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We studied optically induced effects in ultrafine Al2O3–BeO ceramics irradiated with a high-dose pulsed electron beam (130 keV). Upon optical excitation of ceramics at 470 nm, optically stimulated luminescence is observed due to the depletion of traps associated with thermoluminescence peaks at 380 and 530 K. These traps are characterized by a complex energy spectrum with a nonuniformly distributed photoionization cross section. The prospects of using optically stimulated luminescence of Al2O3–BeO ceramics in high-dose dosimetry (3–30 kGy) have been proved.

New features of isothermal build-up of thermally stimulated luminescence (TSL) related to deep traps in anion-deficient alumina single crystals are revealed. It was found that the TSL build-up at 630–750 K depends on the structure of the glow curve and is associated with the presence of a high-temperature component with T m = 700 K. Isothermal TSL build-up for the peak at 573 K is well expressed in UV-irradiated samples and is very weak after sample irradiation by a pulsed electron beam. The TSL build-up for this peak is registered for the luminescence of F centres but is absent for the emission of F 2 2+ centres and chromium ions. The obtained results confirm the validity of the kinetic model of the TSL build-up that takes into account the process of thermal ionization of the excited states of F centres in aluminum oxide. © 2019 Elsevier Ltd Eesti Teadusagentuur: IUT2-26, PUT PRG111 Russian Science Foundation, RSF: 18-72-10082 This work was financially supported by the Russian Science Foundation , project No. 18-72-10082 and Estonian Research Council , projects IUT2-26 and PUT PRG111 .

The luminescent and dosimetric properties of nanostructured aluminum oxide which contains a mixture of metastable transition Θ, δ, and κ-phases were investigated. To vary the phase composition of the samples, they were annealed in air at 850–1200 оС. It was found that annealing the samples at Т = 850–1100 оС in air results in a change in the percentages of κ- and δ-phases with a slight variation in the Θ-phase concentration. Alpha-phase begins to form in the samples at Т = 1100 оС, its concentration reaches 100% at Т = 1200 оС. The PCL spectra featured bands associated with F- and F2-type centers, the intensity of which decreased with increasing annealing temperature due to thermal destruction of centers. Kinetic TL parameters of the samples irradiated with a pulsed electron beam (130 keV) were found by deconvoluting TL curves into elementary peaks of general order kinetics. These parameters change insignificantly when the annealing temperature increases up to 1000 оС and they change greatly when the temperature grows further and α-phase is formed in the samples. The presence of sublinear sections of the TL dose response at doses of 1.5–45 kGy shows that the use of nanostructured aluminum oxide which contains transition phases for high-dose TL dosimetry of pulsed electron beams is promising.

New Al2O3–BeO ceramics were synthesized by using high-temperature treatment of the initial compacts of nanostructured alumina in BeO crucible. The decomposition of the pulsed cathodoluminescence spectra into Gaussians revealed the luminescence bands related to oxygen vacancies and their aggregates in the ceramics. TL of the synthesized ceramics exposed to high-dose irradiation contained three peaks at 360 (A), 525 (B) and 730 K (C). It was found that optical stimulation at the wavelength of 470 nm causes optical bleaching of the traps responsible for peaks A and B, in contrast to the deep traps of the peak C, and gives rise to OSL. At the same time, there was a shift of the position of peaks A and B to the high-temperature region. This result shows the presence of the energy distribution of the traps responsible for TL peak A. It was found that the range of linearity of the TL dose response after gamma-irradiation is from 0.01 to 1.0 kGy. After irradiation with a pulsed electron beam (130 keV), the linear behavior of the OSL dose response was observed from 3 to 30 kGy.

The effect of deep traps filled by a pulse electron beam on the thermoluminescent (TL) properties in Al2O3:C dosimetric crystals is studied. When the deep traps are filled, the dosimetric peak at 170 °C acquires a double-peak structure not present in the initial samples. The effect of the population of the deep centers having various nature (electron or hole traps) and energy depth on the shape of the dosimetric TL peak structure is analyzed. An assumption is made that in the temperature ranges of 350–500 °C and 650–750 °C, electron traps are emptied, whereas at T = 500–650 °C hole traps are emptied. The possibility of using the TL associated with deep traps in high-dose dosimetry of pulse electron beams is shown.

A mathematical model for calculation of the 90Sr absorbed doses in dental tissues is presented. The results of the Monte-Carlo calculations are compared to the data obtained by EPR measurements of dental tissues. Radiometric measurements of the 90Sr concentrations, TLD and EPR dosimetry investigations were performed in animal (dog) study. The importance of the irregular 90Sr distribution in the dentine for absorbed dose formation has been shown. The dominant dose formation factors (main source-tissues) were identified for the crown dentine and enamel. The model has shown agreement with experimental data which allows to determine further directions of the human tooth model development.