Identification of ESR centers and their role in the TL of natural salt from Lluta, Peru

https://doi.org/10.1016/j.apradiso.2022.110126Get rights and content

Highlights

  • The TL glow curve of natural NaCl sample exhibits five peaks.

  • Defect centers were identified in gamma irradiated phosphor due to O ion and F center.

  • The ESR signal due to O ion is associated to the 260 °C TL peak.

  • The ESR signal due to F center is associated to the 128 °C TL peak.

Abstract

In this study, the thermoluminescence (TL) properties of natural NaCl from Lluta, Arequipa-Peru was investigated. The number of peaks and the kinetic parameters associated with the TL glow peaks of NaCl sample after gamma-irradiation were analyzed by initial rise and deconvolution method. Defect centers induced in pure salt by gamma irradiation have been studied by electron spin resonance (ESR) with a view to identify the centers associated with the TL process in the salt. Thermal annealing experiments indicate the presence of three defect centers. Center I characterized by the g-value 2.011 is identified as an O ion and relates with the dominant TL peak at 220 °C. Center II with a g-value of 2.0058 is attributed to a F center and is found to correlate with the 128 °C TL peak. Center III has of g-value 2.014 and is also assigned to an O ion.

Introduction

A considerable number of pure and doped natural and synthetic crystals produced by different synthesis techniques exhibit thermoluminescence (TL) properties. Natural crystals of well-determined TL glow peaks are promising candidates for applications in radiation dosimetry. Among the readily available natural crystals is sodium chloride (NaCl). Depending on its origin, some natural crystals have good TL properties and can therefore be used as a radiation dosimeter.

The TL properties of natural sodium chloride from different sources were investigated by different researchers (Khazal and Abul-Hail, 2010; Spooner et al., 2011, 2012; Rodriguez-Lazcano et al., 2012; Datz et al., 2016; Abdel-Wahed et al., 2016; Mehrabi et al., 2017; Ademola, 2017; Roman-Lopez et al., 2018; Wahib et al., 2020). Recently, the kinetic characterization of thermoluminescence of NaCl has been studied in different regions in the world (Druzhyna et al., 2016; Elashmawy, 2018; Azim et al., 2020; Khamis and Arafah, 2021; Ahmad et al., 2021). In NaCl collected from Khewra salt mines in Pakistan, Ahmad et al. (2021) have stated that the glow curve has two peaks around 115–130 °C and 150–170 °C, and an intense TL peak centered around 220–240 °C, which has been used for radiation dosimetry, due to its high sensitivity to gamma radiation in the range of 5 mGy–100 mGy. The same authors determined the activation energy, frequency factor and kinetic order values for the TL peaks of salt granules by the CGCD method.

Many dosimetric characteristics of TL materials mainly depend on kinetic parameters quantitatively describing the trapping-emitting centers responsible for the TL emission. Thus, the determination of the kinetic parameters is an active area of research. There are various methods for evaluating the trapping parameters from TL glow curves (Chen and McKeever, 1997; McKeever, 1985), which may be broadly classified as methods applied to single or highly isolated glow peaks, and methods applied to complex glow curves. Some methods as the initial rise, variable heating rates and peak shape are suitable for the single or highly isolated glow peaks. Thermal annealing and computerized glow curve deconvolution are methods suitable for the complex glow curves. The first is to isolate each individual TL peak from the others using partial thermal annealing treatment (Borbón-Nuñez et al., 2014) and the other is to make a complete glow curve analysis using deconvolution (Kitis et al., 1998; Benavente et al., 2019).

The aims of many studies are to investigate the possibility of employing these crystals for dosimetry purposes or to understand the trap structure and defects in the materials.

The defect centers created by ionizing radiation are responsible for TL emission. The identification and characterization of irradiation-induced defects in these materials is necessary to elucidate the charge transfer mechanisms during the TL phenomenon. The complete information concerning the charge traps in the TL mechanism cannot be acquired by carrying TL measurements alone. In this context, there is ESR technique, which can be helpful to find more information about paramagnetic species such as charge traps (trapped hole or an electron). In general, the ESR technique provides a non-destructive way to obtain information about possible centers responsible for TL emission through correlation studies between TL and ESR techniques.

The physical basis of the TL signal in the NaCl crystal has been discussed by some authors in the framework of the role of color centers, especially the F-center. Gartia (2009) has studied the feasibility of thermal annealing of F-centers correlated to all TL peaks in the TL glow curve of NaCl. However, there is no record of a correlation study between TL and ESR to identify the centers responsible for TL light emission in natural salt samples.

The objective of this work is focused on the identification of the point defects responsible for the TL emission of Lluta natural salt from Arequipa, Peru. Further, the study aims to determine the kinetic parameters associated with the TL peaks, such as activation energy, frequency factor and kinetic order of each peak at room temperature.

Section snippets

Experimental details

The natural salt sample investigated in this work was collected at the Lluta mine, Arequipa, Peru. This mine is located at the intersection of the following geographic coordinates: latitude 15°58′45.75″ S and longitude 71°59′24.84″ W.

The salt sample from Lluta (SLL) was cleaned and then crushed using a mortar and turned into a fine powder of grain size between 75 and 150 μm for TL and ESR measurements, while grains smaller than 75 μm in diameter were used in structural analysis and chemical

Results and discussion

X-ray diffraction studies are used to reveal the nature of the crystallinity of the as-received (SLL-AR) sample and the sample heat-treated at 500 °C (SLL-TT500). The powder XRD patterns of both samples (SLL-AR and SLL-TT500) are shown in Fig. 1. They are in a good agreement with the NaCl reference pattern and clearly confirm the purity of their crystalline phase. Rietveld refinement analysis of the XRD pattern indicates the presence of the halite crystalline phase and a small concentration of

Conclusions

The XRD, XRF, TL and ESR spectra have been measured for the salt of natural NaCl from Lluta, Arequipa-Peru. XRD pattern of the natural salt sample with or without heat pretreatment revealed the presence of two crystalline phases, being predominant the phase due to Hyalite, and a lower percentage phase due to anhydrite. Samples irradiated with gamma dose show four TL peaks, a main intense peak at 220 °C and three low intensity peaks at 120, 160 and 270 °C. The TL intensity as a function of dose

CRediT authorship contribution statement

Darwin J. Callo-Escobar: Investigation, Conceptualization, Methodology. Nilo F. Cano: Writing – original draft, Supervision, Funding acquisition, Conceptualization, Project administration, Writing – review & editing. T.K. Gundu Rao: Writing – original draft, Validation, Investigation, Visualization. Carlos D. Gonzales-Lorenzo: Methodology, Validation. Klinton V. Turpo-Huahuasoncco: Investigation. Yolanda Pacompia: Investigation. Monise B. Gomes: Investigation, Methodology. Jose F. Benavente:

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The authors would like to express thanks to Ms. E. Somessari from the Institute for Energy and Nuclear Researches (IPEN), Brazil, for kindly carrying out the gamma irradiation of the samples. This work was carried out with financial support from UNSA-Investiga, Peru (Process number IBAIB-02-2018-UNSA). The authors are greatly indebted to Dr. B.C. Bhatt, ex Bhabha Atomic Research Center, Trombay, Mumbai, India.

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