Γ-irradiated Glasses Research Articles

Threshold restoration effects in γ-irradiated chalcogenide glasses

The influence of annealing temperature Ta on the optical absorption edge in the previously γ-irradiated glasses of Ge–Sb(As)–S ternaries of pseudobinary ‘stoichiometric’ Sb(As)2S3–GeS2 and non-stoichiometric Sb(As)2S3–Ge2S3 cut-sections is studied. It is established that the post-irradiation thermally produced changes of the optical absorption edge differ in various Ta regions. Threshold restoration effects are found beginning from some intermediate onset temperature Ton for all investigated glasses. Compositional features of the apparent activation energies determined in corresponding Ta regions are analyzed. A possible mechanism for the observed effects is discussed.

Kinetics of Accumulation and Decay of Paramagnetic Centers in γ-Irradiated Doped Phosphate Glasses

The dose dependences and decay kinetics of PO42− and PO32− paramagnetic centers and radiation-reduced europium Eu(3+)− in γ-irradiated phosphate glasses of composition 4Na2O · La2O3 · 7P2O5 doped with europium are studied. The data obtained are discussed within the trapping volume model in the approximation of short irradiation duration. It is shown that the trapping volume parameter v decreases with increasing irradiation dose. A physical interpretation of the parameter v is proposed.

Alkali ion exchange in γ-irradiated glasses

The alkali ion exchange of γ-irradiated glasses was investigated using the structural energy barrier model for ion exchange of glasses. It is shown that rates of alkali ion exchange have a non-Arrhenius behaviour depending both on irradiation dose and dose rate. For this reason some effects cannot be simulated by external irradiation and require in situ measurements. Higher doses and dose rates of γ-radiation lead to increased ion exchange rates. Significant changes occur in the activation energies demonstrating a many times decrease depending on glass composition. Radiation-induced changes are higher at relatively low temperatures being diminished by increased glass temperature. Numerical estimations show that changes in alkali ion exchange kinetics occur below the glass network damaging doses.

Specific features of the induced absorption spectra of fluoroaluminate glasses doped with samarium ions

The induced optical absorption spectra of γ-irradiated fluoroaluminate glasses doped with Eu3+ and Sm3+ ions are investigated. It is shown that Sm3+ ions in fluoroaluminate glasses are protector ions contributing to the suppression of induced absorption in the optical absorption spectra of the studied glasses. It is revealed that the induced optical absorption spectra of the glass samples heat treated at T = 583°C contain two absorption bands with maxima at 300 and 480 nm, which correspond to radiation-reduced (Sm3+)–. The concentration of color centers produced by γ-radiation in fluoroaluminate glasses is estimated. It is demonstrated that prolonged heat treatment of the glass at T = 638 K brings about the decay of (Sm3+)– centers followed by the destruction of the samples.

Radiation-Induced Paramagnetic Centers in the Glasses Of CaO-Ga2O3-GeO2 System

The X-band (v ≅ 9.4 GHz) ESR spectra of the UV-, X-, and γ-irradiated glasses of CaO-Ga2O3-GeO2 system with compositions similar to Ca3Ga2Ge3O12, Ca3Ga2Ge4O14, and Ca3Ga2O6 crystals have been investigated at 300 and 77 K. It was shown that X- and γ-irradiation of the Ge-contained glasses induce simultaneously electron and hole paramagnetic centers, stable at room temperature. The UV-irradiation of Ge-contained glasses leads to the generation of stable centers of electron type, whereas the X- and γ-irradiation of glasses with Ca3Ga2O6 composition induces stable hole centers, exclusively. The electron centers are assigned to E′ (Ge) centers with different local environments. ESR spectrum of hole centers is ascribed to O− centers, localized on non-bridging oxygen of the glass network. The E′ (Ge) and O− centers show high thermal stability in the CaO-Ga2O3-GeO2 glass network. The obtained ESR spectra are described by spin Hamiltonian with g-factor of axial and rhombic symmetry for the E′ (Ge) and O− centers, respectively. The nature, electron structure and some formation peculiarities of the radiation defects in CaO-Ga2O3-GeO2 glasses are discussed in comparison with other glasses as well as Ca3Ga2Ge3O12 and Ca3Ga2Ge4O14 crystals.

Correlation between the green photoluminescence band and the peroxy radical in γ-irradiated silica glass

We studied the origin of a green photoluminescence (PL) in silica glass at about 2.25 eV using electron spin resonance. The 2.25 eV PL band (lifetime: ∼300 ns, full width at half maximum: ∼0.2 eV) appears strong in γ-irradiated high-oxygen content silica glass suggesting that this PL is associated with a large surplus of oxygen states in silica glass. We investigated the correlation between the 2.25 eV PL band and the peroxy radical by the isochronal annealing method. Peroxy radicals are formed by the O3≡Si–O–O• bond (•: unpaired electron) and the small “peroxy radical” (SPR) bond in silica glass. Based on the annealing characteristics of the 2.25 eV PL band and the peroxy radical, we suggest that the PL band is associated with a surplus of oxygen defects formed by the SPR rather than the O3≡Si–O–O• bond.

Correlation between the Red Photoluminescence Band and the Oxygen-Deficient-Associated Defect Centers in γ-Irradiated Silica Glass

The origin of the red photoluminescence (PL) band at approximately 1.8 eV in the PL spectra of oxygen-deficient-type silica glass was studied using electron spin resonance (ESR). The ESR spectrum of oxygen-deficient-type silica revealed hyperfine (hf) interactions between the unpaired electrons of radicals and neighboring 29Si atoms. Eight hf lines were recorded at approximately 40.9, 9.5, 7.6, 4.26, 3.0, 2.5, 1.6, and 1.06 mT. The 40.9 mT line arises from the primary 29Si hf structure of the E′ center (O3≡Si↑, ↑: unpaired electron). The other lines are associated with oxygen-deficient-associated defect centers [Si clusters or SiOx (x<2) structure]. We studied the relationship between the intensity of the 1.8 eV PL band and the intensity of the ESR signal which arises from the oxygen-deficient-associated defect centers, in various silica glass synthesized by various methods in the presence of different amounts of oxygen. We also studied the spatial distributions of the 1.8 eV PL band intensity and the ESR signal intensity in one silica glass sample. These results suggest that the 1.8 eV PL band in the PL spectrum of oxygen-deficient-type silica glass is associated with the oxygen-deficient-associated defect centers in silica glass.

Photoconductivity induced by excitation of geminate trapped electrons in hydrocarbons glasses

Experimental data on photoconductivity in γ-irradiated 3-methylpentane glass are considered for the case when most radiation produced trapped electron forms geminate pairs with their parent positive ions. It is assumed that mobile electrons generated by photoexcitation of trapped electrons have an excess energy and there is a thermalized mobile precursor of stable trapped electrons which is governed by Smoluchowski's equation. The model allows to describe experimental data on photocurrent kinetics. It predicts that for germinate trapped electrons, apart from “free” or not germinate electrons, photocurrent dependes on the thermalization ranges of photoliberated electrons even if nonthermalized electrons are not affected by electric field.

Formation of Paramagnetic Defects in Oxide Glasses During the Bombardment of Their Surface with Charged Particles

ABSTRACTHeavy-ion bombardment of a glass surface is a conventional laboratory technique for producing damage of interest for radioactive waste encapsulation. At energy of order 100 keV such a bombardment simulates the damage produced by α-recoil nuclei and fission fragments resulting from the nuclear decay. The damage region is 100–500 nm depending on conditions of the bombardment.In the present work some results of EPR study of point defects formed in silicate, borate, borosilicate, phosphate and other oxide glasses irradiated with different charge particles (C, N, O, Ar. Mn, Cu, Pb) at energy E=150 keV and large total fluence of ions (up to 1017 cm-2) are reported. Electron paramagnetic resonance (EPR) is a very sensitive technique which gives an information on the structure of point defects and their content. It is shown that in some cases (for example, in borate glasses) the oxygen hole centers similar to ones observed in γ-irradiated glasses are formed after ion bombardment. However, in the majority of cases new defects which are not typical of γ-irradiated oxide glasses were found They were large molecular oxygen ions (O2-O3-O4-) located in the cavities formed under ion bombardment in the near surface layer of glass. It should be noted that the relative content of these defects is of the order of several tens per 1000 incident ions. This content decreases with increasing fluence and atomic mass of incident ions. It indicates indirectly that point defects are clustered when the damage of the near surface layer becomes strong. The formation of gaseous oxygen is possible in cavities of the damage surface layer.It was found that some elements (for example C, N and transition metals) form chemical compounds with oxygen. The migration of alkali ions promotes the formation of such compounds since the chemical compounds were detected by means EPR in glasses rich in alkali oxides.

29Si superhyperfine interactions of the E′ center: a potential probe of range-II order in silica glass

Abstract An electron spin resonance study has been carried out on E′ γ centers in γ-irradiated silica glasses of various 29 Si enrichments, with the object of measuring superhyperfine splittings due to 29 Si nuclei at the three closest silicon neighbors to the silicon of the unpaired spin. Experimental spectra obtained at X band (9.1 GHz) in the absorption mode and at Ka band (35.0 GHz) in the rapid-passage dispersion mode are compared with computer lineshape simulations based on a simple tight-binding model anchored to literature values of the so-called ‘weak’ 29 Si hyperfine splittings of the E′ 1 center in α-quartz. Surprisingly few E′ γ sites are found in the glasses to exhibit such ‘weak’ splittings. To reconcile this result with the model assumption made by Mozzi and Warren and the supporting analyses of Galeener, it is suppose that dihedral angles in glassy silica might be relatively uniformly distributed and uncorrelated with the SiOSi angle distribution in the undamaged glass but that backward puckering relaxations (similar to that calculated by Rudra et al. for the E′ 2 center in quartz) may be pervasive at E′ γ (oxygen vacancy) sites in glassy silica, causing dihedral angles in the range 100 ≲ α 1 ≲ 140° to be ‘read out’ in the present experiment as falling in the range 80 ≳ α 1 ≳ 40°

Effect of γ-Irradiation on Optical Second Harmonic Intensity of Electrically Poled Silica Glass

Optical second harmonic generation has been observed in γ-irradiated and subsequently electrically poled silica glasses. The second-order nonlinear susceptibility, as well as the second harmonic intensity, increases with an increase in the γ-ray dose. The larger second harmonic intensity of γ-irradiated silica glasses may be related to the defects created by γ-irradiation.

Electronic spectra of C 70 anions produced in γ-irradiated organic glasses at 77 K

The electronic spectra of C 70 anions were observed in γ-irradiated methylcyclohexane and MTHF glasses at 77 K. The band at 1386 nm in methylcyclohexane was assigned to C − 70. The spectrum in MTHF consisted of two bands at 1184 and 1377 nm. The former band was tentatively ascribed to C 2− 70. The values of ϵ G obtained are 265±40, 230±45 and 217±45 M −1 cm −1 at 1386, 1377 and 1184 nm, respectively.

Low energy electron localization in hydrocarbon glasses. Method of photoassisted ion pair separation

Experimental results on increase of the probability of geminate ion pair separation into free ions caused by photoexcitation of trapped electrons in γ-irradiated 3-methylpentane glasses at 77 K are discussed. The increase is associated with injection of “hot” electrons in the medium. After thermalization the motion of the electrons is suggested to be governed by Smoluchowski's equation until stable trapped electron states occur. The dependence of the mean-square thermalization length on the electron energy in the interval 0.1–1.5 eV and the mean-square length (45 Å) of thermalized precursor of stable trapped electrons are estimated. It is concluded that electron localization precedes to total thermalization and is effective at electron energies <0.1 eV.

Electronic and Molecular Structure of the C8H Valence Isomers 1,3,5‐Cyclooctatriene+· and Bicyclo[4.2.0]octa‐2,4‐diene+· from their Electronic absorption Spectra in Freon

AbstractThe molecular cations of 1,3,5‐cyclooctatriene (COT+·) and bicyclo[4.2.0]octa‐2,4‐diene (BCO+·) can be observed intact in γ‐irradiated Freon glasses, as opposed to Ar matrices where ionization is accompanied by extensive rearrangements. This proves the superiority of the Freon‐glass method for the generation of metastable primary cations. The electronic absorption (EA) spectra reveal a) that a previous analysis of the BCO+· electronic structure on the basis of the ultraviolet photoelectron (UP( spectrum of BCO was incomplete, and b) that COT undergoes planarization upon ionization, in accord with qualitative expectations and MNDO calculations. A previously proposed LCBO model was used to assess the influence of the above geometry change on the electronic structure of COT+·.

The isothermal luminescence of γ-irradiated 3-methylpentane glass at 77 K

The isothermal luminescence (ITL) at 77 K of pure 3-methylpentane was investigated. The influence of dose on ITL intensity, spectral distribution and decay was examined. The effect of pre-irradiation dose on ITL was found. The results were explained assuming the recombination of e - t -cation (in the low dose range) and anion-cation (in the high dose range, ⪞ 10 23 eV dm -3). The recombining anions and cations are formed as a result of charge transfer from primary ions to the radicals as well as to stable radiolysis products.

A photoconductivity study of trapped electrons in γ-irradiated hydrocarbon glasses at 77 K

Photoconductivity spectra of trapped electrons in γ-irradiated 3-methylpentane, 2-methylpentane, 3-methylheptane, and 3-methylpentane–methylcyclohexane (1:9 volume ratio) glasses at 77 K were measured. From the comparison of photoconductivity and optical absorption spectra in these systems we have obtained relative values of quantum efficiencies for a trapped electron in the ground state to be excited to the conduction band by photo-induced transition. For electrons stably trapped, we have measured the ranges of trap depths from the shallowest to the deepest in these systems.

Excimer emission in the isothermal luminescence of γ-irradiated hydrocarbon glasses at 77 K

A new method of excimer generation, using the radiation technique, is described. Excimer emission was observed in the isothermal luminescence of hydrocarbon matrices doped with naphthalene, γ-irradiated at 77 K and after annealing at higher temperature.

Relative Electron-capture Efficiency of Disubstituted Benzene in γ-Irradiated MTHF Glass at 77 K

Abstract The relative electron-capture efficiencies of disubstituted benzenes were measured by a competitive method. It was found that the efficiencies of the disubstituted benzenes are correlated with the reactivity towards nucleophilic species as expressed by Hammett’s substituent constant. The logarithmic values of the efficiency are roughly proportional to the polarographic half-wave reduction potentials and to the electron affinities.

EPR and optical spectra of gamma-irradiated sodium-silicate glasses containing copper oxide

The effects of an addition of CuO on the intrinsic and induced EPR and optical absorption spectra of γ-irradiated sodium-silicate glasses melted under different redox conditions are studied. It is shown that the CuO impurity blocks the formation of radiation-induced centers associated with the intrinsic defects of glass matrix. A new paramagnetic centre appears in the sodium-silicate glasses containing CuO after γ-irradiation. This center is the hole trapped at the Cu 1+ ion, and its spectral parameters are different from ones of the Cu 2+ ions obtained by chemical oxidation of copper.

Change in Intensity of Radiophotoluminescence in Dosimeter Glass by Intense Laser Light

Luminescence is investigated in dosimeter glasses under intense excitation by a N2 laser. The maximum excitation intensity is about 1 MW/cm2. Decrease and increase in emission intensity are observed in γ-irradiated and nonirradiated glasses, respectively. The decreasing curves are analyzed by using simple rate equations. The increase in emission intensity is attributable to the creation of luminescent centers by two-photon excitation caused by intense laser light. These effects are negligible under weak excitation (<100 kW/cm2).