Thermoluminescence dosimetric properties of beryllium oxide

Beryllium oxide (BeO) displays strong thermoluminescence (TL) together with tissue - equivalent properties which underline its application as a TL dosimeter. In the dosimetry of X- and γ-rays some of the advantages of BeO over other TL materials are its commercial availability, low cost, chemical inertness, non-toxicity (as a ceramic), high sensitivity to ionizing radiations, good reproducibility of response, low fading, absence of low-temperature peaks and moderate energy dependence. Various authors have reported glow curves of BeO TL phosphor, whose dominant dosimetric peak lies between about 160 and 200 °C. The position of this peak, however, depends upon the type of the radiation used for exciting the phosphor. Although fading of TL is nominal when kept in the dark, the γ-exposed BeO phosphors fade faster when exposed to ambient light. When exposed to γ-radiation, these phosphors exhibit linearity from a minimum of about 1 mrad (1 rad =10-2 gray) up to approximately 10 rad, above which there is supralinear behaviour, and the concentration of impurity ions in BeO is reported to expand the linearity region. Ceramic samples have been reported to exhibit a roughly flat response when exposed to X-rays of 30–115 keV and γ-rays of 60Co. Because their response to thermal neutrons is negligible compared to the γ-response, the use of BeO has been suggested to measure the γ-component in the (n, γ) mixed fields. This revised version was published online in November 2006 with corrections to the Cover Date.     

Thermoluminescent and dosimetric properties of X ray phosphors

Rare earth doped oxide, phosphate, etc. are radioluminescent phosphors that have a broad application in X ray imaging, in luminescent screens, image transformers and in fluorescent lamp manufacturing. Some of them have interesting thermoluminescence features as well, which makes the phosphors applicable also in dosimetry. Two of these materials are Sr3(PO4)2 and BaFCl activated with europium. The general radioluminescence (RL) and thermoluminescence (TL) characteristics of these materials was investigated earlier and the preliminary results have already been published elsewhere. The aim of the present work is to investigate the interesting properties of these phosphors mainly from a dosimetric point of view (sensitivity, dose dependence, etc.).     

Gamma-ray dosimetric properties of molybdenum phosphate glasses

In the present work, a study of the temperature dependence of the d.c. electrical conductivity and conduction activation for a series of MoO₃-P₂O₃ glass systems has been carried out. The conductivity measurements of the unirradiated glass specimens proved to be mainly dependent on both temperature and transition metal ion content in the glass matrix. The results of the present investigation have shown that the conduction mechanism would be due to the electron exchange between the low and high valency states of the MoO₃ oxide (Mo" and Mo⁶⁺). The radiation-induced conductivity of the glass system studied, produced by gamma rays, has also been measured experimentally. The d.c. electrical conductivity has proved to be dose dependent, which showed a decrease with increasing -dose. The results reflect some evidence of the-ray dosimetric potential of the glass specimens studied.     

Optical images of dose distributions in Gel-Fricke: dosimetric performances of the gel

The purpose of this work was to examine the dosimetric performances of the radiochromic Fricke-Agarose-Xylenol Orange gel by optical measurements in order to perform dose reconstructions, in view of a future development for 3-D maps. Optical images and dose-response curves of the gel were obtained by a CCD-based device, originally designed for reading radiochromic films, that was modified to meet the optical properties of the dosemeter. With a resolution of 0.18 x 0.18 mm the optimum range of doses in which per cent uncertainty is lower than 2% was 3-10 Gy. The minimum detectable dose, estimated as the absorbed dose corresponding to 3 SD above background, was 0.1 Gy. With a resolution of 1.98 x 1.98 mm the optimum range of doses in which per cent uncertainty is lower than 2% was 0.3-10 Gy. The minimum detectable dose, estimated as the absorbed dose corresponding to 3 SD above background, was 0.015 Gy. The comparison with alanine dosemeters in the dose range 7-10 Gy showed agreement within a few per cent and the same agreement was observed for the comparison with TLD in the range 1-3 Gy.     

Thermal and mechanical properties of porous Y-PSZ/zircon composites

 The thermal and mechanical properties of sintered porous composites of yttria-partially-stabilized-zirconia (Y-PSZ) and zircon (ZrSiO₄) were investigated for a broad range of compositions. Fracture strengths of these composites were significantly improved with the zircon addition (0 to 50wt%). The addition of zircon also improved the thermal shock resistance. Specimens sintered at 1500^oC for 6 h with 15–20% porosity were shown to have superior strength and thermal shock resistance. These findings have been used in the manufacturing of ceramic permanent molds for brass casting. Received: 5 December 1997 / Accepted: 13 December 1997     

A review of the properties of the dosimetric systems and the quality assurance programmes of 48 dosimetric services in the European Union and Switzerland

This paper summarises the evaluation of the 1997 EURADOS questionnaire on dosimetric systems able to assess personal dose equivalent. In total, 56 approved dosimetric services in the European Union and Switzerland responded, together monitoring approximately 615,000 occupationally exposed persons. Of these services, 48 stated they were able to assess the external doses in terms of personal dose equivalent. The general aspects of the dosimetric systems and the quality assurance programmes of these services are discussed.     

Optical properties of nano-silicon

We investigated the optical properties of silicon clusters and Si nanocrystallites using photolumine-scence (PL) and Raman scattering technique. Broad luminescence band in the red region was observed from Si-doped SiO₂ thin films deposited by co-sputtering of Si and SiO₂ onp-type Si (100) substrates, annealed in Ar and O₂ atmosphere. Nanocrystalline Si particles fabricated by pulsed plasma processing technique showed infrared luminescence from as grown film at room temperature. Raman spectra from these films consisted of broad band superimposed on a sharp line near 516 cm⁻¹ whose intensity, frequency, and width depend on the particle sizes arising from the phonon confinement in the nanocrystalline silicon. We also performed PL, Raman and resonantly excited PL measurements on porous silicon film to compare the optical properties of Si nanostructures grown by different techniques. An extensive computer simulation using empirical pseudo-potential method was carried out for 5–18 atoms Si clusters and the calculated gap energies were close to our PL data. Paper presented at the 5th IUMRS ICA98, October 1998, Bangalore.     

Optical properties of interstellar medium

The spectra of normalized extinction of electromagnetic radiation by the interstellar medium have been analyzed in terms of a model representing the total extinction as a sum of three absorption coefficients. The first coefficient is related to optical transitions of the π-π* type and the second is related to those of the σ-σ* type in amorphous carbon. The third term represents two absorption features occurring in the region of the π-π* type transitions in the amorphous phase, which are satisfactorily described by the Gaussian contours peaked at 3.2 eV (385.6 nm) and 5.67 eV (217.5 nm). These contours are compared to published data on the absorption spectra of a copolymer composed of alternating triphenylamine and fluorene molecules. The results of this analysis confirm the hypothesis concerning the most probable chemical composition and physical state of particles of the interstellar medium.     

Optical properties of manganese films

The optical properties of thin manganese films in the thickness range 40 to 1200 nm are reported for UV, visible end near infrared regions. The reflectance and absorbance of annealed and unannealed manganese films is measured from film side and substrate side, in the wavelength range 190 to 900 no and for normal incidence of light. These measurements are used to calculate the refractive index (n), extinction coefficient (k), and the imaginary part of the dielectric constant ().     

Optical properties of polymer nanocomposites

Nanomaterials have emerged as an area of interest motivated by potential applications of these materials in light emitting diodes, solar cells, polarizers, light-stable colour filters, optical sensors, optical data communication and optical data storage. Nanomaterials are of particular interest as they combine the properties of two or more different materials with the possibility of possessing novel mechanical, electronic or chemical behaviour. Understanding and tuning such effects could lead to hybrid devices based on these nanocomposites with improved optical properties. We have prepared polymer nanocomposites of well-defined compositions and studied the optical properties of powders and their thin films. UV-vis absorption spectroscopy on nanocomposite powders and spectroscopic ellipsometry measurements on thin films was used to study the effect of interfacial morphology, interparticle spacing and finite size effects on optical properties of nanocomposites. Systematic shift in the imaginary part of the dielectric function can be seen with variation in size and fraction of the gold nanoparticle. The thickness of the film also plays a significant role in the tunability of the optical spectra.     

Optical properties of nanocrystalline ceria

We believe that, for the first time, the UV-visible optical reflectivity of nanocrystalline ceria with various particle sizes has been measured, and their optical absorption characteristics have been studied by Kramers-Kronig transformation. The wide absorption band in the 200-480-nm range consisted of two narrow bands. This wide band was designated as the charge transfer of O(2p)-Ce(4f) while both narrow bands, which overlapped in this wide band, were due to the well-known (2)F(5/2)-(2)F(7/2) spin-orbit splitting of the Ce 4f(1) state. With a decrease in the particle sizes of the samples, the bandwidth expanded distinctly and a red shift in the wide band was observed. On the other hand, the band gap between the narrow bands showed a remarkable increase. All of these phenomena resulted from the effects of quantum size and the interface of nanostructured materials.     

Optical properties of metal phthalocyanines

In this study, optical properties of phthalocyanines of five metals, i.e., cobalt, nickel, iron, copper, and manganese, have been discussed in the energy (E) range of 1.5–4.1 eV. Utilizing the available data of refractive index (n) and extinction coefficient (k) of these materials in the literature, the related optical properties such as the real (ε₁), imaginary (ε₂) parts of the complex dielectric constant (ε), and reflectivity (R) are calculated. Interpretations for the energies corresponding to the peaks in ε₂ are explained in terms of the Penn gap (E _P). High-frequency dielectric constant (ε_∞) values corresponding to four models, i.e., the conventional Lorentz model, modified Lorentz model, relaxed Lorentz model, and the dual Lorentz model are used to determine E _P. It is found that the E _P values corresponding to the conventional and dual Lorentz models are in good agreement with the average of energy peaks in the R-E and the ε₂-E spectra. The oscillator energy (E ₀) and the dispersion energy (E _d) of these materials have been determined utilizing the Wemple–DiDomenico model. The calculated values of (a) E ₀ are generally in good agreement with the Penn gap E _P, the average of the energy peaks in the R-E and the ε₂-E spectra and (b) E _d are comparable to those in the literature for CoPc and NiPc.     

Optical properties of ZnO nanostructures

We present a review of current research on the optical properties of ZnO nanostructures. We provide a brief introduction to different fabrication methods for various ZnO nanostructures and some general guidelines on how fabrication parameters (temperature, vapor-phase versus solution-phase deposition, etc.) affect their properties. A detailed discussion of photoluminescence, both in the UV region and in the visible spectral range, is provided. In addition, different gain (excitonic versus electron hole plasma) and feedback (random lasing versus individual nanostructures functioning as Fabry-Perot resonators) mechanisms for achieving stimulated emission are described. The factors affecting the achievement of stimulated emission are discussed, and the results of time-resolved studies of stimulated emission are summarized. Then, results of nonlinear optical studies, such as second-harmonic generation, are presented. Optical properties of doped ZnO nanostructures are also discussed, along with a concluding outlook for research into the optical properties of ZnO.     

Optical and electrical properties of quarternary chalcogenides

Optical and electrical characterizations have been made on four compounds of the type Cu₂ZnA^IVX₄^VI with A^IV = Si, Ge and X^VI = S, Se. These compounds belong to either a tetragonal superstructure of zincblende (stannite) or to an orthorhombic superstructure of wurtzite (wurtz-stannite) where a_or = 2a_w, b_or = a_w/tr3, and c_or = c_w. The electrical and optical properties are found to parallel the size of the group IV or group VI atom present.     

Optical and luminescent properties of ion-implanted films

It has been shown that band parameters for unimplanted films differ from those for bulk materials. Mechanical stresses and increased concentrations of defects seem to be responsible for this difference. The neighbourhood of the surface and the existence of drain paths for bulk defects determine the activity of the surface as a collector for mobile defects and hence their accumulation and their subsequent combination and annihilation reactions. From this point of view ion-implanted films with radiation-induced defects exhibit specific types of behaviour. For example, low energy ion bombardment (together with the removal of a very thin surface layer by etching) leads to an extensive movement of defects towards the surface and to a purification of the corresponding layer. In a number of cases even structural phase transformations take place within the surface layer, which lead in particular to the creation of surface excitons.High energy ion bombardment does not alter the band parameters of the films at the depth d of ion penetration but distorts the structure at the surface owing to a drain of defects into this layer. At the same time centres of scattering and radiative recombination are effectively induced at the depth d.     

Optical and magnetic properties of ZnCoO layers

Optical and magneto-optical properties of ZnCoO films grown at low temperature by Atomic Layer Deposition are discussed. Strong wide band absorption, with onset at about 2.4 eV, is observed in ZnCoO in addition to Co-related intra-shell transitions. This absorption band is related to Co 2+ to 3+ photo-ionization transition. A strong photoluminescence (PL) quenching is observed, which we relate to Co recharging in ZnO lattice. Mechanisms of PL quenching are discussed.     

ZnO纳米线的制备及其光学性能

采用物理热蒸发ZnS粉的方法,制备出了大规模的线状和棒状ZnO纳米结构.借助扫描电子显微镜、透射电子显微镜、激光拉曼光谱仪以及荧光光谱仪研究了ZnO纳米线的表面形貌、内部结构及其光学性能.结果表明,所得到的ZnO纳米线是六方的单晶结构,而且具有较好的发光性能和良好的结晶性.纳米线长约2～5μm,直径约60nm,其生长机制为气-固(VS)机制.     

Optical properties of polycrystalline films

We investigate the optical properties and intermolecular coupling of para-hexaphenyl polycrystalline films by site-selective spectroscopy, time-resolved photoluminescence and photoinduced absorption measurements. Our results point to (i) a short-range orientational and energetic disorder and (ii) the molecular character of the light emission, with no evidence of intermolecular excited states.