An Overview on Peak Shape Method for Thermoluminescence Glow Curve Analysis: Application on Tremolite and Actinolite Glow Peaks

An Overview on Peak Shape Method for Thermoluminescence Glow Curve Analysis: Application on Tremolite and Actinolite Glow Peaks

Sukhamoy Bhattacharyya (Acharya Prafulla Chandra College, India) and Partha Sarathi Majumdar (Acharya Prafulla Chandra College, India)
Copyright: © 2018 |Pages: 27
DOI: 10.4018/978-1-5225-5170-6.ch002

Abstract

The shape of a thermoluminescence (TL) glow curve has fundamental importance for calculating the characteristic parameters of trap levels within the band gap. TL analysis are mostly based on the three-parameter general order kinetics model. The parameters are activation energy, order of kinetics, and frequency factor. Peak shape method is one of the most prominent methods for extracting the activation energy from a TL curve. An overview of different peak shape methods along with an alternative approach formulated directly from basic TL equations is presented in this chapter. Generally, peak shape method requires prior knowledge of order of kinetics to determine activation energy which creates a difficulty due to the non-uniqueness of symmetry factor for a particular value of order of kinetics. A modified version of peak shape method which is free from this constraint is discussed here. Activation energies from experimental curves of tremolite and actinolite are estimated using peak shape method. Limitation of peak shape method for saturated TL peaks with heavy retrapping is also discussed.
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Introduction

Thermoluminescence (TL) is a phenomenon of light emission when a material (a semiconductor or an insulator) is heated after being exposed to some ionizing radiation such as X-ray, γ-ray, UV light etc. Impurities and structural defects present in the solids create localized energy levels in the band gap. Energy levels nearer to the conduction band (CB) are potential electron traps whereas those close to valence band (VB) are potential hole traps functioning as recombination centres. In practice, a TL material should have the traps deep enough to be stable at room temperature so that the emission is predominantly in the visible region. Over the last few decades many TL materials have been investigated and developed. The most important application of TL is in the field of radiation dosimetry, including environmental aspects. Moreover, TL has also got very important application in dating where it plays a role complementary to radiocarbon dating.

The theoretical studies of thermoluminescence are based on some models which are mainly phenomenological. The simplest and most widely used theory of TL analysis is based on three important parameters viz. i) activation energy (E), ii) frequency factor (s) and iii) order of kinetics (b). These parameters are also important in indicating the applicability and usefulness of a TL material. These parameters may be extracted by analysing the TL glow curve which is the plot of intensity (I) of emitted light vs. temperature (T).

One of the most successful models for TL analysis is the General Order Kinetics (GOK) model (May & Partridge, 1964; Chen, 1969a) where TL intensity is directly expressed as a function of temperature and involves E, s and b. The GOK model yields the first order equation of Randall & Wilkins (1945) for b → 1 and the second order equation of Garlick & Gibson (1948) for b = 2. Moreover, based on the band picture of solids, there are other models also such as One Trap One Recombination centre (OTOR), Non-interactive Multitrap System (NMTS), Interactive Multitrap System (IMTS) etc. (Pagonis, Kitis & Furetta, 2006). These models are mathematically expressed in terms of differential equations governing the trafficking of charge carriers. In OTOR model, the existence of one trap and one recombination centre is assumed within band gap whereas in NMTS and IMTS models, multiple trap levels including thermally disconnected deep traps (TDDT) are also considered.

There are various techniques to determine the trapping parameters of a TL curve (Chen & Pagonis, 2011; Chen & McKeever, 1997). The most commonly used methods are (i) Peak Shape (PS) method, (ii) Various Heating Rates (VHR) method, (iii) Initial Rise (IR) method, (iv) Area method, (v) Computerised Glow Curve Deconvolution (CGCD) technique etc. This review focuses on the applicability of peak shape method for determining the activation energy from a TL glow curve. Peak shape method is widely used in TL studies and is primarily based on the geometric shape of the glow curve which is governed by the trapping parameters. Along with theoretical considerations, experimental TL curves of tremolite and actinolite materials belonging to silicate minerals group that are found in abundance in the crust of earth have also been studied in the light of peak shape method for extracting the activation energies that are useful to interpret the TL mechanism in these materials. The plan of the article is as follows: a brief review of the prominent works on peak shape method is discussed in section 2; the mathematical formulation of peak shape method is elaborated in section 3; the application of peak shape method to analyse the experimental TL curves of tremolite and actinolite is given in section 4; the limitations of peak shape method in case of saturated TL peaks with heavy retrapping discussed in section 5 and concluding remarks are summarized in section 6.

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