Abstract Computed X-ray tomography is a technique that produces cross sections of an object from a series of projections at different angles. The technique has found widespread use in medical CAT scanners, which typically have resolutions of ~1 mm. Microtomography is the extension of this technique to smaller spatial resolution down to <1 μm. In the last 15 years the development of high-brightness synchrotron X-ray sources, high resolution CCD detectors, and high-performance computing have allowed the field of microtomography to progress rapidly. It is now being applied widely in Earth and soil science, where it is used to image the 3-D distribution of minerals, fluids, and pores. By exploiting X-ray absorption edges, 3-D images of the distribution of specific chemical elements can be produced. This is used to image the distribution of aqueous and organic fluids that have been doped with contrast agents such as iodine and cesium. The method is also being used to locate trace-mineral phases containing high-atomic-number elements such as zirconium and cerium. With fluorescence tomography 3-D images of trace element abundances and even oxidation states can be produced. This is being applied to understand the chemical contamination and remediation by plants in the environment. Diffraction tomography images the 3-D distribution of crystalline phases based on their powder diffraction peaks, and is very useful for imaging materials with similar X-ray absorption and composition but different crystalline structures.

Abstract Scanning electron microscopy (SEM) and its auxiliary technologies have been exploited by various industries for more than 50 years. One of its main applications has been to characterize materials at very high magnification. Recent interest by the petroleum industry to better characterize and understand shale hydrocarbon reservoirs has let to an increased interest in utilizing SEM technology for shale reservoir studies. The purpose of this paper is to review basic SEM operational principles and applications that are particularly useful for characterizing shale hydrocarbon reservoirs.

Abstract Electron microbeam techniques such as Scanning Electron Microscopy (SEM), Electron Probe Microanalysis (EPMA) and Transmission Electron Microscopy (TEM) are commonly used in the characterization of industrial minerals providing morphological, chemical and structural information down to the atomic scale. The principal advantage of the electron microscope over the light microscope is the much improved resolution, due to the very low wavelength of the energetic electron (<1 Å) compared to the visible light, which is employed in the optical microscope. A key advantage of microbeam instruments is the generation of X-rays from the interaction of electron with the sample thereby allowing both the identification of elements present through observation of the KLM X-ray lines and determination of the elemental composition when matrix affects are taken into consideration. In this chapter an overview of the two main classes of electron microscopy, scanning and transmission, is presented, including a description of the instrumentation required and a discussion of their similarities and differences. The chapter also includes detailed information regarding the generation, detection and measurement of the various signals within the SEM and EPMA, the two instrument techniques most common to mineralogists. Finally, several case studies highlighting the use of these two electron microbeam techniques in the characterization of industrial minerals are presented. The examples were chosen to both illustrate traditional areas of use and emerging areas of application and include; automated SEM techniques, electron backscattered diffraction, charge contrast and in situ SEM imaging, EPMA mapping techniques, the determination of chemical states in minerals and materials using changes in X-ray peak shape, hyperspectral EPMA, and trace-element speciation using quantitative cathodoluminescence.

ABSTRACT The Popigai (100 km in diameter) and the Chesapeake Bay (40–85 km diameter) impact structures formed within ~10–20 k.y. in the late Eocene during a 2 m.y. period with enhanced flux of 3 He-rich interplanetary dust to Earth. Ejecta from the Siberian Popigai impact structure have been found in late Eocene marine sediments at numerous deep-sea drilling sites around the globe and also in a few marine sections outcropped on land, like the Massignano section near Ancona in Italy. In the Massignano section, the Popigai layer is associated with an iridium anomaly, shocked quartz, and abundant clinopyroxene-bearing (cpx) spherules, altered to smectite and flattened to “pancake spherules.” The ejecta are also associated with a significant enrichment of H-chondritic chromite grains (>63 μm), likely representing unmelted fragments of the impactor. The Massignano section also contains abundant terrestrial chrome-spinel grains, making reconstructions of the micrometeorite flux very difficult. We therefore searched for an alternative section that would be more useful for these types of studies. Here, we report the discovery of such a section, and also the first discovery of the Popigai ejecta in another locality in Italy, the Monte Vaccaro section, 90 km west of Ancona. The Monte Vaccaro section biostratigraphy was established based on calcareous nannoplankton, which allowed the identification of a sequence of distinct bioevents showing a good correlation with the Massignano section. In both the Monte Vaccaro and Massignano sections, the Popigai ejecta layer occurs in calcareous nannofossil zone CNE 19. The ejecta layer in the Monte Vaccaro section contains shocked quartz, abundant pancake spherules, and an iridium anomaly of 700 ppt, which is three times higher than the peak Ir measured in the ejecta layer at Massignano. In a 105-kg-size sample from just above the ejecta layer at Monte Vaccaro, we also found an enrichment of H-chondritic chromite grains. Because of its condensed nature and low content of terrestrial spinel grains, the Monte Vaccaro section holds great potential for reconstructions of the micrometeorite flux to Earth during the late Eocene using spinels.

Abstract Scanning electron microscopy (SEM) is one of the most frequently used techniques for near- surface characterization of most solid (and some liquid or liquid-containing) materials with a lateral resolution ranging between 1 nm (for surface-morphology observations) and 1 mm (for certain elemental-composition measurements). It works by scanning a finely focused electron beam over a surface and recording a variety of signals obtained from the electron-beam illuminated volume. Besides observation of the morphology of the surface of materials by recording of secondary electrons, SEM allows the measurement of elemental composition ( e.g. by X-ray spectroscopy) and crystallographic nature (by backscattered electrons) of microscopic volumes beneath the surface. Even information on the chemical bonding (by Auger electrons) and on the electronic state ( e.g. by cathodoluminescence) of microscopically small-volume elements can be obtained. Furthermore, direct observation of crystal lattice defects is possible. Many ofthe observations and measurements can be performed simultaneously, thus referring to the same position on a sample surface. Furthermore, materials may be modified during the measurements, e.g. by heating or mechanical loading, and changes canbeobservedeither in situ or by means of interrupted tests. Particularly powerful techniques for characterization of crystalline materials in SEM are electron backscatter diffraction (EBSD) and EBSD-based orientation microscopy. These techniques allow quantitative characterization of microstructures (i.e.defect arrangements) of bulk crystalline materials down to a lateral resolution of ~50 to 200 nm (depending on material and microscope conditions). The largely automated analysis of electron backscatter diffraction patterns (EBSPs) yields the crystallographic phase, orientation, defect density, and, potentially, elastic stress state ofthe illuminated crystal volume. Crystal orientation mapping (COM) is performed by scanning the electron beam over the sample and recording and analyzing a diffraction pattern from every point of the scan grid. The data obtained can then be plotted, for example, in the form of orientation, misorientation or phase maps of the scanned area. These maps reveal all kinds of morphological data such as grain size, grain shape, spatial distribution of phases and defects and much more. Besides this, the orientation data represent the texture ofthe investigated area. Together with EBSD scanning, further signals can be recorded, e.g. the elemental composition via energy-dispersive X-ray spectroscopy (EDX) or optoelectronic properties via cathodoluminescence (CL). This enhances the strength of the technique even further.

Abstract Radon ( 222 Rn) is a natural radioactive gas that occurs in rocks and soils and can only be detected with special equipment. Radon is a major cause of lung cancer. Therefore, early detection is essential. The British Geological Survey and Public Health England have produced a series of maps showing radon affected areas based on underlying geology and indoor radon measurements, which help to identify radon-affected buildings. Many factors influence how much radon accumulates in buildings. Remedial work can be undertaken to reduce its passage into homes and workplaces and new buildings can be built with radon preventative measures.

Abstract Understanding the behaviour of fluids in hydrothermal systems is a key factor in volcano monitoring. Measuring gas emissions in volcanic areas is strategic for detecting and interpreting precursory signals of variations in volcanic activity. The role of radon as a potential precursor of earthquakes has been extensively debated. However, radon anomalies appear to be better suited to forecast eruptive episodes as we know the loci of volcanic eruptions and we can follow the evolution of volcanic activity. Radon mapping is an effective tool in assessing diffuse and concentrated degassing at the surface. We hereby summarize the in-soil radon emissions collected worldwide and further discuss a collection of data on our key targets. These are closed-conduit and open-conduit volcanoes: Vesuvius (Italy) and La Soufrière (Guadeloupe, Lesser Antilles), Stromboli (Italy) and Villarrica (Chile), respectively. In all the above volcanoes, faults and fracture systems control radon degassing. Automatic and real-time measurements help us to detect major changes in volcanic activity. We present and discuss the radon time series associated with the last effusive eruption at Stromboli. Spectral analyses reveal diurnal and semi-diurnal cycles being probably modulated by atmospheric variations. Multiple linear regression (MLR) analyses have been performed by filtering the radon signals from the effects of local environmental parameters. The residuals do not show particular variations or precursory peaks as the gases have been released from this open-conduit volcano before the onset of the effusive phase (7 August 2014). It is finally emphasized that radon is not the sole precursor, and we should also rely on other geochemical and geophysical parameters. In this perspective, we propose a methodological procedure that can contribute to improving volcano surveillance in an attempt to mitigate volcanic risk.