In this paper, we report on electron microscopy studies of single crystals of the natural mineral lorándite, TlAsS 2 . The main focus of this investigation was to address the question as to whether those lorándite crystals are chemically and structurally homogeneous, in order to be utilized as an effective neutrino detector within the lorándite experiment (LOREX) project. Apart from few secondary minerals, being present only at the surface of the lorándite samples, scanning electron microscopy (SEM) indicated homogeneous crystals. Similarly, transmission electron microscopy (TEM) imaging revealed a homogenous and undisturbed crystal structure, with the only exception of local coffee-bean contrasts; however, rarely observed. These specific contrast variations are known to be a typical strain indicator caused by a local deformation of the crystal lattice. Energy-dispersive X-ray spectroscopy (EDS) in conjunction with electron energy-loss spectroscopy (EELS) did not show any significant chemical difference when analysing regions on or off those coffee-bean features, indicating a chemically homogenous mineral. Since the presence of lattice disturbing secondary phase precipitates could be excluded by imaging and complementary chemical analysis, crystal defects such as dislocations and stacking faults or minor fluid inclusions are discussed as the probable origin of this local elastic strain. The experimental results confirm that the studied lorándite single crystals fulfil all structural and chemical requirements to be employed as the natural mineral that allows to determine solar neutrino fluxes. In addition, critical issues regarding the rather challenging sample preparation of lorándite are reported and a quantification of the maximum tolerable electron dose in the TEM is presented, since lorándite was found to be sensitive with respect to electron beam irradiation. Furthermore, the limits of EDS measurements due to peak overlapping are shown and discussed utilizing the case of Pb in lorándite. In this regard, a comparison with the Tl- and Pb-containing natural mineral hutchinsonite, TlPbAs 5 S 9 , is also included.

中文翻译：

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对马其顿Allchar的矿质钙锰矿（TlAsS2）进行电子显微镜检查

在本文中，我们报告了天然矿物绿铁矿TlAsS 2单晶的电子显微镜研究。这项研究的主要重点是解决那些钙锰矿晶体是否在化学和结构上均一的问题，以便在钙锰矿实验（LOREX）项目中用作有效的中微子检测器。除了极少数次生矿物质（仅存在于褐铁矿样品表面）外，扫描电子显微镜（SEM）显示出均质晶体。类似地，透射电子显微镜（TEM）成像显示出均匀且不受干扰的晶体结构，唯一的例外是局部咖啡豆对比。但是，很少观察到。已知这些特定的对比度变化是由晶格的局部变形引起的典型的应变指示器。能量色散X射线光谱法（EDS）与电子能量损失光谱法（EELS）结合使用时，在分析咖啡豆特征上或附近的区域时，没有显示出任何明显的化学差异，表明该矿物是化学均质的。由于可以通过成像和互补化学分析排除晶格扰动的第二相沉淀物的存在，因此讨论了诸如位错和堆垛层错或少量流体夹杂物等晶体缺陷，作为该局部弹性应变的可能来源。实验结果证实，所研究的钙铝榴石单晶满足了所有结构和化学要求，可以用作确定太阳中微子通量的天然矿物。另外，由于发现了氯铝锰矿对电子束辐照敏感，因此报道了有关氯铝锰矿样品制备颇具挑战性的关键问题，并给出了在TEM中最大可耐受电子剂量的定量分析。此外，显示和讨论了由于峰重叠而导致的EDS测量的极限，并利用了绿锰矿中Pb的情况。在这一点上，还包括与含Tl和Pb的天然矿物钙钠钠长石TlPbAs 5 S 9的比较。由于发现氯铝石对电子束辐照很敏感，因此报道了与氯铝石样品制备相当具有挑战性的关键问题，并给出了在TEM中最大可耐受电子剂量的定量分析。此外，利用峰铁矿中铅的情况，显示并讨论了由于峰重叠而导致的EDS测量的极限。在这一点上，还包括与含Tl和Pb的天然矿物钙钠钠长石TlPbAs 5 S 9的比较。由于发现氯铝石对电子束辐照很敏感，因此报道了与氯铝石样品制备相当具有挑战性的关键问题，并给出了在TEM中最大可耐受电子剂量的定量分析。此外，显示和讨论了由于峰重叠而导致的EDS测量的极限，并利用了绿锰矿中Pb的情况。在这一点上，还包括与含Tl和Pb的天然矿物钙钠钠长石TlPbAs 5 S 9的比较。