Applications of X-ray synchrotron microtomography for non-destructive 3D studies of paleontological specimens

Paleontologists are quite recent newcomers among the users of X-ray synchrotron imaging techniques at the European Synchrotron Radiation Facility (ESRF). Studies of the external morphological characteristics of a fossil organism are not sufficient to extract all the information for a paleontological study. Nowadays observations of internal structures become increasingly important, but these observations should be non-destructive in order to preserve the important specimens. Conventional microtomography allows performing part of these investigations. Nevertheless, the best microtomographic images are obtained using third-generation synchrotrons producing hard X-rays, such as the ESRF. Firstly, monochromatisation avoids beam hardening that is frequently strong for paleontological samples. Secondly, the high beam intensity available at synchrotron radiation sources allows rapid data acquisition at very high spatial resolutions, resulting in precise mapping of the internal structures of the sample. Thirdly, high coherence leads to additional imaging possibilities: phase contrast radiography, phase contrast microtomography and holotomography. These methods greatly improve the image contrast and therefore allow studying fossils that cannot be investigated by conventional microtomography due to a high degree of mineralisation or low absorption contrast. Thanks to these different properties and imaging techniques, a synchrotron radiation source and the ESRF in particular appears as an almost ideal investigation tool for paleontology. PACS 01.30.Cc; 07.05.Hd; 68.37.Yz; 29.20.Lq; 81.70.Tx     

The Elgin marvel: using magnetic resonance imaging to look at a moldic fossil from the Permian of Elgin, Scotland, UK

The successful use of magnetic resonance imaging (MRI) of a moldic fossil dicynodont from the Permian aeolian Hopeman Sandstone Formation of Elgin, Scotland, UK, provides paleontologists with a nondestructive technique for examining fossils preserved in this fashion. For large moldic fossils, medical scanners such as the Phillips Gyroscan MRI, provide adequate resolution for gross morphologic determination. The 3-D rendered images using software such as Philips Easivision allows the fossil to be examined and dissected without causing any physical damage to the original material. From the scans it is also possible to produce 3-D stereolithographs for a more tactile manipulation of the renderings.     

SXRF分析恐龙脊椎头化石微量元素

利用同步辐射X射线荧光成像方法(SXRF)检测了二件不同地区的脊椎头恐龙化石,在每件化石截面上的二个不同区域分别获取了8种元素的分布图及其荧光光谱。在两件样品靠外层的骨密质部位,发现有较密集的稀土元素Y(钇)。在姜驿恐龙化石中Y的富集,来自于化石的成岩过程,在元素分布图中与稀土元素Y共生的含Ca化合物是氟磷酸钙。武定田心恐龙脊椎头化石中,在稀土元素钇的富集的区域,其它元素包括Ca的含量均特别少。此种稀土元素的富集可能是由于化石中含有分解不完全的有机物的吸附所致。在姜驿恐龙脊椎头化石中,微量元素Mn、Fe和Al属于共生矿物;As、Sr、Y元素集中分布在化石的外边缘处,也是三者共生。在田心恐龙脊椎头化石中,微量元素Mn、Fe和Al属于共生矿物,Sr、Y元素共生,Cu元素的分布相对集中。研究表明,恐龙化石中矿物的元素含量及其分布与骨骼所属的部位无关,只与源地有关。恐龙化石中稀土钇富集的地方,呈现白色。同步辐射X射线荧光探测法,能原位、快速、无损地检测出化石样品各种元素的荧光光谱,给出恐龙化石元素分布的二维信息,对于分析恐龙化石所蕴含的侏罗纪时期的古地质特征和古生物信息,给出了重要的依据。     

自贡地区恐龙骨骼化石及围岩特征的研究

自贡地区恐龙化石埋藏丰富、分布广泛、保存完整,具有重要的科学价值、社会价值和经济价值。用X荧光衍射研究自贡恐龙骨骼化石及围岩元素组成,XRD结合红外光谱仪分析确定化石的矿物组成,化石切片和显微观察了解骨骼内部构造和填充物质。恐龙骨骼化石及围岩中的含钙量均较高(5%),但化石含钙量达到30%以上;化石中的含硅量较低(0.24%—1.45%),围岩中的含硅量较高(14%);化石中的含磷量为围岩的46倍以上。化石的主要化学成分是碳氟磷灰石,其次是碳酸钙;围岩的主要成分是二氧化硅。实验结果可为恐龙化石的鉴别及保护材料的研制提供理论依据。     

珊瑚化石的红外光谱及XRD研究

通过红外吸收光谱和X射线粉晶衍射分析对不同颜色及质地且表面具放射状纹理的珊瑚化石的结构特征及组成物相进行了研究。结果表明,此类珊瑚化石主要由SiO₂组成,内部仍保留了钙质型珊瑚横断面所特有的放射状显微结构,成因属SiO₂交代作用。不同颜色和质地的珊瑚化石红外吸收光谱基本一致,均显示典型的石英质玉的红外吸收光谱特征。XRD分析表明不同颜色和质地的珊瑚化石主要组成物相一致,为SiO₂,其他矿物极微量,且不含CaCO₃。     

同步辐射X射线荧光对双柏恐龙化石的分析

首次使用同步辐射X射线荧光法（SXRF）测试了双柏县安龙堡的恐龙化石,在其截面上原位获得了Ca,Fe,Mn,Cu,Zn,As,Y和Sr等八种元素的分布图。测试结果表明,各种元素在化石中的分布是非均匀的,与一般的矿物岩石元素的分布不同。元素分布图表明,在双柏恐龙化石中未检测到As元素,与四川自贡恐龙由于As元素高的非正常死亡相比,双柏恐龙属正常死亡情形。在分布图中容易看出,化石中的Fe和Mn元素是共生的;Sr和Y两种元素也是共生的,显示化石在成岩过程中,所含Fe,Mn,Sr,Y的化合物胶体均为带异种电荷的颗粒,据此可推知当时这些元素所属化合物的可能形式。同步X射线荧光显微探测法研究恐龙化石元素分布具有原位、快速、准确、直观等优势,它可以将共生元素分离开来,这是XRD和等离子光谱等测试手段不能实现的。恐龙化石微量元素的分布,揭示了化石微区矿物结构的相关信息,这对于挖掘化石蕴涵的古地质特征,恢复古地理、古地质研究的潜力具有重要意义。     

武定恐龙化石的显微拉曼光谱研究

本文首次利用激光显微拉曼光谱、原子光谱和偏光显微镜等方法 ,对云南武定的恐龙化石进行了分析研究。实验发现 ,恐龙化石表面和截面的拉曼光谱 ,均为典型的方解石 (CaCO3 )晶体的拉曼谱 ,并未发现有其他成分的拉曼谱。原子发射光谱的分析结果表明 ,恐龙化石中的主要元素有Ca(>10 % ) ,其次是Si(5 0 % )和P(4 0 % ) ,还有Fe(1 0 % )等 ,但未发现铱、钍等稀有元素。由恐龙化石截面在偏光显微镜下的图像可以知道 ,恐龙化石表面层的成分主要是方解石晶体 ;内部的主要成分为方解石 (CaCO3 )晶体 ,此外还有纤维状一水二氧化硅 (分子式SiO2 ·nH2 O ,属非晶态 )等成分。激光拉曼光谱能快速无损地准确检测出恐龙化石的主要成分是方解石 (CaCO3 ) ,拉曼光谱对恐龙化石的分析结果与原子光谱、偏光显微镜的分析结果是一致的     

古化石与陨石的元素对比分析

古化石是古代的动植物经过漫长地质时期和地质作用形成的化石,它是地球历史的鉴证,记载着地球生态环境演变的信息;长时间遨游于太阳系中的陨石,经过宇宙间的核反应和大气的磨蚀,形成了独特的纹理与造型,记载着外太空形成演化的原始信息。古化石成分的分析是研究地球生物起源和进化的科学依据;而陨石是大自然馈赠的来自外太空的岩石样品,极为珍贵和稀少,对陨石成分的分析可以为我国外星球探测和天体化学的发展提供更好的基础。对样品的溶解方法进行选择和优化,最终以硝酸、氢氟酸、高氯酸为混合试剂,采用微波消解法溶解古化石样品;以王水、硝酸、氢氟酸、高氯酸为混合试剂,采用微波消解与湿法消解相结合溶解陨石样品,应用电感耦合等离子体原子发射光谱法(ICP-AES)测定了3种古化石样品、3种陨石样品中多种元素的含量,并将古化石与陨石中相同元素的含量进行对比。分析结果表明,古化石和陨石中都含有Pb,Hg,Ge,Fe,Ni,Cu,Co和Mn等重金属元素,以及部分稀土元素。该方法加标回收率在98.2%~106%之间,相对标准偏差均小于2.12%。方法的灵敏度高,准确度和精密度好。     

Synchrotron Radiation Tomography for Reconstruction of Layer Structures and Internal Defects of Composite Materials

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不同地区恐龙化石的显微激光拉曼光谱研究

研究了7个恐龙化石样品在较高波数段的显微激光拉曼光谱,化石样品来自不同地区并且属于不同的骨骼部位。显微激光拉曼光谱表明,这7个恐龙化石的拉曼特征峰的峰位十分相似,但峰形有差别。进一步的比较分析还发现,不同源地相同骨骼部位的拉曼峰峰形比较相似,例如不同地区的脊椎头化石图谱比较相似,肢骨头化石的拉曼峰峰形也比较相似。实验结果表明,在1 000～1 800 cm-1波数段内的拉曼特征峰,主要与原骨骼所属的部位有关,与化石的源地关系不太大。785 nm的拉曼光谱不能区分恐龙化石的源地,但可以在较小的地质区域内区分化石骨骼的部位。     

古生物群遗迹化石的三维数字化测量

对古生物化石进行数字化建档,为古生物化石的长久保存、研究和复原提供了一个切实可行的办法。阐述了非接触式激光扫描仪的测量原理,并利用其对罗平古生物化石群中分布在120m2范围内的古生物足迹化石进行了数字化测量,采用大视场WIDE和小视场TELE镜头交替使用的方法获取全场和单一足迹化石三维点云数据,再利用三维数据处理PolyWorks软件将两个镜头的三维数据进行对应的嵌入融合,最终测量结果既能全面记录足迹整体分布,真实反映古生物爬行运动轨迹,又能精细反映足迹局部特征。结果表明提出的对大面积野外待测对象的测量方法,为化石野外测量、三维数字化、数字存储提供了可行方案。     

Raman and FTIR spectroscopy applied to the conservation report of paleontological collections: identification of Raman and FTIR signatures of several iron sulfate species such as ferrinatrite and sideronatrite

Fossil materials that contain iron sulfide are well known for their instability when exposed to oxygen and humidity. This term however combines a great variety of materials showing different types of damages. Most of them consist of crystal efflorescence appearing on the surface and inside the matrix. In this work, a methodology was determined for the analysis of these damages by the use of Raman and infrared spectroscopy. The infrared and Raman signatures of a large set of iron sulfates were characterized. Specific attention was paid to sideronatrite and ferrinatrite, which are two associated sodium/iron(III) sulfates, and their infrared and Raman bands were partially assigned. Analysis performed on a selection of 11 damaged fossils showed a great variety of degradation products: besides one case that appeared to be a synthetic resin close to polyvinylchloride acetate, which was applied with a brush on the fossil surface, all degradation products belong to the sulfate group. However, many iron‐free sulfates, such as gypsum, halotrichite, epsomite, or pentahydrite were found, often in association with iron sulfates. In one case, despite the presence of iron in the matrix, no iron sulfate could be detected. This shows that the term ‘pyritic fossil’, commonly used by collection managers, is not appropriate as it oversimplifies the reality. A name such as ‘sulfide‐containing fossil’ would be more suitable. Copyright © 2012 John Wiley & Sons, Ltd.     

Synchrotron radiation X-ray fluorescence used to studying the migration of chemical elements in biogeochemical food chains

Synchrotron radiation X-ray fluorescence makes it possible to determine the multielemental composition of atmospheric aerosols and other components of biogeochemical chains. From these data, a close interrelation between the concentration of elements in atmospheric aerosols and tissues (liver, bone tissues) of small mammals of the Central Urals and in tissues (hair, bone tissues) of wild animals of Gornyi Altai has been revealed by correlation analysis. A similar interrelation has been established for the elemental composition of atmospheric aerosols and food, the elemental composition of atmospheric aerosols, and other components of biogeocenosis (plants, mushrooms and soil). It is assumed that atmospheric aerosols play an important role in the global cycling of chemical elements.     

Mapping the composition of chondritic meteorite Northwest Africa 3118 with micro-Raman spectroscopy

Meteorites provide precious clues about the formation of planets in the solar system. Here, an analytical method to study chondritic meteorites using low- and high-resolution micro-Raman spectroscopy is presented. An approach in mapping the distribution of mineral compositions of a sample is introduced by measuring ～10⁴ Raman spectra along linear, micron-wide paths that traverse the sample to capture detail on small and large spatial scales (from micrometers to millimeters). To refine these analytical procedures, a well-defined chondrule and surrounding matrix of the carbonaceous chondrite Northwest Africa 3118 are analyzed. The morphology and elemental composition of the sample are also studied using scanning electron microscopy with energy-dispersive X-ray spectroscopy and creating composite maps with the images obtained by these techniques along the same Raman linear path. The Raman line scan maps of this sample show clear spatial segregation of constituents including pyroxene and olivine, both within and outside the chondrule. Graphitic carbon is also present and appears clustered in domains of a few hundred microns both in the matrix and in the central core of the chondrule. The results obtained with the scanning electron microscopy and energy-dispersive X-ray spectroscopy techniques show that iron is most abundant in the matrix surrounding the chondrule, while the chondrule is enhanced in silicon, magnesium, calcium, aluminum, and sodium. These findings provide a detailed identification of the elemental and mineralogical, spatial composition of the analyzed regions of Northwest Africa 3118.     

High‐spatial‐resolution mapping of superhydrophobic cicada wing surface chemistry using infrared microspectroscopy and infrared imaging at two synchrotron beamlines

The wings of some insects, such as cicadae, have been reported to possess a number of interesting and unusual qualities such as superhydrophobicity, anisotropic wetting and antibacterial properties. Here, the chemical composition of the wings of the Clanger cicada (Psaltoda claripennis) were characterized using infrared (IR) microspectroscopy. In addition, the data generated from two separate synchrotron IR facilities, the Australian Synchrotron Infrared Microspectroscopy beamline (AS‐IRM) and the Synchrotron Radiation Center (SRC), University of Wisconsin‐Madison, IRENI beamline, were analysed and compared. Characteristic peaks in the IR spectra of the wings were assigned primarily to aliphatic hydrocarbon and amide functionalities, which were considered to be an indication of the presence of waxy and proteinaceous components, respectively, in good agreement with the literature. Chemical distribution maps showed that, while the protein component was homogeneously distributed, a significant degree of heterogeneity was observed in the distribution of the waxy component, which may contribute to the self‐cleaning and aerodynamic properties of the cicada wing. When comparing the data generated from the two beamlines, it was determined that the SRC IRENI beamline was capable of producing higher‐spatial‐resolution distribution images in a shorter time than was achievable at the AS‐IRM beamline, but that spectral noise levels per pixel were considerably lower on the AS‐IRM beamline, resulting in more favourable data where the detection of weak absorbances is required. The data generated by the two complementary synchrotron IR methods on the chemical composition of cicada wings will be immensely useful in understanding their unusual properties with a view to reproducing their characteristics in, for example, industry applications.     

Atom probe tomography analysis of radiation-induced solute clustering in austenite stainless steels

Various types of defects are produced by the irradiation of energetic particles onto a structural material. The large number of mobile vacancies and self-interstitial atoms during irradiation induce defect fluxes and the diffusion of solute atoms in the matrix. The preferential interaction between the solute atoms and radiation-induced defects leads to the enrichment/depletion or clustering of the solutes at defect sinks. In the current work, atom probe tomography (APT) was used for the analysis of radiation-induced solute clustering in ion-irradiated austenite stainless steel 316. Quantitative analysis of the localised clustering of chemical elements was implemented and a parameter selection procedure was proposed. The number density and size distribution of Si clusters in APT specimens irradiated at various temperatures were examined. At high temperature, the number density of the clusters decreased and their size increased. The localized Si atoms in variously shaped defects were clearly identified. The APT method was demonstrated to be suitable for identifying defect structures and for the quantitative analysis of clustering in irradiated specimens.     

TOF-SIMS analysis of magnetic materials in chum salmon head

A piece of tissue extracted from a chum salmon Oncorhynchus keta head was measured with time-of-flight secondary ion mass spectrometry (TOF-SIMS) in order to evaluate the distribution and composition of magnetic materials in the tissue, which may concern with geomagnetic navigation of long-distance migrating salmon. Several depositions of iron compounds were detected in the tissue by TOF-SIMS analysis. Comparing with total ion images providing a topological tissue structure, specific distribution of iron ion in the tissue was clearly shown. Higher magnification TOF-SIMS analysis revealed the existence of the aggregations of iron particles. Iron oxide clusters comprising many submicron particles were also detected in the tissue using scanning electron microscopy and X-ray analysis, suggesting the common existence of submicron-scale iron oxides in salmon heads. These results suggest that TOF-SIMS analysis is a valid method to clarify detailed structures and chemical properties of candidate magnetoreceptors in fish heads.     

High-resolution non-invasive 3D imaging of paint microstructure by synchrotron-based X-ray laminography

The characterisation of the microstructure and micromechanical behaviour of paint is key to a range of problems related to the conservation or technical art history of paintings. Synchrotron-based X-ray laminography is demonstrated in this paper to image the local sub-surface microstructure in paintings in a non-invasive and non-destructive way. Based on absorption and phase contrast, the method can provide high-resolution 3D maps of the paint stratigraphy, including the substrate, and visualise small features, such as pigment particles, voids, cracks, wood cells, canvas fibres etc. Reconstructions may be indicative of local density or chemical composition due to increased attenuation of X-rays by elements of higher atomic number. The paint layers and their interfaces can be distinguished via variations in morphology or composition. Results of feasibility tests on a painting mockup (oak panel, chalk ground, vermilion and lead white paint) are shown, where lateral and depth resolution of up to a few micrometres is demonstrated. The method is well adapted to study the temporal evolution of the stratigraphy in test specimens and offers an alternative to destructive sampling of original works of art.     

Spectroscopic analyses of an ancient silver fragment of the reliquary bust of St. Leo

A fragment of the silver reliquary bust of St. Leo, made in Messina, Italy, in the last of 1739 and now preserved in the church of SS. Savior of Africo Nuovo, Reggio Calabria, Italy, was investigated with spectroscopic techniques (scanning electron microscopy (SEM)+energy-dispersive X-ray (EDX), X-ray diffraction (XRD)) in order to analyze the composition of the sample in terms of elements and compounds. EDX analysis employs an electron beam that interacts with the sample, leading to the emission of characteristic X-rays as secondary radiation. In the XRD analysis, a Cu Kα X-ray radiation is detected by a Si(Li) solid-state detector after the interaction with the sample. The chemical composition of the bulk allowed to identify the constituting metal alloy, while the detection of surface elements and compounds, closely related to the sample preservation, was useful in order to suggest to restorators the best interventions to minimize the conservation problems that could affect the durability of the precious artefact.