Table of contents

These proceedings represent a sample of the scientific works presented during ICDIM2008, the 16th International Conference on Defects in Insulating Materials, held at the Federal University of Sergipe, Aracaju, Brazil from 24–29 August 2008. The conference was the latest in a series which began at Argonne in 1956, and which has been held most recently in Riga, Latvia (2004) and Johannesburg, South Africa (2000). The conference was also related scientifically to the EURODIM series, which have been held most recently in Milan, Italy (2006), Wroclaw, Poland (2002) and Pecs, Hungary (2010).

The aim of the conference was to bring together physicists, chemists and materials scientist to discuss defects in insulating materials and their effect on materials, including their optical, mass/charge transport, energy storage and sensor properties. The conference featured 6 plenary lectures, 60 contributed lectures and about 130 posters. The posters were displayed for the whole conference, but discussed in two three-hour sessions.

We are grateful to the International Advisory Committee for suggesting invited speakers and to the Programme Committee for their help in refereeing all the abstracts and choosing the contributed oral contributions. We would also like to thank the Local Organising Committee and the Brazilian Physical Society for their help with local organisation and the online registration/payment process respectively. The chairpersons would like to specially thanks all the sponsors listed below for financial support.

The Federal University of Sergipe, one of the public and 'free tuition' Universities of the Country, run by the Brazilian Ministry of Education, were pleased to host this 16th meeting, the first one in Latin America.

Mario E G ValerioConference ChairRobert A JacksonProgramme Chair

Conference Scope

Scope of the Conference was the presentation of the latest investigations on point and extended defects in bulk materials and thin films. Technological applications will be presented alongside fundamental measurements and theories.

The main scientific areas included:

1 Fundamental physical phenomena Point and extended defects in wide band-gap systems: oxides, fluorides, nitrides, alkali- and silver-halides, perovskites, minerals, ceramics, nano-structures, organic molecular crystals, glasses, high-k and low-k materials, photonic crystals.

2 Defects at surfaces and interfaces Thin films and low-dimensional systems. Colloids, nano-crystals, and aggregates. Defects and material preparation technology. Defects modelling and computational methods. Radiation effects, radiation induced defects, colour centres. Luminescence of excitons, impurities, and defects. Electronic excitations, excited state dynamics, radiative and non-radiative relaxations. Scintillation, energy transfer and storage, carrier trapping phenomena. Non-linear optical phenomena. Laser active centres. Phonons and defects, electron–phonon interactions. Defect diffusion, ionic relaxations, ionic transport.

3 Technological applications Radiologic imaging and detection, scintillators, and dosimeters. Optical devices and photonics, photorefractive electro-optics, optical fibres, lasers. Materials for micro-electronics. Solid electrolytes, fuel cells, electrochemical sensors, fast ionic conductors.

Conference chairpersons: Mário E G Valerio (Conference Chairman), Physics Department, Federal University of Sergipe, SE, Brasil Robert A Jackson (Programme Chairman), School of Physical and Geographical Sciences, Keele University, Keele, UK

Conference committees:International Advisory Committee R Capelletti, Italy A V Chadwick, UK J Corish, Ireland J D Comins, South Africa H W den Hartog, The Netherlands K Funke, Germany Robert A Jackson, UK O Kanert, Germany A A Kaplyanskii, Russia A Lushchik, Estonia F Lüty, USA M Moreno, Spain P E Ngoepe, South Africa M Nikl, Czech Republic S V Nistor, Romania Ch Pedrini, France O F Schirmer, Germany J-M Spaeth, Germany A M Stoneham, UK M Suszynska, Poland I Tale, Latvia M E G Valerio, Brasil R T Williams, USA

Programme Committee Robert A Jackson (Chair), University of Keele, UK R M Montereali, ENEA C.R. Frascati, Rome, Italy M Moreno, University of Cantabria, Spain Ch Pedrini, University Lyon, France Klaus W H Krambrock, UFMG, MG, Brasil Volkmar Dierolf, Lehigh University, USA Laszlo Kovács, Hungarian Academy of Sciences, Hungary M E G Valerio, UFS, SE, Brasil

Local Organizing Committee M E G Valerio, UFS, SE, Brasil Sonia L Baldochi, IPEN, SP, Brasil Klaus W H Krambrock, UFMG, MG, Brasil Livio Amaral, UFRGS, RS, Brasil Ana R Blak, USP, SP, Brasil Marco Cremona, PUC-RJ, RJ, Brasil Anderson S L Gomes, UFPE, PE, Brasil Spero Penha Morato, LaserTools, SP, Brasil Alejandro Ayala, UFC, CE, Brasil

ICDIM2008 Sponsors:

All papers published in this volume of Journal of Physics: Conference Series have been peer reviewed through processes administered by the proceedings Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

Luminescence characteristics and creation of (WO₄)³⁻ and (WO₄)³⁻-A³⁺ centers were studied in PbWO₄ crystals doped with trivalent rare-earth A³⁺ ions (A³⁺: La³⁺, Lu³⁺, Y³⁺, Ce³⁺, Gd³⁺, Eu³⁺) under selective irradiation in the 3.4-5.0 eV energy range at 5–80 K. Optically created centers were detected by the TSL and ESR methods. Creation spectra of the mentioned centers were measured and the activation energies needed for their creation were calculated. It was found that both the (WO₄)³⁻and (WO₄)³⁻-A³⁺ centers can be created not only in the band-to-band transitions region but also in the 3.8 ± 0.4 eV range. The activation energy for their creation at T<40 K is close to zero. Under irradiation in the energy range around 3.8 eV at T>60 K, the activation energy for (WO₄)³⁻-A³⁺ centers creation varies from 10 to 25 meV, depending on the irradiation energy. A new UV emission, peaking in the 3.05–3.20 eV range, was found whose thermal quenching takes place with the same activation energy. Radiative decay of defect-related states, as well as the processes of their non-radiative decay, resulting in creation of (WO₄)³⁻-A³⁺ centers and thermal quenching of the UV emission, are considered to explain the effects observed.

The γ-coloured Lithium Fluoride crystals visible fluorescence at room temperature was measured under excitation with ultra-violet continuous wave light at λ = 244 nm from a frequency-doubled Ar⁺-ion laser. The excitation wavelength lies close to the peak of the F-centre absorption band for LiF, and the visible luminescence spectrum consists of two broad emission bands, assigned to F⁺₃ and F₂ centres in LiF. The luminescence spectrum changes in a short time after start of illumination. The main effect of 244 nm laser illumination is the observed change in the F₂ emission band intensity, which is strongly and permanently bleached by the CW UV light at 244 nm as soon as it illuminates the crystal. The time evolution of the fluorescence signals can be measured, and the corresponding curves were fitted by a single exponential decay, resulting in characteristic time constants of ≈ 9 s and ≈ 30 s for the F₂ and F⁺₃ bands, respectively. The reported effects support previous work about UV laser illumination in the F-band absorption peak as an effective method to control the ratio of F₂ to F⁺₃ centres in LiF, due to permanent bleaching of the former ones.

Stable formation of primary F and aggregate F₂ and F₃⁺ colour centres in LiF crystals irradiated with a X-ray table-top source was investigated by optical absorption and photoluminescence measurements as a function of the irradiation dose. The F absorption band intensity follows a power law behaviour as a function of dose with a single exponent equal to 0.77, a value in excellent agreement with the predictions of a unified model for colour centres formation. The aggregate defects photoluminescence response appears suitable for applications in high dynamic range imaging plate X-ray detectors based on photoluminescence of coloured LiF. The choice of polycrystalline LiF thin films grown on different substrates allows one to obtain high resolved images even when more penetrating X-rays are used, as the colour centres formation is limited in depth by the film total thickness.

The concentrations of primary F centres and F₂ and F₃⁺ aggregate defects were evaluated as a function of the irradiation dose in broad-band light-emitting single-mode strip waveguides directly written with 12 keV electrons at the surface of a LiF crystal. From a careful best-fit procedure of the optical transmission spectra, measured on microstructures only few tens of micrometers wide, the spectral contributions of several types of colour centres were identified and quantified. This characterization provided useful information for the optimization of these confining microstructures and for the development of waveguide colour centre lasers.

Photoluminescence and photo-excited conductivity data as well as structural analysis are presented for sol-gel SnO₂ thin films doped with rare earth ions Eu³⁺ and Er³⁺, deposited by sol-gel-dip-coating technique. Photoluminescence spectra are obtained under excitation with various types of monochromatic light sources, such as Kr⁺, Ar⁺ and Nd:YAG lasers, besides a Xe lamp plus a selective monochromator with UV grating. The luminescence fine structure is rather different depending on the location of the rare-earth doping, at lattice symmetric sites or segregated at the asymmetric grain boundary layer sites. The decay of photo-excited conductivity also shows different trapping rate depending on the rare-earth concentration. For Er-doped films, above the saturation limit, the evaluated capture energy is higher than for films with concentration below the limit, in good agreement with the different behaviour obtained from luminescence data. For Eu-doped films, the difference in the capture energy is not so evident in these materials with nanoscocopic crystallites, even though the luminescence spectra are rather distinct. It seems that grain boundary scattering plays a major role in Eu-doped SnO₂ films. Structural evaluation helps to interpret the electro-optical data.

The energy-dependent pseudopotentials for electron-excess color centers in ionic crystals adopted by Bartram, Stoneham and Gash (BSG) were determined by a smoothness criterion because the trial wave functions employed are slowly varying on the scale of the ion cores. Energy-independent norm-conserving pseudopotentials were introduced subsequently in the context of molecular-orbital calculations to ensure that the outer parts of valence pseudo-orbitals coincide with those of true valence orbitals. In the present investigation, whole-ion norm-conserving pseudopotentials calculated from numerical wave functions are employed in F-center calculations for comparison with BSG calculations. It is concluded that the smoothness criterion should take precedence in that application.

A samarium doped polycrystalline ZrO₂ bulk sample was investigated for its phase composition as well as optical properties within the temperature range 6–300 K. From micro-Raman measurements the existence of tetragonal as well as monoclinic phase was confirmed. The emission spectrum of Sm³⁺ reveals drastic changes under excitation near the region of fundamental absorption. Combined excitation-emission spectroscopy (CEES) measurements reveal three different sites for the dopant ions to be present in the sample. Nature and excitation scheme of the three sites are discussed.

The incorporation site of Cu in the scintillator and thermoluminescent dosimeter material lithium tetraborate Li₂B₄O₇:Cu has been shown to depend on the charge state of the dopant. As confirmed by a refined analysis, the EPR spectra of an unpaired hole can be ascribed to Cu²⁺ situated near the Li lattice site with C₁ symmetry, in contrast to the higher (C₂) overall symmetry reported earlier for Cu⁺ in its relaxed excited state, the latter suggesting interstitial incorporation for the monovalent dopant. Consequences for charge transfer processes involving copper ions are discussed.

LiF is a nonhygroscopic alkali halide crystal which possesses good optical and physical properties, and can host different species of colour centres at room temperature. Colour centres in LiF present broad absorption and emission bands in the near UV, visible and near IR regions of the spectrum. In this paper we study spectroscopic properties of colour centres produced in LiF by ultrashort laser pulses. The absorption and emission properties of these materials were measured showing that during the irradiation F, F₂, F₂⁺, F₃⁺ and F₂⁻ colour centres were created in the crystals. A colour centres formation dose-like curve as a function of the ultrashort pulse energy was determined using fluorescence spectroscopy.

In this work we present the spectroscopic properties of KY3F10 (KY3F) single crystals doped with thulium and also co-doped with ytterbium and/or neodymium, KY3F:Yb:Nd:Tm and KY3F:Nd:Tm. The most important processes that lead to the thulium up conversion emissions were identified. The absorption spectra of the samples were measured at room temperature in the range of 200 nm-1200 nm. The emission spectra were obtained by exciting the samples with a 797 nm laser diode and were analyzed using a lock-in amplifier technique. A time-resolved luminescence spectroscopy technique was employed to measure the luminescence decays and to determine the mechanisms involved in the energy transfer up-conversion processes. Analysis of the energy transfer processes dynamics in KY3F:Yb:Tm:Nd crystal, using selective pulsed-laser excitations, shows that the energy transfer from Nd3+ to Yb3+ ions is the mechanism responsible for the enhancement of the blue up-conversion efficiency when compared with the Yb:Tm system. In the case of KY3F:Nd:Tm it is observed emissions at 350, 355 and 452 nm excited by an additional Yb:Tm step cross relaxation, Yb (2F5/2) : Tm (1G4) that populates the 1D2 (Tm3+) excited level. A study of the energy transfer processes in KY3F:Yb:Tm:Nd crystal showed that the 1G4 excited level is mainly populated by the sequence of two nonradiative energy processes that starts well after the Nd3+ and Tm3+ excitation at 797nm: Nd (4F3/2) → Yb (2F7/2) followed by Yb (2F5/2) → Tm (3H4) → Tm (1G4).

Ferroelectric materials such as lithium niobate (LiNbO₃) and the isostructural lithium tantalate (LiTaO₃) play an important role in integrated optics since they allow the possibility to combine their favourable electro-optical, acousto-optical, and nonlinear properties with the ability to add additional functional groups by doping. Examples are rare earth ions that act as active centres for laser and optical amplifier applications. We present our sites-selective spectroscopic studies on Er³⁺ doped nearly stoichiometric LiTaO₃ that include results about the assignment of excitation and emission peaks to different sites, symmetry properties of these sites, energy transfer among major sites, and up-conversion efficiencies. We compare the results in LiTiO₃ with the corresponding ones in the much better studied LiNbO₃ host and find that the type of centres and their spectral feature are very similar.

Biocompatible phosphate materials are used in different applications like bone and dental implants, drug delivery systems and others, but could also be applied in inorganic sunscreens. Using sunscreens is extremely necessary, because long time exposure to sun can cause skin cancer. In this work chemical precipitation method has been used to produce hydroxyapatite. Cr³⁺, Zn²⁺ and Fe³⁺ doped samples were characterized using powder X-Ray Diffraction (XRD) and Optical Absorption techniques. X-ray diffraction measurements confirmed the materials were in the expected crystalline structures. The crystallite size as measured from the X-ray pattern was 23–27 nm (±1). The absorption spectra in the ultraviolet and visible ranges indicate that appropriately doped and sized hydroxyapatite particles may have potential applications as active constituents of sunscreens.

This work investigates the thermoluminescent (TL) dosimetric properties in natural spodumene, LiAlSi₂O₆, called kunzite, from Minas Gerais State, Brazil. The mineralogical and chemical composition of this material was identified by means X-ray fluorescence and X-ray diffraction. Some dosimetric properties were studied, such as thermoluminescent emission curves as function of gamma dose. The glow curves of annealed kunzite presented two very intense TL peaks at 215 °C (peak II) and 350 °C (peak III), after gamma irradiation, being both of first kinetic order. These two most prominent peaks analyzed do not presented a linear growth in the range of 50 to 5000 Gy in the range of doses studied. The peak II also presented a very short calculated lifetime, which means it is hardly can be used in dosimetry, while the peak III has a longer lifetime and could be used in some applications for high doses dosimetry.

Combined radioluminescence, afterglow and thermoluminescence experiments on single-crystal samples of co-doped CsI:Tl,Sm suggest that deeper samarium electron traps scavenge electrons from shallower thallium traps and that electrons subsequently released by samarium recombine non-radiatively with holes trapped as V_KA(Tl⁺) centers, thus providing a mechanism for suppression of trapped-charge accumulation in repetitive applications. In the present investigation, experiments performed on two single-crystal samples of CsI:Tl,Sm with nominal concentrations of 0.11% Tl⁺ and of 0.2% and 0.05% Sm²⁺, respectively, support the inference that electrons tunnel freely between samarium ions and are trapped preferentially near V_KA(Tl⁺) centers where non-radiative recombination is the rate-limiting step.

Single crystal film of Tb₃Al₅O₁₂:Mn, with concentration of Mn approximately equal to 0.07 at%, has been grown by liquid phase epitaxy on Y₃Al₅O₁₂ substrate. We have measured the absorption, luminescence, luminescence excitation spectra and luminescence kinetics of the film. To analyze the energetic structure and to estimate the crystal field strength we have measured the photoluminescence spectra under high hydrostatic pressure applied in diamond anvil cell up to 110 kbar. The Mn emission was consisted with the band peaked at 16800 cm⁻¹ that shifts toward the lower energy with increasing pressure with the rate −9 cm⁻¹/kbar. To characterize the Mn charge state we performed calculations of Tanabe -Sugano diagrams for 3d⁵, 3d⁴ and 3d³ system. The negative pressure shift of the 16800 cm⁻¹ band yields attribution of this band to the ⁴T₁ →⁶A₁ transition in dodecahedrally coordinated Mn²⁺ ion. We have estimated quantity of Dq/B equal to 1.8 ±0.2. The configurational coordinate diagram of the Mn²⁺(3d⁵) has been calculated to analyze the nonradiative deexcitation processes ⁴T₁ → ²T₂ →⁶A₁.

A number of investigations have shown that the thermal conductivity of alkali halide crystals is markedly affected by crystalline defects, chiefly in the low temperature region, say below around 10 K. The effects are very prominent after plastic deformation, where the conductivity is reduced by more than a factor of 10 after deformation by several percent already. Albeit a considerable amount of data and respective models have been elaborated, the correspondence between models and the body of experimental results still needs improvement, especially in the temperature range between around 1 and 5 K. As will be shown for the case of NaCl, where most of the experimental results exist, a satisfactory description of the thermal conductivity properties can be obtained when relying on, instead of dislocations and/or vacancy defects, a debris defect as suggested by transmission electron microscopy.

The fine structure (FS) accompanying a few lines, originated by crystal field (CF) transitions of rare earths (RE), as Er³⁺ and Tm³⁺, in BaY₂F₈ single crystals, is analyzed as a function of the RE³⁺ concentration (0.5÷20 at%) and temperature (9-300 K), by using high resolution (as fine as 0.02 cm⁻¹) Fourier transform spectroscopy and linear dichroism measurements. The 9 K absorption spectra show that FS includes weak, narrow, and closely spaced (0.4÷0.8 cm⁻¹) lines, covering a few cm⁻¹ range on both sides of the narrowest among the CF lines. The FS increases by increasing the RE³⁺ concentration and vanishes at rather low temperature (40 and 60 K for Er³⁺ and Tm³⁺, respectively). The polarized light spectra confirm the association of a given set of FS lines to a specific CF line. The FS is ascribed to the simultaneous excitation of an electronic CF transition and of a local librational (or hindered rotation) mode of the RE³⁺-F⁻ group. The attribution is supported 1) by specific features of the host matrix and guest rare earths, which allow some mobility of F⁻ ions, and 2) by the spacing of the FS lines, which is in excellent agreement with the calculated RE³⁺-F⁻ group rotational constant.

Photo- and thermo-luminescence techniques are applied to several kinds of single crystal complex oxide scintillators to reveal tunnelling-driven radiative recombination processes. The tunnelling mechanism provides the physical ground to interpret the observed luminescence and scintillation characteristics which could not be explained by classical radiative recombination schemes.

We studied oxyfluoride composites based on lithium silicate glasses with yttrium fluorides and rare-earth dopants. The electron paramagnetic resonance (EPR) has been used to obtain information about radiation induced defects in these materials. Spectra have been measured before and after X-ray irradiation at room temperature and at liquid nitrogen temperature. Fluoride crystallites within samples were created by means of thermal treatment at specific temperatures. EPR spectra of radiation induced defects in oxyfluoride glass ceramics, in which crystallites have not been yet created, show no explicit hfs interaction of fluorine nuclei. However, in glass ceramics, which already contains fluoride crystallites, the hfs characteristic to fluorine nuclei appears in the EPR spectra. EPR hyperfine structure could be explained within a model of an F-type centre in YF₃ crystalline phase.

We have studied the growth and properties of the Ce³⁺ - doped epitaxial garnet films. The single crystalline films were prepared by liquid phase epitaxy. Various fluxes were used with the goal to reduce the flux-related impurities, which could have a negative influence on the optical and scintillation properties. Crystallographic properties, film morphology and emission properties were studied in detail.

Nowadays, the three dimensional (3D) dosimetry has been studied by many researchers for application in radiotherapy and radiosurgery treatments, because this kind of dosimeter enable to evaluate the 3D dose distribution. The alanine gel dosimeter was developed at IPEN to be applied to 3D dose evaluations using magnetic resonance imaging. This dosimeter is a gel material based on the transformation of the ferrous ions in ferric ions, which presents significant improvement on previous alanine systems developed by Costa (1994). The DL-Alanine (C₃H₇NO₂) is an amino acid tissue equivalent that improves the production of ferric ions in the solution. The ferric ions concentration can be measured by spectrophometry technique. This work aims to analyse the stability and influence of the dose rate in the optical signal response of alanine gel dosimeter, since these two properties are very important for characterization and standardization of any dosimeter.

Sodalite, Na₈Al₆Si₆O₂₄Cl₂, a natural silicate mineral, has been investigated concerning its thermoluminescence (TL) and electron paramagnetic resonance (EPR) properties. Samples, both natural and heat treated at 500°C for 30min, present an EPR signal at g=2.01132. The irradiation induces two signals at g=2.0008 and a group of 11 lines due to an O⁻ ion in an intermediate position with respect to two adjacent Al nuclei, that are superimposed on the signal at g=2.0008. An annealing at 500 °C/30min produces a broad signal around g~2.0, probably due to Fe³⁺ magnetic dipole interactions. The samples were annealed at 500 °C/30min and then irradiated with gamma-ray doses varying from 1 Gy to 20 kGy. All the samples have shown TL peaks at 110, 230 and 270 °C. Similar results were obtained for natural samples. The accumulated dose (AD) was determined to be AD~2.5 kGy and the annual dose of (0.595±0.001) mGy/year was obtained from the concentration of U, Th, and K₂O in the sample. Therefore, the age obtained for natural sodalite was (4.2±0.2)10⁶ years.

Pellets of lizardite crystals (Mg₃ [Si,Fe]₂O₅ (OH)₄]) and teflon powder have been investigated to identify the centers related to thermoluminescence (TL) emission. All the Tl peaks are well fitted by using a second order kinetic model and the related trap parameters and activation energy are evaluated. Moreover, the measured optical absorption bands, in the visible and UV ranges, and in the infrared region, are attributed to charge transfer involving Mn and Fe ions and to vibration modes of Mg-O-H groups, respectively

Effects of monochromatic UV radiation on the thermoluminescence glow curve of annealed KBr:Cu crystals have been studied at low temperature. The crystals were irradiated at 20K and heated up to 300K at a rate of 0.1Ks⁻¹, approximately. For all the irradiation wavelengths used, the glow curves consist of two peaks around 170 and 270K. Their intensities have been observed to depend on the wavelength of irradiation. Both emissions resulted to be more intense when the irradiation wavelengths was near the absorption peak of the Cu⁺ ion or near the band to band absorption of CuBr. Their intensities increase with increasing annealing time. The results are explained in terms of the formation of CuBr nanoparticles during the annealing treatment. The thermally stimulated recombination luminescence appears to be associated to the 3d⁹4s-3d¹⁰ transitions of the Cu⁺ ion. So two possible mechanisms of the e-h pair formation could be used to explain the results: ionization of Cu⁺, Cu⁺ → Cu²⁺ + e, or ionization of halogen ions that are within the CuBr as B → Br⁰ + e. In the first case, the recombination luminescence is obtained from the trapping of electrons by the Cu²⁺ ions, while in the second case, the e-h recombination energy would be transferred to the Cu⁺ ions.

This paper presents the preparation method and the thermoluminescence analysis of aluminium oxide doped with Tb³⁺ and Tb³⁺-Mg²⁺ obtained by Combustion Synthesis (CS). An aqueous solution containing stoichiometric amounts of aluminium, terbium, magnesium nitrates and urea were mixed and introduced in a muffle furnace pre-heated to 500°C. After combustion, the samples were thermally treated at 1300°C and irradiated with a Co-60 gamma radiation source. The TL glow curves of the annealed Al₂O₃:Tb and Al₂O₃:Tb,Mg samples presented a well defined TL peak at approximately 200 °C, whereas the samples without heat-treatment presented a large number of TL peaks in the range from 150 to 500°C. These peaks were attributed to amorphous and phase impurities (γ-Al₂O₃ mixed with the α-phase) still present in the sample. Dose response analysis showed a linear response in the dose range from 0.5 to 5 Gy. These results strongly suggest that CS is a suitable technique to prepare doped aluminium oxide for TL dosimetric applications.

The present work shows a detailed study of the effects of preheating in ESR signals of four alkaline feldspar samples. ESR results showed Fe³⁺, Al-O⁻Al, Ti³⁺ and [Pb-Pb]³⁺ centers, When the samples were gamma-irradiated, the concentration of the Fe³⁺ centers deceased in all the samples, but the Al-O -Al center concentration increased after about 50 Gy while that of the Ti³⁺ and [Pb-Pb]³⁺ centres became almost constant. The effects of preheating were observed in samples previously irradiated with doses of 0.2 and 3 kGy after heating at 100, 200, 300 and 400 ºC, respectively for 10 minutes. In the orthoclase sample FELW, the Fe³⁺ signal remained almost constant up to 300 ºC and increased at 400 ºC, while that of the Al center decreased slowly between 100 and 300 ºC, but increased at 400 ºC. In the microcline sample FELG an increase of the Al coupled with [TiO4]" centres was observed up to 300 ºC, while a decrease occurred for higher temperatures. Fe³⁺ center concentration increased up to 200 ºC and became nearly constant for higher temperatures. According to our results, even preheating at temperatures as low as 200 ºC can change the concentration of Fe, Al and Ti centers in the sample; this fact can modify the luminescence response of the samples with the dose, because all these centers are associated with one or more emission spectra bands.

The aim of this study is to investigate the effect of particle size in the thermoluminescence (TL) response of natural quartz sensitized with high gamma dose. For this, fragments of a single crystal taken from the Solonópole district (Brazil) were crushed and classified into ten size fractions ranging from 38 μm to 5 mm. Aliquots of each size fraction were sensitized with 25 kGy of gamma dose of ⁶⁰Co and heat-treated in a muffle furnace at 400^oC. The non-sensitized samples were exposed to test doses between 50 Gy and 5 kGy and the sensitized samples were exposed to a unique test dose equal to 50 mGy. For non-sensitized samples, the TL peak near 325 °C increases with the particle size decreasing. However, in the case of sensitized samples, the TL output near 280 °C increases with the increasing of particle size up to mean grain size equal to 308 μm. Above 308 μm, an abrupt reduction in the TL intensity was noticed. These effects are discussed in relation to the specific surface area and the different interaction of high gamma doses with fine and coarse particles of quartz.

The aim of this study is to investigate the thermoluminescence (TL) and infrared-stimulated luminescence (IRSL) properties of three types of feldspars from the districts of Solonópole and Parelhas located in the Northeast region of Brazil in order to propose a preheat procedure to minimize the anomalous fading effect in these materials. The feldspar samples were characterized by X-ray diffraction (XRD) and X-ray fluorescence spectrometry (XRF). The XRD analysis showed that the feldspar from Solonópole and one of the samples from the Parelhas district were classified as microcline (K-feldspar). The other sample from Parelhas was classified as albite (Na-feldspar) mixed with low concentration of muscovite and quartz. Studies of the fading effects in TL and IRSL signals for 30 days and preheating effects from 50 to 250°C for 10 minutes were carried out with these samples. The results show that preheating at 125°C is sufficient to avoid the 30 days fading. The TL and IRSL dose responses for ⁶⁰Co gamma radiation were studied in the range of 1 to 400 Gy. The results showed a linear response in the range of 1 to 100 Gy for the two types of Parelhas feldspars and from 50 to 400 Gy for the Solonópole feldspar. The low sensitivity showed by the feldspar from Solonópole is discussed in relation to its mineralogical composition. It is concluded that the TL and IRSL sensitivities are not associated with K- and Na- types of feldspar. The results of this paper will contribute to a standardized moderate annealing treatment for retrospective dosimetry and dating.

To study the doses received by patient submitted to ionizing radiation, several materials are used to simulate the human tissue and organs. The total mass attenuation coefficient is a reasonable way for evaluating the usage in dosimetry of these materials. The total mass attenuation coefficient is determined by photon energy and constituent elements of the material. Currently, the human phantoms are composed by a unique material that presents characteristics similar to the mean proprieties of the different tissues within the region. Therefore, the phantoms are usually homogeneous and filled with a material similar to soft tissue. We studied ten materials used as soft tissue-simulating. These materials were named: bolus, nylon^®, orange articulation wax, red articulation wax, PMMA, modelling clay, bee wax, paraffin 1, paraffin 2 and pitch. The objective of this study was to verify the best material to simulate the human cerebral tissue. We determined the elementary composition, mass density and, therefore, calculated the total mass attenuation coefficient of each material. The results were compared to the values established by the International Commission on Radiation Units and Measurements - ICRU, report n° 44, and by the International Commission on Radiation Protection - ICRP, report n° 89, to determine the best material for this energy interval. These results indicate that new head phantoms can be constructed with nylon^®.

LiF with different dopants has been one of the most investigated materials to use as thermoluminescent dosimeter. Even so, in a previous work we observed that pellets produced with pure LiF have applicability to ionizing radiation dosimetry, showing dosimetric peaks in temperatures high enough to overcome most of fading problems. In this work we studied the thermoluminescent properties of pellets prepared with LiF and unusual dopants. As dopants were tested rare earth metals like europium, terbium, dysprosium and neodymium. The more intense TL response was showed by samples doped with Nd. Although they are bluish due to presence of the Nd, the pellets produced with LiF:Nd exhibited a TL emission two times more intense than the one in pure LiF.

The use of thermoluminescence (TL) is very useful for application in retrospective dosimetry, that is, for inference of the dose of radiation undergone for some material. The calculation of the lifetime of TL peaks can help to clarify which TL intensity is due to the dose of environmental radiation and which is proceeding from the accident with radiation. In this work, the kinetic order (b), activation energy (Et) and the frequency factor (s) were obtained for quartz samples that had been extracted from unfired buldings. It was observed the occurrence of peaks in the 150 °C – 250 °C range, that corresponds to a range commonly used in retrospective dosimetry, due to its shorter lifetime when compared with TL geological signal. The analysis of the peaks was done through several well known methods, namely the peak shape (PS), curve fitting (CF) and heating rate (HR) methods. To confirm the structure of the sample, additional X-ray diffraction was made.

MOSFET electronic devices have been used for dosimetry in radiology and radiotherapy. Several communications show that due to the radiation exposure defects appear on the semiconductor crystal lattice. Actually, the structure of a MOSFET consists of three materials: a semiconductor, a metal and an insulator between them. The MOSFET is a quadripolar device with a common terminal: gate-source is the input; drain-source is the output. The gate controls the electrical current passing through semiconductor medium by the field effect because the silicon oxide acts as insulating material. The proposal of this work is to show some radiation effects on the insulator of a MOSFET device. A 6430 Keithley sub-femtoamp SourceMeter was used to verify how the insulating material layer in the structure of the device varies with the radiation exposure. We have used the IEC 61267 standard radiation X-ray beams generated from a Pantak industrial unit in the radiation energy range of computed tomography. This range was chosen because we are using the MOSFET device as radiation detector for dosimetry in computed tomography. The results showed that the behaviour of the electrical current of the device is different in the insulator and semiconductor structures.

While most complexes in fluorite-type lattices (CaF₂, SrF₂, CdF₂) containing Mn²⁺ impurities remain cubic at all temperatures, electron paramagnetic resonance (EPR) measurements have shown that the one in BaF₂ is tetrahedral below 50K. This surprising behaviour is intrinsic to the centre and not associated to any close defect or pure lattice phase-transition. Through the use of density functional (DFT) calculations we show that the distortion is linked to the unexpected low force constant along the tetrahedral distortion mode with a_2u symmetry in these complexes and the large metal-ligand distance existing in BaF₂:Mn²⁺. Ultimately, these facts reflect that, for substitutional impurities in fluorite-type crystals, the ligand-ligand interaction is dominant over the metal-ligand one.

The classification of optical glass and empirical relations between the refractive index and its dispersion are discussed in terms of moments of the glass's IR and UV absorption spectra. The observed linear dependence of index on dispersion within glass families is shown to arise primarily from the approximately linear superposition of the electronic absorptions of glass former and glass modifiers. The binary classification into crown and flint glasses is also based primarily on electronic spectra: Crown glasses are "wide-gap" materials with excitation energies greater than ~12.4 eV, while flint glasses are their "narrow-gap" counterpart.

Ab-initio calculations based on density functional theory have been employed to study electronic properties of Cr doped Bi₄Ge₃O₁₂ (BGO), as well as its optical absorption spectra in ultraviolet region. Two different situations have been analyzed: when the Cr is situated at the Ge position (Cr⁴⁺), and when it resides at the Bi site (Cr³⁺). For each case the band structure and absorption spectra were calculated, and the Cr contributions identified and interpreted. Comparison with the experimental data indicates that the Cr enters both the Ge and Bi sites during the doping.

Ab-initio calculations based on density functional theory have been employed to study the electronic and some optical properties of Y and Nb doped α-Al₂O₃ with corundum structure. The Nd presence elevates the static dielectric constant of the pure alumina, but changes significantly its band offset. Doping with Y preserves the band gap value and increases slightly the dielectric constant of the pure alumina, thus showing a potential to be used in semiconductor industry.

Here we report a computational study of the structure, thermodynamic and spectroscopic properties of 1:1 and 2:1 inclusion complexes of luminescent porphyrins in β-cyclodextrin. Semiempirical PM6 (Parametric Method 6) calculation allowed the optimization of the structure of the complexes, showing that the inclusion in the CD cavity changes significantly the porphyrin ring planarity for the 2:1 complexes. Thermodynamic calculations evidenced that the inclusion complex formation is slightly endothermic and that it is a non-spontaneous process in the absence of water molecules. Finally the calculated spectra were found to be in very good agreement to previously reported experimental ones.

The phase transition of a random mixed-bond Ising ferromagnet on a cubic lattice model is studied both numerically and analytically. In this work, we use the Metropolis and Wolff algorithm with histogram technique and finite size scaling theory to simulate the dynamics of the system. We obtained the thermodynamic quantities such as magnetization, susceptibility, and specific heat. Our results were compared with those obtained using a new technique in effective field theory that employs similar probability distribution within the framework of two-site clusters.

The Monte Carlo technique is here used for study the behavior of metamagnet Ising model in presence of random field. The phase diagram is obtained by employing Glauber's algorithm in a cubic lattice of linear size L with values ranging from 16 to 42 and with periodic boundary conditions.

A computational study of KYF₄, KY₃F₁₀ and K₂YF₅ is presented. Energy minimisation techniques have been used to obtain structural models of the materials and intrinsic defect calculations have been performed. Rare earth doping has been considered at all cation sites and solution energies are presented which show the preference of isovalent doping at the Y³⁺ site.

Topological defects generally they occur in a system when phase transitions take place. We have examples of arrangements with these defects both in Gravitation and Condensed Matter. Depending on how they are generated, this kind of defects make the space present curvature or torsion. There is a wide literature about this matter, much from a gauge field point of view [1, 2, 3], and probing different aspects [6] as the existence of Landau levels [4, 5] or quantum phases [7], for example. However, there is not an unique fundamental theory for describing defects in solids. In our work we follow the Geometric Thery of Defects (TGD) which has the work by Katanaev [8] as a good way of describing continuum media with topological defects. This last theoretical framework is our compass. Besides, we are interested in mesoscopic systems, an important subject right before the role played by nanodevices. In our work we study quantum rings in a space with a screw dislocation. This kind of space presents torsion. The confinement is modelled by a potential that describes different kinds of mesoscopic systems (quantum dots, antidots and quantum wires). We found some results showing the changes in the behaviour of properties as energy eigenvalues and magnetization.

We present the results of computer simulation studies for all 10 different crystalline phases of the strontium aluminate family. After deriving a reliable potential model that reproduces all structures, the energetic process involving in creation of intrinsic defects were calculated, namely the Schottky, pseudo-Schottky, anti-Schottky, and Frenkel defects. The results indicated that the entire family of strontium aluminates can be divided in three groups according to the type of the predominant intrinsic defect formed, SrO pseudo-Schottky defect, oxygen Frenkel defect or Strontium Frenkel defect.

Single crystal fibers of pure and Nd³⁺-doped NaLa(WO₄)₂ were grown by the micro-pulling down method (μPD) under air atmosphere. The starting materials were synthesized through solid state reaction. Inductive and resistive configurations of μPD systems were tested. The control of the growth process was better achieved through the resistive mode than in the inductive one. Optical and structural properties are compatible with the data already reported in the literature for bulk crystals of this host.

The growth of single crystal fibers of LiYF₄ (YLF) doped with Er³⁺ was studied through the resistive micro-pulling-down (μ-PD) technique. The growth chamber was modified to achieve vacuum of approximately 10⁻⁷torr. Single crystal fibers of YLF: Er (1, 10 and 20 mol %), with 0.7 mm of diameter and up to 120mm of length were grown. The use of a static atmosphere was found to be inappropriate for elimination of spurious contamination from growth environment for this experimental setup.

This contribution reports a study of the preparation of pure and doped delafossite-type material CuInO₂ using pulsed laser deposition. A series of films have been prepared at different oxygen partial pressures. X-ray absorption spectroscopy (XAS) has been used to characterise the microstructure of the films. The results show that the structure of the films is extremely sensitive to the preparation conditions.

Mixed crystals based on scheelites type LiLnF₄ (Ln = lanthanides, Y) are an alternative in the development materials with better structural features to be doped with light rare earth ions. In this work a LiGd_0.232Lu_0.75Nd_0.018F₄ crystal was successfully grown using the Czochralski method in a commercial system with automated diameter control, under a mixed atmosphere of argon and CF₄. It was demonstrated that G25L75LF:Nd is an ideal solid solution that can be obtained with good optical quality from its stoichiometric composition. The spectroscopic studies showed that Nd presents larger bandwidth at 792 and 797 nm, which can be suitable to obtain a laser medium for mode-locking purposes.

Energy transfer processes that generate thulium blue and ultraviolet emissions by upconversion were studied in KY₃F₁₀:Tm (KY3F:Tm), using Nd³⁺ and Yb³⁺ as sensitizers of Tm³⁺. The upconversion mechanisms were determined by exciting into the Nd and Tm absorption bands with a diode laser at 797nm. It was observed that the intensity of the Tm³⁺ blue and ultraviolet emissions in 484, 453, 366 and 350 nm were very dependent of the Yb³⁺ concentration in the samples, confirming that the main energy transfer processes involve Nd³⁺ and Yb³⁺ ions. KY₃F₁₀:Nd (1.3 mol%):Tm (0.5 mol%) crystals codoped with 5, 10, 20 and 30 mol% Yb were prepared by slow cooling from the melt, to establish the optimal Yb concentration that maximizes the Nd³⁺→Yb³⁺→Tm³⁺ energy transfer.

Multi-component soda lime silica glass (SLSG) specimens, with composition from the miscibility gap in the SiO₂-Na₂O system, were investigated after the substitution of copper for sodium and after thermal treatment of the exchanged samples in gaseous hydrogen. The behaviour of the obtained composite materials was studied by infrared reflection spectroscopy (IRRS). Some optical absorption micro-spectrophotometry (OAMS) measurements and X-ray-diffraction (XRD) analyses complemented these investigations. It has been stated that after exchange in the CuCl molten bath, the dopant was present in the glassy matrix in the form of cuprous and cupric ions. The cuprous ions participate in the formation of semiconducting Cu₂O nanoparticles. Hydrogenation of the exchanged specimens leads to the formation of metallic copper atoms which due to the van der Waals interactions precipitate in the form of colloidal copper nanoparticles. Changes of the matrix morphology are mainly related with the presence of cupric ions which behave as glass forming cations and such as these participate in the formation of mixed copper-sodium silicates. The effectiveness of these processes is substantially dependent on the exchange and hydrogenation parameters.

Hydroxyapatite (HAP) have been used as starting material for biomedical applications. The pure and Cr³⁺ -doped hydroxyapatite were prepared by chemical precipitation reactions at 100, 500 e 800 °C in order to investigate the thermal stability of these materials. The characterization of the thermal behavior of this phosphate, especially on the structural changes with heating, is very important for production of sunscreens The powders were characterized using chemical analysis: X-ray diffraction (XRD) and thermal analysis. The present study was successful in the preparation of pure hydroxyapatite and chromium substituted hydroxyapatites with good thermal stability and nanoparticles formation.

The kinetic parameters for the crystallization of CH₃COOLi/CH₃COONa glasses varying the Li:Na mole fraction LN21(2:1), LN31(3:1), LN41(4:1) and LN32(3:2) have been evaluated by isothermal and non-isothermal DSC measurements. Crystallization of LN21 samples containing variable amounts of poly(ethylene-terephthalate) (PET) has also been studied. Values of the Avrami exponent n varying between 2.05 and 2.33 were obtained from both isothermal and non-isothermal methods for all LN glasses, indicating a diffusion-controlled crystal growth with a decreasing nucleation rate. The more pronounced effect of PET on glass crystallization has been observed for low polymer amounts, being interpreted as due to polymer miscibility with the glass, which is absent for high PET amounts. The value of n = 4.75 for LN21+PET (3%) suggests a change in the crystallization mechanism from diffusion-controlled to interface-controlled crystal growth. The apparent activation energy (E) decreased with increasing PET amount, evidencing an improvement in glass stability against crystallization.

The hyperfine field at metal lattice sites in a nanostructured HfO₂ thin film was studied by the Perturbed Angular Correlation (PAC) technique using ¹⁸¹Ta as probe nuclei. The thin oxide film was deposited by pulsed laser ablation on a silicon substrate kept at 673 K. The resulting film thickness was about 25 nm. The ¹⁸¹Ta isotopes are formed in Hf sites of the sample as disintegration product of radioactive ¹⁸¹Hf, which were produced by neutron activation of the very thin film by the reaction ¹⁸⁰Hf(n,γ)¹⁸¹Hf.. PAC measurements of the electric field gradient at the ¹⁸¹Ta probe sites .were performed with the thin film in the temperature range 295 – 1273 K in vacuum. Results showed that the film has a single crystalline structure and two different quadrupole frequencies could be observed corresponding to ¹⁸¹Ta at monoclinic structure and with oxygen vacancy in its neighborhood.

Mg²⁺ and Nd³⁺ doped aluminium oxide samples were produced by polymer calcination method. Mg²⁺ doped samples did not exhibited significant fluorescence emission, using IR (LED, emission centered at 862nm) or green (Xe-lamp plus optical filter, emission centered at 520 nm) sources. Nonetheless, high thermostimulated luminescence was detected, with high emission peak at 190°C. A nanoscopic layer (about 50 nm width) of magnesium spinel was observed by Transmission Electronic Microscopy (TEM) for 2.61mol% doped sample; this layer can be the responsible for TL enhancement. Nd³⁺ doped sample exhibited low phosphorescence emission in the UV (Schott U-340) using IR source. TL peaks were detected at 185 and 265°C; the intermediary peak showed the highest emission. Occurrence of NdAl and NdAl₂ structures were detected in 5 mol% doped sample and NdAl₂ and NdAl₄ structures in 10 mol% doped sample.

Wide band-gap semiconductors, particularly III-nitrides, became one of the most studied materials during the last decades. These compounds are the base of a new generation of optoelectronic devices operating in the UV-Blue region of the electromagnetic spectrum. Incorporation of rare-earth (RE) ions into nitrides creates new routes to build all-nitride electroluminescent devices, using the sharp intra-4fⁿ transitions of these elements. The introduction of the RE ions in the nitride lattice during the growth or by ion implantation creates defects which influence the optical behaviour of the doped region. In this work we report the results on Yb implanted GaN. A combination of techniques (Rutherford backscattering/Channeling and Photoluminescence) was used to assess the mechanisms responsible for the optical and structural behaviour of the doped materials. Lattice site location experiments showed that Yb is incorporated into positions slightly displaced from the Ga-site. Clearly the optical activity of the RE could be enhanced by orders of magnitude reducing the number of non-radiative recombination paths related with defects.

Nanocrystals of Y and Zr doped SnO₂ have been prepared by sol-gel route and annealed at 200, 400, 600, 800 and 1000 ºC. The X-ray diffraction (XRD) results showed the average size of the particles in the freshly prepared samples to be ~ 3 nm. The Extended Absorption Fine Structure (EXAFS) technique was used to study the dopant environments in nanocrystalline tin oxide. In all Y-doped samples, except the one annealed at 1000 ºC, there is clear evidence that Y has not entered the SnO₂ lattice. This is clearly supported by the Raman scattering results. In all Zr-doped samples, there is a simple substitution for Sn by Zr.

Holographic recording in stilbene azobenzene derivatives by He-Ne 633 nm laser light has been experimentally studied. It was found that surface relief gratings (SRG) can be recorded by red light. Usually shorter wavelengths are used to induce the trans-cis photo-isomerization in organic materials. SRG with 2 μm period and an amplitude of 130 nm have been recorded with 0.88 W/cm² light in about 20 minutes in amorphous films of 3-(4-(bis(2-(trityloxy)ethyl)amino)phenyl)-2-(4-(2-bromo-4-nitrophenyl)diazenyl)phenyl)acrylonitrile spin-coated on glass substrates. Self-diffraction efficiency up to 17.4% and specific recording energy down to 114 J/(cm²%) were measured. The recorded SRG were stable as proved by subsequent AFM measurements. The photo-induced changes in absorption spectra did not reveal noticeable signs of trans-cis transformations. Rather, spectrally uniform bleaching of the films took place. We conclude that a photothermally stimulated photo-destruction of chromophores is responsible for the SRG recording. The recording of stable SRG in the stilbene azobenzene derivatives we studied is accompanied by the recording of relaxing volume-phase gratings due to the photo-orientation of chromophores by the linearly polarized recording light. It should also be noted that holographic recording efficiency in stilbene azobenzene derivatives exhibit an unusual non-monotonic sample storage-time dependence presumably caused by the peculiarities of structural relaxation of the films.

We report a study of the conductivity of LiBr and copper salt doped succinonitrile along with X-ray absorption measurements for the bromide and copper ions. The work shows that the ions are in well-ordered sites for most of the plastic phase and relatively high conductivity is due to a small fraction of the ions which are mobile.

Thermoluminescent dosimetric topaz properties have been investigated and the results have shown that this mineral presents characteristics of a good dosimeter mainly in doses evaluation in radiotherapy with photons beams in radiotherapy. Typical applications of thermoluminescent dosimeters in radiotherapy are: in vivo dosimetry on patients (either as a routine quality assurance procedure or for dose monitoring in special cases); verification of treatment techniques; dosimetry audits; and comparisons among hospitals. The mean aim of this work was to evaluate the efficiency of topaz-Teflon pellets as thermoluminescent dosimeters in high-energy electron beams used to radiotherapy. Topaz-Teflon pellets were used as TLD.

The main purpose of this work is the developing of sintered composites in order to allow their use as thermoluminescent dosimeters using a simple route to preparation, employing high temperature. The composites were prepared with CaSO₄.2H₂O doped with EuO₃. Initially CaSO₄.2H₂O was dehydrated in oven at 100°C for 1h. After addition of dopants, glass and homogenization, PVA was incorporated into the compounds to make their compaction easier. The pellets with 6 mm of diameter and 1 mm thick were sintered at 750°C for 6 h. The TL emission curves showed two peaks when the samples were irradiated with beta source (⁹⁰Sr+⁹⁰Y) and X-ray. During calibration, TL responses were found to be proportional to the absorbed dose. The results showed that this material can potentially to be used in dosimetry.

An integrated methodology for the detection and removal of cracks on digitized image is presented in this paper. Crack-like pattern detection have been a matter of high concern among researchers mostly for its useful contribution to a variety of applications. The results presented here regard the craquelure of old paintings, however, the same methodology can be used for a much wider set of application. Many images contain similar patterns: crack in protective coating for polymers and other surfaces; fatigue crack in MEMS/NEMS; crack in epoxies used for underfill and encapsulation microelectronics components; etc. In this paper the cracks are detected by thresholding the output of the morphological top-hat transform. Afterwards, the thin dark brush strokes which have been misidentified as cracks are removed using automatic procedure. Finally, crack filling using texture synthesis algorithms. The methodology has been shown to perform very well on digitized images suffering from cracks.

Documents have taken up a very important place in our society. Frauds committed in connection with documents are not at all uncommon, and, in fact, represent a very large domain of the forensic science called "questioned documents". In the field of forensic examination of questioned documents, the legitimacy of an ink entry is often an essential question. A common type of forgery consists in materially altering an existing writing or adding a new writing. These changes can be characterized by means of optical spectroscopy. The aim of this work is to perform the UV-vis-NIR reflectance spectrophotometry to analyze a range of blue and black commercial ballpoint pens, in order to investigate the discriminating abilities of the different inks found on the same document.

Most of film dosimetry is based on optical signal measurements since the spectrophotometric technique is cheap and widespread. Radiation induced chemical reactions take place in the material creating and/or enhancing absorption bands in the visible and/or ultraviolet regions of the spectrum. The response of most films used in routine dosimetry is usually influenced by the environmental conditions (temperature, humidity, ligth), dose rate and post irradiation storage. Several film dosimeters are commercially available for the absorbed dose measurements, in this work the effects of dose rate changes in optical density (OD) of film dosimeters (polymethylmetacrylate – PMMA and polycarbonate – PC) were investigated and compared. Polycarbonates has been investigated as a new dosimetric material for industrial radiation processing aiming low cost, easy handle, fast and accurate response. PMMA dosimeters has been used routinely in dosimetry. The dose rate (kGy h⁻¹) may influence the dosimeter response and appropriate corrections are necessary. The dosimeters were irradiated with ⁶⁰Co gamma-radiation at dose rate in the range 0.26 – 2.6 kGy h⁻¹ and with electrons from accelerator with maximum energy of 1.5 MeV and dose rate between 4.19 and 33.59 kGy s⁻¹ to absorbed doses of 5 and 15 kGy, respectively. The irradiated dosimeters were measured using Shimadzu UV-2101PC spectrophotometer. It can be observed that the films shows moderate dose-rate dependence (about 10%) in the analised range.

The study of radiation defects created in biomaterials, such as bone and teeth, can be used in dating with importance to palaeontology and archaeology. Two Stegomastodon teeth (AL1 and AL2) from north-eastern Brazilian megafauna were studied by electron spin resonance (ESR) spectroscopy. The samples were collected in Fazenda Ovo da Ema, (913349 / 3714965) UTM, Alagoas state, Brazil. The dating of these samples can contribute to the better knowledge of megafauna presence in this region as well as to the events associated to the extinction of these species.

To discover well the properties of nanothin crystalline layers and nanometer-sized crystals, we investigated the relatively thick multilayer structures composed of high quantity of nanothin layers with nanocrystals. Alternate nanolayers of 150–10 nm thicknesses with LiF, CaF₂ and CdS nanocrystals have been deposited onto irradiation-resistive substrates by thermal evaporation of pure crystals. Some multilayers were γ-irradiated in air at room temperature with dose of 83 kGy. X-ray diffraction and microscopy studies reveal that the multilayers consist of nanocrystals with cubic phase and defined size. Thin-film structures were oriented along the (111) plane. Absorption spectra of non-irradiated LiF nanocrystals of 100 nm size suggest evidence of metal colloids presence. We find that photoluminescence spectra of γ-irradiated nanostructures with metal colloids and various LiF contents show the enhancement of F₃⁺-colour centres excitation in the region of metal colloids absorption and the increase is observed of the emission intensities ratio of F₃⁺ and F₂ centers with respect to initial crystals γ-coloured in identical conditions. Emission intensities of both centers under excitation at 458 nm correlate with LiF content. These effects, which are related to high-quality nanostructures, but at the same time depend strongly on the defect content, especially as far as their 1–2 ps nonlinearities are concerned, could depend on nanocrystal purity and metal excess collection in their boundaries regions. Our results provide an original contribution to the understanding of the influence of the nanolayer-by-nanolayer deposition, γ-irradiation on these specific structures, and of the metal aggregates on the properties of nanocrystals and nanolayers.

The Fricke xylenol gel (FXG) dosimeter has been studied for application in radiotherapy because it is capable of to measure the spatial distribution of radiation doses. The dosimetry is based on the oxidation of ferrous (Fe²⁺) to ferric (Fe³⁺) ions radiation induced, related to the radiation dose. The gel material usually employed is the 300 Bloom gelatin, which is imported and very expensive in Brazil. Aiming to analyze the viability of to use a locally produced and low cost gel material, in this work the spectrophotometric responses of FXG solutions prepared using 270 Bloom gelatin commercially available and 300 Bloom gelatin imported were compared. The absorption spectra of solutions prepared with 5% by weight 270 and 300 Bloom gelatins non-irradiated and irradiated with ⁶⁰Co gamma radiation in the dose range between 0.5 and 100 Gy were analysed, the dose-response curves were evaluated and the useful dose range was established. The obtained results indicate that the FXG solution prepared with 270 Bloom gelatin presents good performance, similar to that presented by the FXG solution prepared with 300 Bloom gelatin and its use can be recommended owing to the low cost and the availability in local market.