Action of a high dose ofγ-rays on steatite ceramic

Abstract

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...

Investigation of radiation defects in steatite ceramics SK-1 and SNC by the EPR method

“…A characteristic feature of steatite ceramics in comparison with other ceramic materials is its high mechanical strength and low dielectric losses in some materials, for example, high-aluminous materials as GB-7, UV-46, muliticcorundum M-23 [3,4]. In [5][6][7][8], we showed that in steatite ceramics SK-1, when exposed to high-dose γradiation (>10 9 R), radiation defects with high thermal stability are formed, which are observed as peaks of thermo-luminescence (TL), EPR spectra (signal with g=2.0012) and diffuse reflectance spectra (DR) (λ=220 nm). These defects are formed mainly in the crystalline phase of magnesium meta-silicate MgSiO 3 (nonstoichiometric MgSiO 3 ) or surface layers of grains of the crystalline phase with a defective structure formed.…”