Thermoluminescence (TL) response of naturally occurring Eocene rock salt (Gray halite) is assessed for its potential use as a cost-effective phosphor for dosimetric applications. Natural deposits of the Eocene salt lie on the Himalayan foothills in Pakistan. The grayish color of the halite is due to the intermixing of black bitumen/shale. EDS and ICP-OES techniques are used for the analytical study of the sample. It confirms the presence of Ca, K, Mg, Sr, Zn SO, Mn, Al, Si and Fe along with the main matrix-NaCl. The Eocene salt is sulfur (S) rich, and potassium (K) poor mineral as compared to the other regional halite. The XRD analysis shows that lattice structure of the halite is composed of two interpenetrating FCC-sublattices of Na and Cl. Cold pressed pellets weighing 40 mg are produced for dosimetric study of the material. Standard gamma source is used for pellet irradiaition. Three different samples of Eocene salt (i.e. rock salt, naturally precipitated salt and refined salt) are prepared. It is observed that, if the material is used as such in its natural form, the dosimetric peak of the glow curve occurs at higher temperature >260 °C. The raw form of rock salt is therefore pre-processed (refined) whereby the major glow peak has shifted onto the dosimetrically significant position at 230 °C. Because of the optimal shape of the glow curve, the refined salt sample is investigated in detail: TL glow curves are acquired from 50 °C to 300 °C, the phosphor reveals a composite glow curve where four peaks are observed at approximate positions of 110 °C (P1), 145 °C (P2), 180 °C (P3) & 230 °C (P4). TL response is studied in the range of 5 mGy to 2 Gy; where a linear/superalinear dose-response behavior is observed for the current material. The Minimum Detectable Dose Limit (MDDL) is measured from the linear region and found to be 0.37 mGy. The first readout results in very low residues <0.005 % and is sufficient to afresh the dosimeter for the next reading. A repeatability test is performed up to 20 identical cycles: the resultant COV, obtained for refined salt sample, is 2.3 % (and 1.5 % in 10 cycles). The irradiated pellets show about 20 % loss of the initial signal for one month fading study. T-T method and CGCD techniques are used for kinetic analysis. Kinetic parameters (b, E and s) are estimated from multiple glow curves and found similarities in the results. The results of the preliminary investigations suggest that the pellet prepared from Eocene salt has a potential for use in TL dosimetry.

中文翻译：

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巴基斯坦巴哈杜尔凯勒遗址开采的始新世岩盐（灰色岩盐）的热释光剂量特征和辉光曲线分析

天然存在的始新世岩盐（灰岩盐）的热释光（TL）响应被评估其作为剂量测定应用中具有成本效益的磷光体的潜在用途。始新世盐的天然矿藏位于巴基斯坦的喜马拉雅山麓。岩盐的浅灰色是由于黑色沥青/页岩的混合造成的。 EDS 和 ICP-OES 技术用于样品的分析研究。它证实了 Ca、K、Mg、Sr、Zn SO、Mn、Al、Si 和 Fe 以及主要基质 - NaCl 的存在。与其他地区的岩盐相比，始新世盐富含硫 (S)，而钾 (K) 贫乏。 XRD分析表明，岩盐的晶格结构由Na和Cl两个互穿的FCC亚晶格组成。生产重 40 毫克的冷压颗粒用于材料的剂量测定研究。标准伽马源用于颗粒辐照。制备三种不同的始新世盐样品（即岩盐、自然沉淀盐和精制盐）。据观察，如果材料以其自然形式使用，则辉光曲线的剂量峰值出现在 >260 °C 的较高温度处。因此，岩盐的原始形式经过预处理（精炼），主要辉光峰已转移到 230 °C 的剂量学显着位置。由于辉光曲线的最佳形状，对精制盐样品进行了详细研究：从 50 °C 到 300 °C 获得了 TL 辉光曲线，荧光粉显示了一条复合辉光曲线，其中在大约 110 的位置观察到四个峰值°C (P1)、145 °C (P2)、180 °C (P3) 和 230 °C (P4)。研究了 5 mGy 至 2 Gy 范围内的 TL 响应；其中观察到当前材料的线性/超线性剂量响应行为。从线性区域测量最小可检测剂量限值 (MDDL)，结果为 0.37 mGy。第一次读数产生的残留量非常低，<0.005%，足以刷新剂量计进行下一次读数。重复性测试最多执行 20 个相同的循环：精制盐样品获得的最终 COV 为 2.3%（10 个循环中为 1.5%）。经过一个月的衰落研究，经辐照的颗粒显示初始信号损失约 20%。采用TT法和CGCD技术进行动力学分析。根据多个辉光曲线估算动力学参数（b、E 和 s），并发现结果相似。初步研究结果表明，由始新世盐制备的颗粒具有用于 TL 剂量测定的潜力。