Gamma-ray absorbing characteristic of obsidian rocks as a potential material for radiation protection

https://doi.org/10.1016/j.radphyschem.2022.110309Get rights and content

Highlights

  • Gamma-ray absorption properties and radioactivity of obsidians were investigated.

  • Theoretical absorption coefficients were calculated with WinXCOM to compare.

  • High absorption with small half-value thicknesses in the samples were revealed.

  • The radioactivity of the samples is well below the acceptable limits.

  • Obsidian can be used as a potential gamma-ray absorber material in a various areas.

Abstract

In this study, natural radionuclide levels and mass absorption coefficients of obsidian samples were examined to determine their gamma radiation properties. Fourteen obsidian samples were collected from 7 different locations in Rize province, İkizdere region, Turkey. X-ray fluorescence measurements of the samples revealed the silica structure and comparable elemental structure with slight differences in atomic ratios. Radionuclide analysis showed that the 137Cs activity was below the detection limit, and the mean activities of 238U, 232Th and 40K were 93 ± 9, 67 ± 7, 1027 ± 19 Bq.kg−1, respectively. The average experimental mass absorption coefficients at 81.0 keV, 302.9 keV, 356.0 keV and 661.7 keV were found to be 0.216, 0.108, 0.098 and 0.080 cm2 g−1, respectively. In the <100 keV region which the photoelectric effect is dominant, differences among the absorption coefficients were more pronounced, while it was relatively much smaller in the intermediate energy region. Also, it was seen that the absorption coefficients of the samples were higher than many materials, especially in the low energy region. The average half-value thicknesses showed that obsidian between 1.43 cm and 3.84 cm depending on the photon energy should be used to halve the radiation intensity. In addition, it was determined that the thicknesses in the range of 4.75 cm–12.76 cm were sufficient to reduce the intensity to one tenth. Considering all the analysis results, it can be said that obsidian is a potential material in radiation protection and its absorption properties can be improved by processes such as elemental doping.

Introduction

Obsidian rock (also known as volcanic glass) was formed by sudden cooling of viscous, silicon-rich magma emerging from the earth (Galoisy and Calas, 2021). It has properties such as a hardness level of 5–6 on the Mohs scale and fracture in conchoidal form. Recently, they have been used in landscape architecture, furniture accessories, cosmetic products, and medicine surgery (Cotterell and Kamminga, 1992; Demir, 2017; Kücük and Gezer, 2017). Obsidians which can exist in black, brown, green and mixed translucent colors due to their mineral diversity, exhibit strange optical properties such as light diffraction and iridescence (Dolan and Shackley, 2017; Ma et al., 2001, 2007). They are found in many regions of the world such as the United States, Mexico, Turkey, etc. (Ambroz et al., 2001; Bıgazzı et al., 1997; Holmes, 1900; Neri, 2007). However, Turkey is especially a very rich country in terms of obsidian ore reserves. In Turkey, it is mined black obsidian in Van-Erciş and Artvin regions, green obsidian in Nemrut Mountain and Tatvan region and red obsidian in Rize-İkizdere region. Besides, obsidian ores were also found around Kars, Ağrı Mountain and Pasinler. Apart from these, obsidians stand out for their mineral richness. They were found intense iron minerals in Hasan Mountain obsidian ore and gold minerals in İkizdere obsidian ore (Kücük and Gezer, 2017).

Humans are continuously exposed to natural cosmic radiation from the sun and radioactive materials in varying quantity since the formation of the earth. In addition to these natural radiations, they are also exposed to artificial radiation sources originating from applications such as nuclear and radiation physics, industry, biology, medicine. Radiation has some benefits, especially in the cancer treatment and in the treatment of certain biological problems. However, the harmful effects caused by radiation on human health are known. Considering all these, since radiation-related risks are always present in human life, it is necessary to take protective measures to minimize these risks (Radiation, 2017; Trapp and Kron, 2008).

There are three basic ways to protect from radiation. These are distance, time and shielding. Among these, shielding is the most important factor of radiation protection. Shielding is based on placing a radiation absorbing material between the protected system and the radiation source. Lately, radiation shielding materials are of great interest due to the exposure to ionizing radiation in applications such as industrial, space, medicine, accelerator plant and nuclear power plants (Aygun et al., 2021).

The most important feature for the material to be used for the shielding is the ability of that material to absorb radiation. High-density materials are more suitable for protection against the destructive impact of radiation (Luković et al., 2015). However, low-density materials can be used by increasing the material thickness to decrease the radiation intensity (AbuAlRoos et al., 2019). In this context, parameters such as mass attenuation coefficients, half-value and tenth-value thicknesses gives important information about the radiation protection properties of materials (Baltas et al., 2019; Lakshminarayana et al., 2018). In addition, the evaluation of the radioactivity capabilities of shielding materials is another important factor for the application areas.

The absorption coefficients can be calculated theoretically with a computer code such as WinXCOM. This code developed by the Berger and Hubbell calculates attenuation coefficients and photon cross sections for elements, compounds and mixtures in the energy range 1 keV–100 GeV (Berger and Hubbell, 1987). Experimental studies have also been carried out to determine the characteristics of some materials used for shielding in the form of element (e.g. Pb, C), compound (e.g. Bi2O3, PbO, MoO3, C15H16O2) and mixture (Bhosale et al., 2016; İçelli et al., 2013; McCaffrey et al., 2007; More et al., 2021; Sayyed et al., 2018, 2019, 2021a, 2021b; Un and Sahin, 2011). Besides these materials, there are also studies examining of the radiation absorption properties of many building materials and rocks such as cement, concrete, gypsum, marble, basalt, granite, granite, limestone, etc. (Akkurt et al., 2012; Eke et al., 2017; Medhat, 2009; Nimet and Hatıpoglu, 2018; Obaid et al., 2018a, 2018b). In some studies, radioactivity levels of building materials and some rocks were investigated (Beretka and Matthew, 1985; Cengız et al., 2019; Dong et al., 2022; Örgün et al., 2007; Righi and Bruzzi, 2006; Sonkawade et al., 2008; Veiga et al., 2006). While obsidian rocks used as shielding material occupy a very important place with superior properties, research on the radiation-related properties such as absorption coefficient and radionuclide analysis of obsidian is quite limited (Aygun et al., 2021; Chiozzi et al., 2000). In a study on İkizdere obsidian, the samples were examined in terms of mineralogical, petrographic, geochemistry and fission-track dating (Yeğingil et al., 2002). In a study including İkizdere obsidians, the structural and morphological properties of the samples as well as theoretical radiation shielding potentials were examined (Aygun et al., 2021). It was stated that there is a small amount of crystal phase in obsidian and these phases contain less than 1% water (Ercan et al., 1989). It was revealed that obsidian found in the İkizdere region can be used as a pozzolana material in cement (Ustabaş and Kaya, 2018).

As stated above, although some studies have been carried out on some properties of İkizdere obsidians. The aim of this study is to examine the radiational properties of İkizdere obsidian, which is likely to be used as a radiation shielding material. In this context, gamma-ray absorption coefficients (81 keV–662 keV), half-value thicknesses and tenth-value thickness of the obsidians mined from different locations in İkizdere region were determined. However, to compare the absorption coefficients which is one of the crucial parameters in shielding, theoretical absorption coefficients by WinXCOM code were also calculated. Besides, radionuclide analysis (for 238U, 232Th and 40K) were also performed to reveal the level of radioactivity in the region where the samples were extracted.

Section snippets

Study area

The sample collection stations are shown in Fig. 1. The Eastern Pontides which are one of Turkey's tectonic and geological associations are divided into three separate regions as the North Zone, the South Zone and the Axis Zone, taking into account their structural and lithological features (Arslan et al., 1997; Eyuboglu, 2006; Özsayar et al., 1981). Our study area is located in the Northern Zone. The oldest unit in the study area is late Cretaceous-aged Çağlayan formation consisting of basalt,

Radionuclide analysis of the samples

The gamma-ray (γ) activity associated with natural radioactive isotopes is conducted by their amount in the ecosystem, average lifetime, and chemical-physical properties (Chiozzi et al., 2001). Since γ-activity can cause harmful exposure to human health, it is important to know the radioactivity values of the materials used in applications. Radionuclide analysis of 14 obsidian rocks collected from 7 different locations was performed by gamma spectroscopy. 238U, 232Th, 40K radioactivities, their

Conclusion

In this study, radionuclide and absorption properties of 14 İkizdere Obsidian samples collected from 7 different locations were investigated. In this way, information was obtained about the use of these rocks as a potential radiation shielding material. Chemical analyzes were carried out with XRF spectroscopy to determine the elemental distributions of obsidian rocks. Radionuclide analysis of the obsidians was performed using the HPGe radiation detector. Experimentally, the absorption

Author statement

Selcen Uzun Duran: Methodology, Collection and preparation of samples, Calculations, Writing - original draft, Belgin Küçükömeroğlu: Conceptualization, Collection and preparation of samples, Writing - review & editing, Ali Çiriş: Measurements, Preparation of samples, Writing - review & editing. Hakan Ersoy: Mapping, Collection of samples Writing - review & editing.

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.

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