V. Chernov

Thermoluminescence properties of ZnO and ZnO:Yb nanophosphors

ZnO and ZnO:Yb thermoluminescence nanophosphors have been developed and tested under beta radiation. Spherical nanoparticles of sizes ranging from 130to1200nm were prepared through a glycol mediated chemical synthesis. The Yb doping had a thermoluminescence quenching effect compared to undoped ZnO. The 5% Yb concentration produced a low fading, a single thermoluminescence glow peak structure, and a dose linearity behavior adequate for thermoluminescence dosimetry applications. The ZnO:Yb nanophosphor has a great potential as a dosimeter for monitoring in ionizing radiation fields.

Thermally and optically stimulated luminescence of new ZnO nanophosphors exposed to beta particle irradiation

In this work, we report on the thermoluminescence (TL) and the optically stimulated luminescence (OSL) of ZnO nanophosphors obtained by thermal annealing of ZnS powders synthesized by precipitation in a chemical bath deposition reaction. To obtain nanocrystalline ZnO, ZnS pellet-shaped samples were subjected to a sintering process at 700 °C during 24 h exposed to air at atmospheric pressure. Some samples were exposed to beta particles in the 0.15–10.15 kGy dose range and the integrated TL as a function of dose increased with dose level, with no saturation indication for the tested dose levels. Computerized glow-curve deconvolution of the experimental glow curves in individual peaks revealed a second-order kinetics. In order to test the OSL response, samples were irradiated with beta particles with doses up to 600 Gy, and an increasing intensity as dose increased was observed. We conclude that the new ZnO phosphors under investigation are good candidates to be used as dosimetric materials.

Dose rate effects on the thermoluminescence properties of MWCVD diamond films

Synthetic CVD diamond, being non-toxic and tissue equivalent, has been proposed as a ionizing radiation passive dosimeter with relevant applications in radiotherapy and clinical dosimetry. In the present work, the thermoluminescence (TL) properties of microwave-assisted chemical vapor deposition (MWCVD) diamond, 6 μm thick film grown on (100) silicon substrates, were studied after room temperature γ-irradiation for 2.4, 3.1, 5.94, 13.1, 20.67, 43.4 and 81.11 Gy min−1 dose rates in the range of 0.05–10 kGy. At fixed irradiation dose the TL efficiency increases as the dose rate increases. As the dose increases the peak temperature at the maximum intensity of the TL glow curve is shifted about 10 K degrees toward the lower temperature side. The TL glow curve shape resembles first-order kinetics for low-radiation doses and second-order kinetics for higher doses. Linear dose behavior was found for doses below 200 Gy and supralinear for higher doses; respectively, with a significant dependence on the dose rate, reaching saturation for higher doses around 2.0 kGy. Due to the dose rate dependence of the TL properties of the CVD diamond sample, it is necessary to take these effects into consideration for dosimetric applications involving synthetic CVD diamond.

Comparative investigations of TL and OSL in KCI:Eu2+ crystals irradiated with UV and X-rays

Abstract We present thermoluminescence (TL) glow curves and optical stimulated luminescence (OSL) response from both KCl:Eu2+ crystals irradiated with soft X-rays (20 KV, 80 μA) and ultraviolet light (230 nm). Two situations take place. First, we observed that for long time F-light bleaching (560 nm) the typical TL glow curve of X-rays irradiated KCl:Eu2+ resembles the TL glow curve of UV-irradiated samples. Second, along with OSL measurements, we have performed a thermal bleaching and we have addressed F and Fz participation in OSL. These results provide us a supportable correlation between F and Fz as responsible centers for OSL and TL processes.

Behaviour of F and Fz Centres Under Thermal Stimulation in KCl:Eu2☎ Irradiated with Ionizing and UV Radiation

The optical absorption (OA) of F and Fz, centres in beta-and UV-irradiated KCl: Eu2☎ have been studied. The spectra measured at room temperature and during the subsequent heatings up to 600 K, were analyzed by a deconvolution procedure. The OA bands of the F and Fz centres are well described respectively by asymmetric and symmetric gaussiane with parameters that are linearly dependent on the temperature. The thermal stability of the Fz centres correlates with the low-temperature thermostimulated luminescence (TL) peaks. The stability of the F centres is determined at least by two processes. Part of the F centres is destroyed together with the Fz centres. The remaining ones are destroyed during further heating up to 470 K, correlating with the TL peak at 425 K (at heating rate of 0.1 K/s).

Optical elements containing semitransparent wavelike films

Novel optical elements containing semitransparent wavelike films embedded into the bulk of transparent material, which form a reflection image without transmitted light distortion, are studied. The dynamic theory of light diffraction by a locally periodic multilayer semitransparent wavelike film is developed. A simple analytical formula for near Bragg diffraction order intensity is obtained for the case when only one diffraction order lies within the hologram angular selectivity. The phase modulation of light transmitted through the optical element containing wavelike films is estimated for single-layer and multilayer wavelike films with an arbitrary shape of surface. The restrictions on the structure parameters for which transmitted light distortions would be negligible are obtained. A new type of high-quality color hologram is proposed and shown to be feasible by calculation of hologram diffraction efficiency and spectral selectivity for three colors. Other possible applications, such as monochrome and color head-up and head-mounted displays, and imaging on spectacle lenses, are discussed.

3D Dynamic Thermography System for Biomedical Applications

3D thermography systems that combine 3D geometric data and 2D thermography data enable users to have a more accurate representation of the surface temperature distribution and aid in its interpretation. A system for 3D dynamic infrared thermography comprising two units is presented; each unit consists of an off-the-shelf depth camera rigidly mounted to a FLIR thermal camera. The units are fixed on the arms of the device that allow their placement in desired positions near the subject. To generate a single 3D thermogram, the data obtained from the depth cameras is registered with the images from the thermal cameras. The process of generating a 3D thermogram is repeated several times while thermally stimulating the surface of the subject to produce a series of 3D thermograms. The developed system provides a number of advantages in research for biomedical applications, such as the correct temperature measurements on curved surfaces, the possibility to select regions of interest by taking into account the shape of the subject and the possibility to use the 3D data to easily eliminate the background from 2D thermograms.

Analytical approximation of the nanoscale dose distribution in an irradiated medium with an embedded nanoparticle

In this work we propose an analytical approach describing the dose distribution around a NP embedded in a medium. The approach describes the following sequence of events: The homogenous and isotropic creation of secondary electrons under incident photon fluence; travel of the created electrons toward the NP surface and their escaping from the NP with different energies and angles; deposition of energy in surrounding medium. The radial dose distribution around the NP was found as the average energy deposited by the escaped electrons in a spherical shell at a distance r from the NP center normalized to its mass. The continuous slowing down approximation and the assumption that created electrons travel in a straight-line path were used. As result, a set of analytical expressions describing the dose distribution was derived. The expressions were applied to the calculation of the dose distribution around spherical gold NPs of different size embedded in water. It was shown that the dose distribution is close to the 1/r2 dependence and practically independent of the NP radius.

Multilayer optical disk and method of its management for preventing its illegal use

The special shape of the optical disk tracking grooves is proposed. These tracking grooves are similar to the blazed diffraction grating grooves. The grooves structure can be read by the standard optical disk reading equipment. The multilayer optical disk with slant tracking grooves is proposed. These grooves have different planes and angles of inclination for different data layers. This allows to direct the signals reflected from the different data layers to the different photodetectors. The optical disk capacity increases due to excluding space between tracking grooves and due to increasing the number of data layers. Sequential and parallel optical disk reading options are possible. The technique of information pits arrangement is proposed for parallel reading of information from several data layers. For protecting of the optical disk against its illegal use the disk is made partly recordable and an initialization procedure is performed at the users recording/reproducing device. During the initialization procedure identifying parameters of the users device are recorded onto recordable layer of the disk. Also, the unique combination of the bits pairs containing both information prerecorded on the optical disk and information about the users recording/reproducing device is remembered in the special flash memory of the users device.

Nanoscale dose deposition in cell structures under X-ray irradiation treatment assisted with nanoparticles: An analytical approach to the relative biological effectiveness

In this study, an analytical model for the assessment of the modification of cell culture survival under ionizing radiation assisted with nanoparticles (NPs) is presented. The model starts from the radial dose deposition around a single NP, which is used to describe the dose deposition in a cell structure with embedded NPs and, in turn, to evaluate the number of lesions formed by ionizing radiation. The model is applied to the calculation of relative biological effectiveness values for cells exposed to 0.5mg/g of uniformly dispersed NPs with a radius of 10nm made of Fe, I, Gd, Hf, Pt and Au and irradiated with X-rays of energies 20keV higher than the element K-shell binding energy.