Electron-irradiated Quartz Research Articles

Radiation-damage-induced defects in quartz. I. Single-crystal W-band EPR study of hole centers in an electron-irradiated quartz

Single-crystal W-band electron paramagnetic resonance (EPR) spectra of an electron-irradiated quartz, measured at room temperature, 110 and 77 K, disclose three previously reported hole centers (#1, G and an ozonide radical). The W-band EPR spectra of these three centers clearly resolve six magnetically nonequivalent sites each, whereas previous X- and Q-band EPR studies reported Centers #1 and the ozonide radical to consist of only three symmetry-related components and interpreted them to reside on twofold symmetry axes in the quartz structure. The calculated g matrices of Center #1 and the ozonide radical show that deviations from twofold symmetry axes are <10°, which are probably attributable to distortion related to neighboring charge compensating ions. The W-band EPR spectra of Center G not only result in improved g matrices but also allow quantitative determination of the nuclear hyperfine (A) and quadrupole (P) matrices of its 27Al hyperfine structure that was incompletely resolved before. In particular, the g-maximum and g-minimum principal axes of Center G are approximately along two pairs of O–O edges of the SiO4 tetrahedron, while the unique A principal axis is approximately along a Si–Si direction. These new spin-Hamiltonian parameters suggest that Center G most likely involves trapping of a hole between two oxygen atoms related to a silicon vacancy and stabilized by an Al3+ ion in the neighboring tetrahedron (hence an O2n−–Al3+ defect, where n is either 1 or 3).

Spin–spin relaxation times of the [formula omitted] center in quartz with and without irradiation: implications for the formation process of the oxygen vacancies in nature

The pulsed ESR technique was employed in the present study to obtain the spin-spin relaxation times of the E 1 ′ center (an unpaired electron at an oxygen vacancy) in natural quartz with and without irradiation. The relaxation times of the heat treated E 1 ′ center in natural unirradiated quartz of a granite and of uranium ore were 3.5– 7.1 μ s . Electron and gamma ray irradiated quartz showed the relaxation times of 7.1– 15.7 μ s while He ion implanted quartz showed 1.0– 2.0 μ s , much less than the other samples. The intensity of the E 1 ′ center increased in stepwise heating up to 300 ∘ C before decreasing above that temperature except for He implanted sample which showed monotonic decrease on heating. The present experimental results showed that the characteristics of the E 1 ′ center created by high linear energy transfer (LET) radiation is different from that by low LET radiation, suggesting that, in nature, the oxygen vacancies are created by low LET radiation, i.e. external beta and gamma rays, rather than by alpha particles and alpha recoil nuclei.

Insulator size effect on electron-irradiated quartz

A time-resolved current experiment measuring separately the surface and bulk currents flowing through an insulating sample under electron beam irradiation employing a scanning electron microscope is performed to investigate charging and flashover phenomena. A set of metallic apertures of various values of radius are used to vary the area of the insulator. It is observed that the bulk current decreases monotonically with time until reaching a constant value, while the surface current exhibits two different trends: decreasing monotonically with time, and decreasing with time at first and then increasing. Such observations are related to the establishment of a dynamic equilibrium between electron trapping and detrapping, as well as the flashover behavior, and depends on the insulator size and the experimental conditions.

Quantitative Hrem of Electron-Irradiated Quartz

AbstractThe progress of heterogeneous amorphization of electron-irradiated quartz was studied in situ by high-resolution electron microscopy (HREM). The transformation front appears surprisingly sharp when viewed close to edge-on, but the apparent morphological evolution when aperiodic and periodic material overlap in projection is one in which gradual changes in image regularity are observed. Electron-microscopical contrast obtained in HREM irradiations was interpreted quantitatively, through the use of image contrast simulations. When the amorphized portion occupies less than about two-thirds of the total thickness, the HREM images continue to appear crystalline. Only when the amorphized thickness fraction exceeds about two-thirds does the resultant image contrast show mainly non-crystalline features.

HREM of Electron Irradiated Quartz

ABSTRACTIn situ electron irradiation has been carried out in transmission electron microscopes to monitor the dynamic evolution of α-quartz during the transition to the metamict state from the crystalline state. Crystals of different orientations were examined. HREM images were digitized and Fourier transformed to monitor degradation of periodicities. The final uniform metamict structure was characterized by radial distribution functions obtained from energy-filtered electron diffraction.

Ultrasonic measurements of the variation of the velocity of sound in electron-irradiated quartz: A quantitative analysis to the tunneling model

A quantitative analysis of measurements of the variation of the velocity of sound in electron-irradiated quartz shows that the data can be well described with the tunneling model. The TS-parameters are obtained from the numerical fittings and their values found from data for two different frequencies are consistent with each other. The density of states is much smaller than in vitreous silica and also smaller than in neutron-irradiated quartz for a similar dose. The coupling parameter γ ℓ is of the same order of magnitude as in vitreous silica, but slightly smaller.

Precision ultrasonic velocity measurements for the study of the low temperature acoustic properties in defective materials

A very precise method for measurements of the variation in the velocity of sound in solids in the 500 MHz frequency range is presented. The method is based on a pulse interference method and allows the observation of relative velocity changes of the order of 10 −7 or better. The availability of this method made it possible to detect the “glassy” behaviour of the low temperature velocity of sound in electron-irradiated quartz and in neutron-irradiated quartz for low doses and to fit the results to the tunnelling model. The fittings give more convincing evidence that the tunnelling states in electron-irradiated quartz are of similar nature to those in neutron-irradiated quartz. The density of states, however, is very much smaller in electron-irradiated quartz than in neutron-irradiated quartz for a similar dose.

Ultrasonic-phase-velocity measurements in electron-irradiated quartz.

Precision measurements of the ultrasonic velocity change as a function of temperature were carried out in electron-irradiated quartz (dose=1.0\ifmmode\times\else\texttimes\fi{}${10}^{20}$ e/${\mathrm{cm}}^{2}$, E=3 MeV) for two frequencies: 648 and 480 MHz. Between 0.33 and 2 K, a frequency-independent logarithmic increase of the velocity is observed. The effect is very small, but clearly indicates the presence of the resonant interaction of tunneling states with phonons. The experiment shows that tunneling states of a two-state nature are present. In addition, the effect of the relaxation process on the velocity is observed and shows that the tunneling states are of the same nature as in glasses. A comparison with neutron-irradiated quartz indicates that similar tunneling states are induced by electrons and neutrons, in spite of the different disordering processes. It is suggested that the electron-induced Frenkel pairs provide the necessary freedom for rearrangements and rotations of the tetrahedra, which can be at the origin of the tunneling states.

Backward-wave phonon echoes in irradiated quartz

The authors have observed parametric omega - omega phonon echoes in neutron- and electron-irradiated quartz at 9 GHz and at 1.5 K. Power dependences of the echo amplitude can be explained by saturation of two-level systems and the similarity between the results for the two materials suggests that point defects rather than amorphous-like regions, which are not created in electron-irradiated quartz, are the responsible centres.

Low-Temperature Anomalies in Glasses and the Related Study of Electron and Neutron Irradiated Quartz

Low-Temperature Anomalies in Glasses and the Related Study of Electron and Neutron Irradiated Quartz

Two-level systems in electron-irradiated quartz.

The longitudinal ultrasonic attenuation in electron-irradiated crystalline quartz (dose of 1.0 x 10/sup 20/ e/cm/sup 20/, E-italic = 2 MeV) was measured in the temperature range 1.4--300 K, at a frequency of 640 MHz. The data show conclusive evidence for the existence of two-level systems, similar to those in glasses. A relaxation attenuation is observed, giving rise to a T-italic/sup 3/ behavior at the lowest temperatures that levels off to a shoulder at about 10 K. The derived density of states is smaller than that in vitreous silica.

Positron annihilation lifetimes in irradiated crystalline quartz versus the 'glassy' thermal conductivity

Positron annihilation lifetimes have been measured in crystalline quartz samples after electron, fast neutron and gamma irradiation. The samples were those used for former thermal conductivity measurements or those which had been irradiated together with the samples on which dynamical studies have been carried out, so that their 'glassy' behaviour is known. It is found that gamma- and electron-irradiated quartz behaves as unirradiated quartz, while neutron-irradiated samples, even for a dose as low as 1*1018 neutrons/cm2, behave as a phase between quartz and vitreous silica. They show a long lifetime component as in vitreous silica. The positron annihilation behaviour, which is different for different kinds of irradiation, is not correlated to the low-temperature thermal conductivity behaviour, since the reduction in thermal conductivity in neutron- and electron-irradiated quartz is quite similar below 1K. This shows that the low-temperature thermal conductivity behaviour in irradiated quartz is not directly related to the presence of amorphous regions.

Evidence for the presence of two level systems related to point defects in electron irradiated crystalline quartz

Electron irradiation of crystalline quartz causes an additional thermal resistivity at low temperatures, which cannot be explained by the usual phonon scattering processes and is attributed to two level systems similar to those in glasses, but related to point defects.

Optical and Anelastic Absorptions and Resonator Frequency of Electron-Irradiated Quartz

For quartz resonators, optical (infrared, visible and ultra-violet) absorptions, anelastic absorptions and resonant frequencies were measured as functions of electron fluence. The data obtained nearly support King's equation of the frequency change and anelastic absorption, and also support a proposal by King et al. that the color center raises anelastic absorption at 100 K. It is very likely that, in the case of natural quartz, increase of anelastic absorption at 100 K, increase of the coloration intensity and decrease of infrared absorptions originating from Li+ and H+ ions are introduced by the detachment of Li+ and H+ ions from [AlO4]- centers, while in the coloration the synthetic quartz results from the detachment of alkali ions from [AlO4]- centers. The infrared absorption data show that complicated trapping and detrapping of H+ and alkali ions are occurring among various defects in both kinds of quartz during irradiation.