Walter Elias Feria Ayta - Academia.edu (original) (raw)

Papers by Walter Elias Feria Ayta

Research paper thumbnail of Thermally stimulated luminescence and conductivity—A critical review of the theoretical treatments and their applicability to experimental results

Radiation Physics and Chemistry, Jun 1, 1998

Thermally stimulated luminescence and conductivity measurements have been performed in natural an... more Thermally stimulated luminescence and conductivity measurements have been performed in natural and synthetic semiconducting diamonds, in the temperature range 12-350 K, after excitation, near liquid-helium or liquid-nitrogen temperatures, with uv light, x-ray, 150-keV, and 0;5-MeV electrons. The glow curves observed in synthetic diamonds are similar to the glow curves obtained previously in natural diamonds. Two of the peaks which are reported have only been previously observed in types-I and-IIa diamonds. Conductivity measurements exhibit stages at 160, 230, and 340 K which correlate with thermoluminescence peaks. An additional stage at 50 K is observed after 0.5-MeV electron irradiation. The concentrations of.the traps in these different stages have been deduced. The stage at 50 K is shown to be associated with a donor level situated at 0.02 eV below the conduction band.

Research paper thumbnail of Thermally stimulated luminescence and conductivity – theoretical models and their applicability to experimental results

Radiation Effects and Defects in Solids, Oct 1, 1998

Thermally stimulated luminescence and conductivity measurements have been performed in natural an... more Thermally stimulated luminescence and conductivity measurements have been performed in natural and synthetic semiconducting diamonds, in the temperature range 12-350 K, after excitation, near liquid-helium or liquid-nitrogen temperatures, with uv light, x-ray, 150-keV, and 0;5-MeV electrons. The glow curves observed in synthetic diamonds are similar to the glow curves obtained previously in natural diamonds. Two of the peaks which are reported have only been previously observed in types-I and-IIa diamonds. Conductivity measurements exhibit stages at 160, 230, and 340 K which correlate with thermoluminescence peaks. An additional stage at 50 K is observed after 0.5-MeV electron irradiation. The concentrations of.the traps in these different stages have been deduced. The stage at 50 K is shown to be associated with a donor level situated at 0.02 eV below the conduction band.

Research paper thumbnail of General-order kinetics of thermoluminescence and its physical meaning

Journal of Physics D, Apr 21, 1997

Thermoluminescence glow peaks are calculated numerically for a one-trap - one-recombination-centr... more Thermoluminescence glow peaks are calculated numerically for a one-trap - one-recombination-centre model using a generalized approach. Except in extreme cases the peaks are seen to change in position and shape with a change in dose. These glow peaks are fitted to the general-order kinetics model and the values of the kinetic parameters, namely the activation energy, pre-exponential factor and order

Research paper thumbnail of Optical and Electron Paramagnetic Resonance Spectroscopies of Mn-Doped PbS Nanocrystals

IEEE Transactions on Magnetics, Jun 1, 2007

Mn-doped PbS nanocrystals (NCs) (Pb 1 x Mn S) embedded in glass matrix have been successfully syn... more Mn-doped PbS nanocrystals (NCs) (Pb 1 x Mn S) embedded in glass matrix have been successfully synthesized by means of fusion method. The geometrical morphology and size dispersion of Pb 1 x Mn x S NCs were studied by atomic force microscopy (AFM). Their magnetic and the optical properties have been investigated using electron paramagnetic resonance (EPR) and optical absorption (OA) measurements. We found that the isolated Mn 2+-ions are located on the PbS NC-shell whereas coupled Mn 2+-ions are located on the Pb 1 x Mn x S NC-core.

Research paper thumbnail of As dunas costeiras inativas do Rio Grande do Norte datadas por termoluminescência e implicações paleoambientais

Research paper thumbnail of Effect of Fe2O3 concentration on the structure of the SiO2–Na2O–Al2O3–B2O3 glass system

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2011

The structural properties of the glass matrix 40SiO(2)·30Na(2)O·1Al(2)O(3)·(29-x)B(2)O(3)·xFe(2)O... more The structural properties of the glass matrix 40SiO(2)·30Na(2)O·1Al(2)O(3)·(29-x)B(2)O(3)·xFe(2)O(3) (mol%), 0.0≤x≤29.0 were studied by X-ray diffraction (XRD), differential thermal analysis (DTA) and Raman and infrared spectroscopy (FT-IR). XRD demonstrated Fe(3)O(4) crystal formation for Fe(2)O(3) concentrations of 29.0 mol%. DTA showed that glass transition and crystallization temperatures changed as a function of Fe(2)O(3) concentration and that these alterations were related to structural change in the glass system. Interesting aspects of Raman and FT-IR spectra were found, and this gives information about of the structure changes in Si-O-Si units of these glasses as a function of Fe(2)O(3) concentration.

Research paper thumbnail of TL, ESR and reflectance in natural diopside crystal

physica status solidi (c), 2007

In this paper, results on thermoluminescence (TL) as well as electron spin resonance (ESR) and re... more In this paper, results on thermoluminescence (TL) as well as electron spin resonance (ESR) and reflectance of Brazilian diopside samples are presented. The behaviour of the TL centres, ESR signal and reflectance bands under irradiation and heat treatments are examined.

Research paper thumbnail of Magnetic and optical investigation of 40SiO2·30Na2O·1Al2O3·(29 − x)B2O3·xFe2O3 glass matrix

Solid State Sciences, 2012

Research paper thumbnail of General order kinetics and its validity in thermoluminescence

Research paper thumbnail of First evidence of crystalline KHS04:Mn grown by an aqueous solution method and the investigation of the effect of ionizing radiation exposure

Journal of Crystal Growth, 2010

Research paper thumbnail of The quasi-equilibrium approximation and its validity for the thermoluminescence of inorganic phosphors

Journal of Physics D: Applied Physics, 1999

ABSTRACT The validity of the quasi-equilibrium (QE) assumption in the analytical models of thermo... more ABSTRACT The validity of the quasi-equilibrium (QE) assumption in the analytical models of thermoluminescence (TL) which assume delocalization of the untrapped charge carriers has often been questioned. In this paper, this problem is further considered using three different physical models of TL emission. The numerically computed glow curves without the QE approximation are compared with those calculated analytically to verify whether the QE condition is satisfied. QE is assessed also by using a mathematical relation between the excitation and relaxation rates. The results lead to the following conclusions. (i) Under a wide variety of parametric combinations QE is attained even when retrapping predomines over recombination. (ii) Glow peaks with first-order character are obtained even when the retrapping rate far exceeds the recombination rate in multiple-trap systems. This is contrary to the premise on which the Randall-Wilkins model is based. These two conclusions contradict also the assertions of Lewandowski and McKeever that QE and fast retrapping are not self-consistent conditions and that the apparent dominance of first-order TL kinetics in nature is due solely to the predominance of recombination over retrapping. (iii) QE depends critically on the product of the trap concentration and the cross section. A new criterion for the validity of the QE assumption is derived, according to which should be greater than , where and are the concentration and the cross section of the traps at the active and deeper levels in a system exhibiting multiple glow peaks. (iv) Evidence from studies of point defects in insulating and semiconducting materials shows that the N and values of the defect centres concerned are high enough to satisfy the QE condition. It is thus inferred that the use of the analytical expressions based on the QE approximation for analysing the glow curves of the common TL phosphors is legitimate.

Research paper thumbnail of Modelo de Armadilhas e Centros de Recombinação Interativos de Termoluminescência Face a Condições Teóricas e Dados Experimentais

ABSTRACT Neste trabalho faz-se uma análise teórica das curvas de emissão termoluminescente (TL) e... more ABSTRACT Neste trabalho faz-se uma análise teórica das curvas de emissão termoluminescente (TL) e das intensidades TL em função da dose da radiação, utilizando o chamado modelo de Sistema de Multi-armadilhas Interativas (SMAI). Esse modelo considera a participação de várias armadilhas (de elétrons para visualizar, mas, que pode ser, de buracos), entre as quais aquelas termicamente ativas (ATA), que dão origem ao pico TL com máximo em temperatura 'T IND. 'mü' as armadilhas rasas (ARA), cujos picos TL ocorrem em T<'T IND. 'mü' as armadilhas profundas termicamente desconectadas (APTD), cujas energias de ativação são maiores do que a das ATA, por isso, termicamente estáveis, daí o nome de desconectadas e, por fim, centros de recombinações (CR) de vários tipos, isto é, de diferentes profundidades. Sem perda de generalidade, nos cálculos numéricos foram restritos a uma ATA, a um tipo de APTD e a um de CR. As armadilhas ARA não afetam em nada a emissão TL em questão enão foram incluídas na análise. A discussão do problema da emissão TL envolve, é claro, vários parâmetros; são eles: a energia de ativação E, o fator de frequência s e pré-exponencial s', a ordem de cinética b, as concentrações das armadilhas ocupadas ou não e dos centros de recombinação, secções de choque de captura das cargas pelas armadilhas e pelos centros de recombinação e velocidade v de cargas livres durante suas transições. A atenção é concentrada no estágio. (Continuação) outros autores, as condições de quase-equilibrio (QE), que permitem encontrar expressões analíticas da intensidade da luz TL emitida. Sem QE, é necessário resolver numericamente o sistema de equações diferenciais. Na realidade, o que aqui foi feito consistiu em se resolver numericamente essas equações diferenciais, usando o método de Runge-Kutta e comparar com as soluções analíticas obtidas com o uso das condições QE. Em particular, dessas comparações, foram analisadas quando e sob que condições, a aproximação QE é válida. A supralinearidade observada experimentalmente é aqui explicada satisfatoriamente com a hipótese de armadilhas profundas termicamente desconectadas, porém, capazes de capturar as cargas liberadas das armadilhas pelo aquecimento, durante a leitura TL. Sabe-se que a supralinearidade foi no início, considerado acontecer durante a irradiação. Há, porém, dados experimentais que mostram que a supralinearidade não pode acontecer na fase de irradiação do material, baseado na observação de que, o mesmo centro responsável pela termoluminescência e pela absorção ótica, cresce linearmente com a dose da radiação, fato comprovado pelo crescimento linear da banda de absorção resultante desses centros. Tese (Doutorado).

Research paper thumbnail of Modelo de Armadilhas e Centros de Recombinação Interativos de Termoluminescência Face a Condições Teóricas e Dados Experimentais

ABSTRACT Neste trabalho faz-se uma análise teórica das curvas de emissão termoluminescente (TL) e... more ABSTRACT Neste trabalho faz-se uma análise teórica das curvas de emissão termoluminescente (TL) e das intensidades TL em função da dose da radiação, utilizando o chamado modelo de Sistema de Multi-armadilhas Interativas (SMAI). Esse modelo considera a participação de várias armadilhas (de elétrons para visualizar, mas, que pode ser, de buracos), entre as quais aquelas termicamente ativas (ATA), que dão origem ao pico TL com máximo em temperatura 'T IND. 'mü' as armadilhas rasas (ARA), cujos picos TL ocorrem em T<'T IND. 'mü' as armadilhas profundas termicamente desconectadas (APTD), cujas energias de ativação são maiores do que a das ATA, por isso, termicamente estáveis, daí o nome de desconectadas e, por fim, centros de recombinações (CR) de vários tipos, isto é, de diferentes profundidades. Sem perda de generalidade, nos cálculos numéricos foram restritos a uma ATA, a um tipo de APTD e a um de CR. As armadilhas ARA não afetam em nada a emissão TL em questão enão foram incluídas na análise. A discussão do problema da emissão TL envolve, é claro, vários parâmetros; são eles: a energia de ativação E, o fator de frequência s e pré-exponencial s', a ordem de cinética b, as concentrações das armadilhas ocupadas ou não e dos centros de recombinação, secções de choque de captura das cargas pelas armadilhas e pelos centros de recombinação e velocidade v de cargas livres durante suas transições. A atenção é concentrada no estágio. (Continuação) outros autores, as condições de quase-equilibrio (QE), que permitem encontrar expressões analíticas da intensidade da luz TL emitida. Sem QE, é necessário resolver numericamente o sistema de equações diferenciais. Na realidade, o que aqui foi feito consistiu em se resolver numericamente essas equações diferenciais, usando o método de Runge-Kutta e comparar com as soluções analíticas obtidas com o uso das condições QE. Em particular, dessas comparações, foram analisadas quando e sob que condições, a aproximação QE é válida. A supralinearidade observada experimentalmente é aqui explicada satisfatoriamente com a hipótese de armadilhas profundas termicamente desconectadas, porém, capazes de capturar as cargas liberadas das armadilhas pelo aquecimento, durante a leitura TL. Sabe-se que a supralinearidade foi no início, considerado acontecer durante a irradiação. Há, porém, dados experimentais que mostram que a supralinearidade não pode acontecer na fase de irradiação do material, baseado na observação de que, o mesmo centro responsável pela termoluminescência e pela absorção ótica, cresce linearmente com a dose da radiação, fato comprovado pelo crescimento linear da banda de absorção resultante desses centros. Tese (Doutorado).

Research paper thumbnail of Limitation of peak fitting and peak shape methods for determination of activation energy of thermoluminescence glow peaks

Radiation Measurements, 1999

This paper shows the limitation of general order peak ®tting and peak shape methods for determini... more This paper shows the limitation of general order peak ®tting and peak shape methods for determining the activation energy of the thermoluminescence glow peaks in the cases in which retrapping probability is much higher than the recombination probability and the traps are ®lled up to near saturation level. Right values can be obtained when the trap occupancy is reduced by using small doses or by post-irradiation partial bleaching. This limitation in the application of these methods has not been indicated earlier. In view of the unknown nature of kinetics in the experimental samples, it is recommended that these methods of activation energy determination should be applied only at doses well below the saturation dose. #

Research paper thumbnail of Interactive Trap System Model and the Behavior of Thermoluminescence Glow Peaks

Materials Science Forum, 1997

Research paper thumbnail of Magnetic and optical investigation of 40SiO2·30Na2O·1Al2O3·(29 − x)B2O3·xFe2O3 glass matrix

Samples of 40SiO 2 30Na2O30Na 2 O30Na2O1Al 2 O 3 (29Aˋx)B2O3(29 À x)B 2 O 3 (29Aˋx)B2O3xFe 2 O 3 (mol%), with 0.0

Research paper thumbnail of The electronic and optical properties of sodalite from first principles

Solid State Communications, 2010

This study reports the results of ab initio electronic and optical calculations for pure sodalite... more This study reports the results of ab initio electronic and optical calculations for pure sodalite crystal using the linear augmented plane wave (LAPW) method within density functional theory (DFT). The calculated electronic structure revealed predominantly orbital characters of the valence band and the conduction band, and enabled us to determine the type and the value of the fundamental gap of the compound. The imaginary part of the dielectric tensor, extinction coefficient and refraction index were calculated as functions of the incident radiation wavelength. It is shown that the O 2p states and Na 3s states play the major role in optical transitions as initial and final states, respectively. The absorption spectrum is localized in the ultraviolet range between 40 and 250 nm. Furthermore, we concluded that the material does not absorb radiation in the visible range.

Research paper thumbnail of Quasi-Equilibrium Assumption in Analytical Models of Thermoluminescence and its Validity in Practical Cases

Radiation Protection Dosimetry, 1999

ABSTRACT Thermoluminescence (TL) intensity I(T), Q(T) and P(T) as a function of temperature T dur... more ABSTRACT Thermoluminescence (TL) intensity I(T), Q(T) and P(T) as a function of temperature T during glow curve readout are calculated numerically for three types of physical models, where Q(T) is called the quasi-equilibrium (QE) function and P(T) is the ratio of the retrapping to recombination rates. The models include a one trap-one recombination centre and an interactive or non-interactive deep trap. The results lead to the following conclusion: (1) Under a wide variety of parametric combinations Q(T) ( 1 and P(T) � 1 is a more common condition that Q(T) ( 1 and P(T) � 1. (2) Glow peaks with first order character are obtained even when P(T) � 1 which is contrary to the Randall and Wilkins Theory. These two conclusions are in clear contradiction to the assertions of Lewandowski and McKeever that Q(T) ( 1 and P(T) � 1 are not self-consistent conditions and that the dominance of first order TL kinetics in nature is explained only with P(T) � 1. This paper also discusses the practical side of the QE assumption in relation to the real materials and infers that the QE condition is most likely to prevail in the TL emission of common phosphors.

Research paper thumbnail of On the Quasi-equilibrium Problem in Thermally Stimulated Luminescence and Conductivity

Radiation Protection Dosimetry, 2002

Strong doubts havc been expressed about the validity of the quasi-equilibrium (QE) assumption use... more Strong doubts havc been expressed about the validity of the quasi-equilibrium (QE) assumption used in the derivation of the analytical expressions of thermoluminescence (TL). So far there is no established method available to check if QE actually prevails during the emission of an experimental TL signal. The present study shows that the level of QE changes with a change in the heating rate beta. The change in the level of QE in its turn gets reflected in a change in peak shape when the system turns to a non-QE condition. This property is used as the first ever experimental method to test whether or not the emission of a given glow peak occurs under the QE condition. An essential condition for holding the QE condition is found to be T(R)/taum> or = 10(-3) where T(R) and taum are the glow peak recording duration and the maximum value of the free carrier lifetime, respectively. This relation between T(R) and taum is useful in finding the approximate value of taum. The value of taum being a function of the concentration and cross section of the TL related centres, one may be able to assess these basic parameters from the study of TL glow curves. The theoretical results are discussed in the perspective of LiF (TLD-100).

Research paper thumbnail of Theoretical Models of Thermoluminescence and Their Relevance in Experimental Work

Radiation Protection Dosimetry, 1999

ABSTRACT TL glow peaks are computed for different models by varying the input parameters. The phy... more ABSTRACT TL glow peaks are computed for different models by varying the input parameters. The physical models considered consist of (1) one trap and one recombination centre (RC), (2) multi-trap non-interactive and (3) multi-trap interactive schemes. The characteristics of these glow peaks are discussed in the perspective of the experimental glow curve properties, namely the effect of dose on temperature of glow peak maximum, on shape of the glow curve and supralinearity of response. The results obtained lead to the following conclusions: (1) The glow peak properties of the one trap one RC system, the multi-trap non-interactive system and the so-called general order do not generally tally with those observed in experimental samples. (2) The multi-trap interactive scheme is capable of producing glow peaks whose characteristics match with the experimental properties.

Research paper thumbnail of Thermally stimulated luminescence and conductivity—A critical review of the theoretical treatments and their applicability to experimental results

Radiation Physics and Chemistry, Jun 1, 1998

Thermally stimulated luminescence and conductivity measurements have been performed in natural an... more Thermally stimulated luminescence and conductivity measurements have been performed in natural and synthetic semiconducting diamonds, in the temperature range 12-350 K, after excitation, near liquid-helium or liquid-nitrogen temperatures, with uv light, x-ray, 150-keV, and 0;5-MeV electrons. The glow curves observed in synthetic diamonds are similar to the glow curves obtained previously in natural diamonds. Two of the peaks which are reported have only been previously observed in types-I and-IIa diamonds. Conductivity measurements exhibit stages at 160, 230, and 340 K which correlate with thermoluminescence peaks. An additional stage at 50 K is observed after 0.5-MeV electron irradiation. The concentrations of.the traps in these different stages have been deduced. The stage at 50 K is shown to be associated with a donor level situated at 0.02 eV below the conduction band.

Research paper thumbnail of Thermally stimulated luminescence and conductivity – theoretical models and their applicability to experimental results

Radiation Effects and Defects in Solids, Oct 1, 1998

Thermally stimulated luminescence and conductivity measurements have been performed in natural an... more Thermally stimulated luminescence and conductivity measurements have been performed in natural and synthetic semiconducting diamonds, in the temperature range 12-350 K, after excitation, near liquid-helium or liquid-nitrogen temperatures, with uv light, x-ray, 150-keV, and 0;5-MeV electrons. The glow curves observed in synthetic diamonds are similar to the glow curves obtained previously in natural diamonds. Two of the peaks which are reported have only been previously observed in types-I and-IIa diamonds. Conductivity measurements exhibit stages at 160, 230, and 340 K which correlate with thermoluminescence peaks. An additional stage at 50 K is observed after 0.5-MeV electron irradiation. The concentrations of.the traps in these different stages have been deduced. The stage at 50 K is shown to be associated with a donor level situated at 0.02 eV below the conduction band.

Research paper thumbnail of General-order kinetics of thermoluminescence and its physical meaning

Journal of Physics D, Apr 21, 1997

Thermoluminescence glow peaks are calculated numerically for a one-trap - one-recombination-centr... more Thermoluminescence glow peaks are calculated numerically for a one-trap - one-recombination-centre model using a generalized approach. Except in extreme cases the peaks are seen to change in position and shape with a change in dose. These glow peaks are fitted to the general-order kinetics model and the values of the kinetic parameters, namely the activation energy, pre-exponential factor and order

Research paper thumbnail of Optical and Electron Paramagnetic Resonance Spectroscopies of Mn-Doped PbS Nanocrystals

IEEE Transactions on Magnetics, Jun 1, 2007

Mn-doped PbS nanocrystals (NCs) (Pb 1 x Mn S) embedded in glass matrix have been successfully syn... more Mn-doped PbS nanocrystals (NCs) (Pb 1 x Mn S) embedded in glass matrix have been successfully synthesized by means of fusion method. The geometrical morphology and size dispersion of Pb 1 x Mn x S NCs were studied by atomic force microscopy (AFM). Their magnetic and the optical properties have been investigated using electron paramagnetic resonance (EPR) and optical absorption (OA) measurements. We found that the isolated Mn 2+-ions are located on the PbS NC-shell whereas coupled Mn 2+-ions are located on the Pb 1 x Mn x S NC-core.

Research paper thumbnail of As dunas costeiras inativas do Rio Grande do Norte datadas por termoluminescência e implicações paleoambientais

Research paper thumbnail of Effect of Fe2O3 concentration on the structure of the SiO2–Na2O–Al2O3–B2O3 glass system

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2011

The structural properties of the glass matrix 40SiO(2)·30Na(2)O·1Al(2)O(3)·(29-x)B(2)O(3)·xFe(2)O... more The structural properties of the glass matrix 40SiO(2)·30Na(2)O·1Al(2)O(3)·(29-x)B(2)O(3)·xFe(2)O(3) (mol%), 0.0≤x≤29.0 were studied by X-ray diffraction (XRD), differential thermal analysis (DTA) and Raman and infrared spectroscopy (FT-IR). XRD demonstrated Fe(3)O(4) crystal formation for Fe(2)O(3) concentrations of 29.0 mol%. DTA showed that glass transition and crystallization temperatures changed as a function of Fe(2)O(3) concentration and that these alterations were related to structural change in the glass system. Interesting aspects of Raman and FT-IR spectra were found, and this gives information about of the structure changes in Si-O-Si units of these glasses as a function of Fe(2)O(3) concentration.

Research paper thumbnail of TL, ESR and reflectance in natural diopside crystal

physica status solidi (c), 2007

In this paper, results on thermoluminescence (TL) as well as electron spin resonance (ESR) and re... more In this paper, results on thermoluminescence (TL) as well as electron spin resonance (ESR) and reflectance of Brazilian diopside samples are presented. The behaviour of the TL centres, ESR signal and reflectance bands under irradiation and heat treatments are examined.

Research paper thumbnail of Magnetic and optical investigation of 40SiO2·30Na2O·1Al2O3·(29 − x)B2O3·xFe2O3 glass matrix

Solid State Sciences, 2012

Research paper thumbnail of General order kinetics and its validity in thermoluminescence

Research paper thumbnail of First evidence of crystalline KHS04:Mn grown by an aqueous solution method and the investigation of the effect of ionizing radiation exposure

Journal of Crystal Growth, 2010

Research paper thumbnail of The quasi-equilibrium approximation and its validity for the thermoluminescence of inorganic phosphors

Journal of Physics D: Applied Physics, 1999

ABSTRACT The validity of the quasi-equilibrium (QE) assumption in the analytical models of thermo... more ABSTRACT The validity of the quasi-equilibrium (QE) assumption in the analytical models of thermoluminescence (TL) which assume delocalization of the untrapped charge carriers has often been questioned. In this paper, this problem is further considered using three different physical models of TL emission. The numerically computed glow curves without the QE approximation are compared with those calculated analytically to verify whether the QE condition is satisfied. QE is assessed also by using a mathematical relation between the excitation and relaxation rates. The results lead to the following conclusions. (i) Under a wide variety of parametric combinations QE is attained even when retrapping predomines over recombination. (ii) Glow peaks with first-order character are obtained even when the retrapping rate far exceeds the recombination rate in multiple-trap systems. This is contrary to the premise on which the Randall-Wilkins model is based. These two conclusions contradict also the assertions of Lewandowski and McKeever that QE and fast retrapping are not self-consistent conditions and that the apparent dominance of first-order TL kinetics in nature is due solely to the predominance of recombination over retrapping. (iii) QE depends critically on the product of the trap concentration and the cross section. A new criterion for the validity of the QE assumption is derived, according to which should be greater than , where and are the concentration and the cross section of the traps at the active and deeper levels in a system exhibiting multiple glow peaks. (iv) Evidence from studies of point defects in insulating and semiconducting materials shows that the N and values of the defect centres concerned are high enough to satisfy the QE condition. It is thus inferred that the use of the analytical expressions based on the QE approximation for analysing the glow curves of the common TL phosphors is legitimate.

Research paper thumbnail of Modelo de Armadilhas e Centros de Recombinação Interativos de Termoluminescência Face a Condições Teóricas e Dados Experimentais

ABSTRACT Neste trabalho faz-se uma análise teórica das curvas de emissão termoluminescente (TL) e... more ABSTRACT Neste trabalho faz-se uma análise teórica das curvas de emissão termoluminescente (TL) e das intensidades TL em função da dose da radiação, utilizando o chamado modelo de Sistema de Multi-armadilhas Interativas (SMAI). Esse modelo considera a participação de várias armadilhas (de elétrons para visualizar, mas, que pode ser, de buracos), entre as quais aquelas termicamente ativas (ATA), que dão origem ao pico TL com máximo em temperatura 'T IND. 'mü' as armadilhas rasas (ARA), cujos picos TL ocorrem em T<'T IND. 'mü' as armadilhas profundas termicamente desconectadas (APTD), cujas energias de ativação são maiores do que a das ATA, por isso, termicamente estáveis, daí o nome de desconectadas e, por fim, centros de recombinações (CR) de vários tipos, isto é, de diferentes profundidades. Sem perda de generalidade, nos cálculos numéricos foram restritos a uma ATA, a um tipo de APTD e a um de CR. As armadilhas ARA não afetam em nada a emissão TL em questão enão foram incluídas na análise. A discussão do problema da emissão TL envolve, é claro, vários parâmetros; são eles: a energia de ativação E, o fator de frequência s e pré-exponencial s', a ordem de cinética b, as concentrações das armadilhas ocupadas ou não e dos centros de recombinação, secções de choque de captura das cargas pelas armadilhas e pelos centros de recombinação e velocidade v de cargas livres durante suas transições. A atenção é concentrada no estágio. (Continuação) outros autores, as condições de quase-equilibrio (QE), que permitem encontrar expressões analíticas da intensidade da luz TL emitida. Sem QE, é necessário resolver numericamente o sistema de equações diferenciais. Na realidade, o que aqui foi feito consistiu em se resolver numericamente essas equações diferenciais, usando o método de Runge-Kutta e comparar com as soluções analíticas obtidas com o uso das condições QE. Em particular, dessas comparações, foram analisadas quando e sob que condições, a aproximação QE é válida. A supralinearidade observada experimentalmente é aqui explicada satisfatoriamente com a hipótese de armadilhas profundas termicamente desconectadas, porém, capazes de capturar as cargas liberadas das armadilhas pelo aquecimento, durante a leitura TL. Sabe-se que a supralinearidade foi no início, considerado acontecer durante a irradiação. Há, porém, dados experimentais que mostram que a supralinearidade não pode acontecer na fase de irradiação do material, baseado na observação de que, o mesmo centro responsável pela termoluminescência e pela absorção ótica, cresce linearmente com a dose da radiação, fato comprovado pelo crescimento linear da banda de absorção resultante desses centros. Tese (Doutorado).

Research paper thumbnail of Modelo de Armadilhas e Centros de Recombinação Interativos de Termoluminescência Face a Condições Teóricas e Dados Experimentais

ABSTRACT Neste trabalho faz-se uma análise teórica das curvas de emissão termoluminescente (TL) e... more ABSTRACT Neste trabalho faz-se uma análise teórica das curvas de emissão termoluminescente (TL) e das intensidades TL em função da dose da radiação, utilizando o chamado modelo de Sistema de Multi-armadilhas Interativas (SMAI). Esse modelo considera a participação de várias armadilhas (de elétrons para visualizar, mas, que pode ser, de buracos), entre as quais aquelas termicamente ativas (ATA), que dão origem ao pico TL com máximo em temperatura 'T IND. 'mü' as armadilhas rasas (ARA), cujos picos TL ocorrem em T<'T IND. 'mü' as armadilhas profundas termicamente desconectadas (APTD), cujas energias de ativação são maiores do que a das ATA, por isso, termicamente estáveis, daí o nome de desconectadas e, por fim, centros de recombinações (CR) de vários tipos, isto é, de diferentes profundidades. Sem perda de generalidade, nos cálculos numéricos foram restritos a uma ATA, a um tipo de APTD e a um de CR. As armadilhas ARA não afetam em nada a emissão TL em questão enão foram incluídas na análise. A discussão do problema da emissão TL envolve, é claro, vários parâmetros; são eles: a energia de ativação E, o fator de frequência s e pré-exponencial s', a ordem de cinética b, as concentrações das armadilhas ocupadas ou não e dos centros de recombinação, secções de choque de captura das cargas pelas armadilhas e pelos centros de recombinação e velocidade v de cargas livres durante suas transições. A atenção é concentrada no estágio. (Continuação) outros autores, as condições de quase-equilibrio (QE), que permitem encontrar expressões analíticas da intensidade da luz TL emitida. Sem QE, é necessário resolver numericamente o sistema de equações diferenciais. Na realidade, o que aqui foi feito consistiu em se resolver numericamente essas equações diferenciais, usando o método de Runge-Kutta e comparar com as soluções analíticas obtidas com o uso das condições QE. Em particular, dessas comparações, foram analisadas quando e sob que condições, a aproximação QE é válida. A supralinearidade observada experimentalmente é aqui explicada satisfatoriamente com a hipótese de armadilhas profundas termicamente desconectadas, porém, capazes de capturar as cargas liberadas das armadilhas pelo aquecimento, durante a leitura TL. Sabe-se que a supralinearidade foi no início, considerado acontecer durante a irradiação. Há, porém, dados experimentais que mostram que a supralinearidade não pode acontecer na fase de irradiação do material, baseado na observação de que, o mesmo centro responsável pela termoluminescência e pela absorção ótica, cresce linearmente com a dose da radiação, fato comprovado pelo crescimento linear da banda de absorção resultante desses centros. Tese (Doutorado).

Research paper thumbnail of Limitation of peak fitting and peak shape methods for determination of activation energy of thermoluminescence glow peaks

Radiation Measurements, 1999

This paper shows the limitation of general order peak ®tting and peak shape methods for determini... more This paper shows the limitation of general order peak ®tting and peak shape methods for determining the activation energy of the thermoluminescence glow peaks in the cases in which retrapping probability is much higher than the recombination probability and the traps are ®lled up to near saturation level. Right values can be obtained when the trap occupancy is reduced by using small doses or by post-irradiation partial bleaching. This limitation in the application of these methods has not been indicated earlier. In view of the unknown nature of kinetics in the experimental samples, it is recommended that these methods of activation energy determination should be applied only at doses well below the saturation dose. #

Research paper thumbnail of Interactive Trap System Model and the Behavior of Thermoluminescence Glow Peaks

Materials Science Forum, 1997

Research paper thumbnail of Magnetic and optical investigation of 40SiO2·30Na2O·1Al2O3·(29 − x)B2O3·xFe2O3 glass matrix

Samples of 40SiO 2 30Na2O30Na 2 O30Na2O1Al 2 O 3 (29Aˋx)B2O3(29 À x)B 2 O 3 (29Aˋx)B2O3xFe 2 O 3 (mol%), with 0.0

Research paper thumbnail of The electronic and optical properties of sodalite from first principles

Solid State Communications, 2010

This study reports the results of ab initio electronic and optical calculations for pure sodalite... more This study reports the results of ab initio electronic and optical calculations for pure sodalite crystal using the linear augmented plane wave (LAPW) method within density functional theory (DFT). The calculated electronic structure revealed predominantly orbital characters of the valence band and the conduction band, and enabled us to determine the type and the value of the fundamental gap of the compound. The imaginary part of the dielectric tensor, extinction coefficient and refraction index were calculated as functions of the incident radiation wavelength. It is shown that the O 2p states and Na 3s states play the major role in optical transitions as initial and final states, respectively. The absorption spectrum is localized in the ultraviolet range between 40 and 250 nm. Furthermore, we concluded that the material does not absorb radiation in the visible range.

Research paper thumbnail of Quasi-Equilibrium Assumption in Analytical Models of Thermoluminescence and its Validity in Practical Cases

Radiation Protection Dosimetry, 1999

ABSTRACT Thermoluminescence (TL) intensity I(T), Q(T) and P(T) as a function of temperature T dur... more ABSTRACT Thermoluminescence (TL) intensity I(T), Q(T) and P(T) as a function of temperature T during glow curve readout are calculated numerically for three types of physical models, where Q(T) is called the quasi-equilibrium (QE) function and P(T) is the ratio of the retrapping to recombination rates. The models include a one trap-one recombination centre and an interactive or non-interactive deep trap. The results lead to the following conclusion: (1) Under a wide variety of parametric combinations Q(T) ( 1 and P(T) � 1 is a more common condition that Q(T) ( 1 and P(T) � 1. (2) Glow peaks with first order character are obtained even when P(T) � 1 which is contrary to the Randall and Wilkins Theory. These two conclusions are in clear contradiction to the assertions of Lewandowski and McKeever that Q(T) ( 1 and P(T) � 1 are not self-consistent conditions and that the dominance of first order TL kinetics in nature is explained only with P(T) � 1. This paper also discusses the practical side of the QE assumption in relation to the real materials and infers that the QE condition is most likely to prevail in the TL emission of common phosphors.

Research paper thumbnail of On the Quasi-equilibrium Problem in Thermally Stimulated Luminescence and Conductivity

Radiation Protection Dosimetry, 2002

Strong doubts havc been expressed about the validity of the quasi-equilibrium (QE) assumption use... more Strong doubts havc been expressed about the validity of the quasi-equilibrium (QE) assumption used in the derivation of the analytical expressions of thermoluminescence (TL). So far there is no established method available to check if QE actually prevails during the emission of an experimental TL signal. The present study shows that the level of QE changes with a change in the heating rate beta. The change in the level of QE in its turn gets reflected in a change in peak shape when the system turns to a non-QE condition. This property is used as the first ever experimental method to test whether or not the emission of a given glow peak occurs under the QE condition. An essential condition for holding the QE condition is found to be T(R)/taum> or = 10(-3) where T(R) and taum are the glow peak recording duration and the maximum value of the free carrier lifetime, respectively. This relation between T(R) and taum is useful in finding the approximate value of taum. The value of taum being a function of the concentration and cross section of the TL related centres, one may be able to assess these basic parameters from the study of TL glow curves. The theoretical results are discussed in the perspective of LiF (TLD-100).

Research paper thumbnail of Theoretical Models of Thermoluminescence and Their Relevance in Experimental Work

Radiation Protection Dosimetry, 1999

ABSTRACT TL glow peaks are computed for different models by varying the input parameters. The phy... more ABSTRACT TL glow peaks are computed for different models by varying the input parameters. The physical models considered consist of (1) one trap and one recombination centre (RC), (2) multi-trap non-interactive and (3) multi-trap interactive schemes. The characteristics of these glow peaks are discussed in the perspective of the experimental glow curve properties, namely the effect of dose on temperature of glow peak maximum, on shape of the glow curve and supralinearity of response. The results obtained lead to the following conclusions: (1) The glow peak properties of the one trap one RC system, the multi-trap non-interactive system and the so-called general order do not generally tally with those observed in experimental samples. (2) The multi-trap interactive scheme is capable of producing glow peaks whose characteristics match with the experimental properties.