Steatite ceramic materials are promising for applications as dielectrics in setups exposed to ionizing radiation. These materials are multiphase systems which include crystalline and amorphous phases [1].Our aim in the present work was to study, by optical spectroscopy, the nature of radiation defects that form in steatite ceramic under high-dose y and mixed n-y irradiation. Steatite ceramic is opaque. For this reason, optical absorption, which in general is characterized by diffuse reflection, was studied by measuring the diffuse reflection spectra.Experimental procedure. SK-1 steatite ceramic has a fine-crystalline uniform structure. The main phases are crystals of magnesium metasilicate MgSiO 3 and glass with a complicated composition. Magnesium metasilicate crystals have an average grain size of 3-8 t.tm and occupy 60-70% of the volume of the ceramic [1, 2]. Samples in the form of 10xl0xl mm plates or 15 mm in diameter and 2 mm thick disks were used. The diffuse refleciion spectra of the unirradiated and irradiated ceramic samples were investigated in the wavelength range 200--700 nm using an SF-4 spectrograph with a PDO-1 diffuse reflection attachment, q[he light beam was detected with an FI~U-39 photomultiplier. Initial samples of SK-1 ceramic were used as the standard. The ceramic samples were irradiated by y-rays from 6~ and mixed.n-y irradiation from a reactor. The ),-dose was varied in the range 106-101~ R, the neutron fluence during reactor irradiation was 1017-102~ cm -2. The degree of light reflection was estimated from the relative reflection coefficient R = (lirrl Iunirr)• where lir r and Iuni~ ~ are, respectively, the intensity ofthe reflected light from the irradiated and unirradiated sample, respectively.Results and discussion. In the initial state the SK-1 steatite ceramic had a light color. After irradiation the samples acquired a brown color, whose density increased with the irradiation dose. After ),-irradiation additional absorption bands are observed in the UV region with a maximum at ~, = 220 and 260 nm and in the visible region of the spectrum with a maximum at 400-500 nm (Fig. 1). The intensity of the absorption bands increased with the y-dose (see curves 1-3 --107, 109, 1.5.10 l~ R, respectively). Similar absorption bands are also observed after irradiation in a reactor (1019 cm -2, curve 4). In previous investigations glass with a composition close to the glass phase of SK-1 ceramic was investigated by thermoluminescence and ESR. Thermoluminescence and ESR peaks were not observed in this glass after irradiation, but a paramagnetic absorption signal with g = 2.0012 was detected in the ceramic [3]. The presence of structural groups of the ceramic-oxygen framework in the magnesium metasilicate suggests that the observed absorption bands are associated with disruptions in the SiO 4 clusters [4]. Color centers, which absorb light near 220 and 260 nm, were observed in crystalline quartz and in quartz and silicate glasses under irradiation with ionizing radiation [5, 6]. They are associated ...

Because of their radiation resistance, ceramic materials are widely used as insulators in science and engineering and in nuclear-physical facilities.Previously, in studies of the radiation properties of SK-1 commercial steatite ceramic structural defects under highdose γ-irradiation (>10 7 Gy) were regarded as surface defects formed at the interface between a crystal (magnesium meta-silicate MgSiO 3 ) and glassy phases as a result of breaking of ≡Si-O-Mg bonds, under the polarizing action of magnesium cations, and the formation of ≡Si 3+ -O-Mg bonds [1][2][3][4].The present work studies the diffuse reflection spectra and the difference spectra (ΔR = R γ -R n-γ ) of irradiated SK-1 steatite ceramic.The conventional optical method based on studying optical absorption spectra is unsuited for most ceramic dielectrics. Even thin ceramic samples strongly absorb and scatter light. For this reason, diffuse reflection spectra, which in general are inversely proportional to the degree of absorption in the medium, can be used to evaluate the absorption. The diffuse reflection spectra of a ceramic were measured at wavelengths 200-700 nm on the apparatus whose block diagram is shown in Fig. 1.The apparatus is assembled around a SF-4A spectrophotometer and a PDO-1 diffuse reflection attachment. Depending on the wavelength range, FEU-39 and FEU-51 photomultipliers were used to detect the reflected light. The signal from the photomultiplier was fed into an M-95 microammeter. The passage scheme for the monochromatic light is as follows: the light 1 from the output slit of the monochromator strikes the PDO-1 rotary mirror 6, making a 45°angle with the optical axis of the monochromator, and then strikes at angle 90°the sample 2 or standard 3, which are placed on a PDO-1 rotary disk 4 and alternately positioned in the light beam. A PDO-1 conical mirror 5 collects the reflected light onto the photocathode of the photomultiplier. Unirradiated samples of SK-1 steatite ceramic (with the same reflection coefficient R as that of the experimental sample) were used as standards. The degree of reflection of the light was evaluated from the reflection coefficientwhere I irr and I unirr are the intensities of the light reflected from the irradiated and unirradiated samples, respectively.For measuring the diffuse reflection spectra, the wavelength resolution of the SF-4A spectrophotometer was 0.1-0.5 nm and the error in determining the diffuse reflection coefficient was 3-5%. The results were averaged over three samples. The samples were 1 mm thick, 10 × 10 mm plates as well as 15 mm in diameter and 2 mm thick disks. Their surface was ground with diamond power in order to attain the same surface diffusivity. The thickness was chosen so as to pre-

Extensive material has been accumulated in the last few years on radiation defects in dielectric materials based on oxides. Most ceramic dielectrics consist of simple or complex oxide compounds which comprise the crystalline and glassy phases of a ceramic [1]. The formation of structural defects in oxide compounds, such as AI203, MgO, and SiO 2, under the action of 6~ ",/-rays is unlikely, but it is possible under some conditions. For example, structural defects have been observed to form during low-energy electron irradiation of finely dispersed aluminum oxide [2]. As has already been mentioned, the ceramic materials are multiphase systems and possess a branching network of interfaces. The chemical bonds at the interfaces of the phases break, and for this reason defects accumulate at ,,he boundaries. The number of broken bonds will depend on the dispersity of the crystalline phase. These structural features of a ceramic can affect its radiation resistance. The objective of the present work was to study the characteristics of defect formation in steatite ceramic under a high 3,-ray dose.Experimental Procedure. The investigations were performed on SK-1 steatite ceramic, which has a fine-crystalline and uniform structure. The main phases of the ceramic are crystals of magnesium metasilicate (MgSiO3) and glass with a complex composition. The magnesium metasilicate crystals have an average grain size of 3-8 t~m and occupy 60-70% of the volume of the ceramic. Glass is distributed uniformly throughout the volume of the ceramic and surrounds the magnesium metasilicate grains [3]. Samples of SK-I ceramic were irradiated with 6~ "),-rays and neutrons from a VVR-SM reactor. The 9 ,/-ray dose was varied from 106 up to 2. I010 R, and the neutron fluence under reactor irradiation ranged from 1017 up to 1020 cm -2. Samples with dimensions of 10• and 10xl• mm were prepared for optical and ESR measurements, respectively. The ESR measurements were performed at room temperature in a Bruker (Germany) ESP-300 spectrometer. Magnesium oxide powder with a known concentration of Mn 2+ ions was used as a standard. The thermal luminescence of the samples was recorded with a FI~U-79 photomultiplier. The heating rate was equal to 5 deg/min.Results and Discussion. The investigations of the radiation-induced changes in the steatite ceramic [4, 5] showed that with a dose of 106-107 R the ceramic is colored as a result of accumulation of silicon dioxide in the pores. According to data from IR spectroscopy, petrography, and x-ray diffraction, the structure and phase composition of the ceramic materials remains unchanged, even at doses of 109 R and higher [6].Peaks with maxima at 115, 155, 220, and 275~ and a wide peak at temperatures above 350~ (Fig. 1) can be identified on the thermal luminescence curve of the irradiated ceramic. The thermal luminescence peak at 115~ in the case of a low dose is manifested in the form of an inflection on the low-temperature side at 155~ it reaches maximum intensity at a dose of 108 R and then the intensity dec...

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