Neste trabalho faz-se uma analise 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 Tm; as armadilhas rasas (ARA), cujos picos TL ocorrem em T

Title in English

Model of traps and interactive recombination centers of thermoluminescence compared to experimental data and theoretical conditions.

Keywords in English

Condensed matter
Thermoluminescence

Abstract in English

Theoretical analysis of thermoluminescence (TL) glow curves and TL intensity as function of radiation dose was carried out using the so called System of lnteractive Multi­ Traps (SIMT). In this model, interaction between different traps and different recombination centers during heating process for TL reading is considered. Thermally active traps (TAT) that give rise to TL peaks at temperature Tm, shallow traps (ST) with peak temperature Tm are the participating traps. Recombination centers, also, take part in the TL emission. Shallow traps are shown not to contribute, however, deep traps contribute in two senses: (i) through charge neutrality, (ii) they can capture charge carriers liberated during TL readout stage. Deep traps are, on the other hand, stable at TL readout temperature, hence, they are named thermally disconnected deep traps (TDDT). Although, there can be traps and recombination centers of different depths, without loss of generality only one kind of TDDT and one kind of CR are here considered in the numerical or analytical calculation. Several parameters are involved in the thermoluminescence: activation energy E, frequency factor s and pre-exponencial factor s' , kinetic order b, concentration of filled or non filled traps and recombination centers, capture cross section of traps and recombination centers and velocity v of free carriers during their transportation. The process of TL emission, involving above parameters, is described by a set of differential equations called rate equations, starting from liberation of charge carriers from traps until their capture by recombination centers. Passing through conduction band is an important step in the process. There has been a wide discussion on approximation called Quase­ Equilibrium (QE) connected with the population of free carriers in conduction band during readout process. Such approximation enables one to obtain from the rate equations, analytical expression for TL intensity. Here, the rate equations within the trame of SIMT were solved numerically using Runge-Kutta method and detailed comparison was performed to discuss under which conditions QE conditions are valid. The supralinearity found in most of actual TL phosphors is satisfactorily explained assuming interactive deep traps, which can capture free charges liberated by TAT traps. lnitially, it was believed that the supralinearity is induced during the irradiation of the TL crystal. Experimental evidences were then found that a same center responsible for TL emission and optical absorption presented a linear growth with dose shown by its optical absorption band.

 

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Publishing Date

2014-02-18

 

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