defect clusters (over 1000 Å, resembling gas bubbles) after electron doses of about 8.5 × 1019e/cm2and dose rates exceeding 2 × 1018e/cm2/sec. Moreover, small regions, about 100 Å wide, scattering electrons more than the matrix are also present. The nature of this fine microstructure has been established as a phase separation into crystalline tridymite. The observations are discussed in terms of their dependence on temperature, sample thickness, dose and dose rates.

ISSN:0033-7579    

DOI:10.1080/00337578208216817

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

This paper seeks to update previous reviews of the effects of ionizing radiation on amorphous insulators. The electronic and atomic structures of radiation-induced defect centers (trapped electrons or holes) are discussed primarily in terms of data deriving from the technique of electron spin resonance. Emphasis is placed on important fiber-optic materials (pure and doped fused silicas) and attention is directed to the problem of relating radiation-induced optical absorption bands to specific defect structures.

ISSN:0033-7579    

DOI:10.1080/00337578208216818

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The various methods of optical absorption spectroscopy, Rutherford back-scattering, transmission electron microscopy and X-ray diffraction, have been associated to study the high-dose ion implantation (150 keV, 1017ions cm−2) phenomena in SiO4Mg2single crystals. After thermal annealing at high temperature under vacuum or in atmosphere, different new phases appear:

ISSN:0033-7579    

DOI:10.1080/00337578208216819

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Radiation induced effects in glass-rods and fiberoptics have been studied to determine parameters affecting the application of these materials in nuclear technology, i.e. as fiberscopes for visual inspection in severe radiation environments. Different glass and fibertypes have been exposed to fission product gamma radiation. The radiation induced transmission loss was measured with a spectrophotometer and then different annealing methods were examined to improve the transmission properties again. Especially the changes in glass and fiber recovery vs. time as a function of radiation dose and annealing temperature were investigated. Annealing experiments were performed exposing the samples either to temperature treatment or to various light sources such as quartz lamp, arc lamp or UV-laser for optical annealing. The transmission recovery was then investigated either as a function of annealing temperature or of exposure time to the light sources. The results allow conclusions on the design and composition of optical fiber endoscopes to be used in severe radiation environment where image transmission is required in the presence of high level nuclear radiation.

ISSN:0033-7579    

DOI:10.1080/00337578208216820

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor