X ray Compton Tomography

The potentials of incoherent X ray scattering Compton tomography are investigated. Imaging materials of very different density or atomic number at once is a perpetual challenge for X ray tomography or radiography, in general. In a basic laboratory set up for simultaneous perpendicular Compton scattering and direct beam attenuation tomographic scans are conducted by single channel photon counting. This results in asymmetric distortions of the projection profiles of the scattering CT data set. In a first approach corrections of Compton scattering data by taking advantage of rotational symmetry yield tomograms without major geometric artefacts. A cylindrical sample composed of PE, PA, PVC, glass and wood demonstrates similar Compton contrast for all the substances, while the conventional absorption tomogram only reveals the two high order materials. Comparison to neutron tomography reveals astonishing similarities except for the glass component without hydrogen . Therefore, Compton CT bears the potential to replace neutron tomography, which requires much more efforts

Capturing 3D Water Flow in Rooted Soil by Ultra fast Neutron Tomography

AbstractWater infiltration in soil is not only affected by the inherent heterogeneities of soil, but even more by the interaction with plant roots and their water uptake. Neutron tomography is a unique non-invasive 3D tool to visualize plant root systems together with the soil water distribution in situ. So far, acquisition times in the range of hours have been the major limitation for imaging 3D water dynamics. Implementing an alternative acquisition procedure we boosted the speed of acquisition capturing an entire tomogram within 10 s. This allows, for the first time, tracking of a water front ascending in a rooted soil column upon infiltration of deuterated water time-resolved in 3D. Image quality and resolution could be sustained to a level allowing for capturing the root system in high detail. Good signal-to-noise ratio and contrast were the key to visualize dynamic changes in water content and to localize the root uptake. We demonstrated the ability of ultra-fast tomography to quantitatively image quick changes of water content in the rhizosphere and outlined the value of such imaging data for 3D water uptake modelling. The presented method paves the way for time-resolved studies of various 3D flow and transport phenomena in porous systems.</jats:p

Neutron computed laminography yields 3D root system architecture and complements investigations of spatiotemporal rhizosphere patterns

Purpose Root growth, respiration, water uptake as well as root exudation induce biogeochemical patterns in the rhizosphere that can change dynamically over time. Our aim is to develop a method that provides complementary information on 3D root system architecture and biogeochemical gradients around the roots needed for the quantitative description of rhizosphere processes. Methods We captured for the first time the root system architecture of maize plants grown in rectangular rhizotrons in 3D using neutron computed laminography NCL . Simultaneously, we measured pH and oxygen concentration using fluorescent optodes and the 2D soil water distribution by means of neutron radiography. We co registered the 3D laminography data with the 2D oxygen and pH maps to analyze the sensor signal as a function of the distance between the roots and the optode. Results The 3D root system architecture was successfully segmented from the laminographic data. We found that exudation of roots in up to 2 mm distance to the pH optode induced patterns of local idification or alkalization. Over time, oxygen gradients in the rhizosphere emerged for roots up to a distance of 7.5 mm. Conclusion Neutron computed laminography allows for a three dimensional investigation of root systems grown in laterally extended rhizotrons as the ones designed for 2D optode imaging studies. The 3D information on root position within the rhizotrons derived by NCL explained measured 2D oxygen and pH distribution. The presented new combination of 3D and 2D imaging methods facilitates systematical investigations of a wide range of dynamic processes in the rhizospher

Three-Dimensional Imaging of Magnetic Domains with Neutron Grating Interferometry

This paper gives a brief overview on3D imaging of magnetic domains with shearing grating neutron tomography. We investigated the three-dimensional distribution of magnetic domain walls in the bulk of a wedge-shaped FeSi single crystal. The width of the magnetic domains wasanalyzed at different locations within the crystal. Magnetic domains close to the tip of the wedge are much smaller than in the bulk. Furthermore, the three-dimensional shape of individual domains wasinvestigated. We discuss prospects and limitations of the applied measurement technique

Three dimensional in vivo analysis of water uptake and translocation in maize roots by fast neutron tomography

Root water uptake is an essential process for terrestrial plants that strongly affects the spatiotemporal distribution of water in vegetated soil. Fast neutron tomography is a recently established non invasive imaging technique capable to capture the 3D architecture of root systems in situ and even allows for tracking of three dimensional water flow in soil and roots. We present an in vivo analysis of local water uptake and transport by roots of soil grown maize plants for the first time measured in a three dimensional time resolved manner. Using deuterated water as tracer in infiltration experiments, we visualized soil imbibition, local root uptake, and tracked the transport of deuterated water throughout the fibrous root system for a day and night situation. This revealed significant differences in water transport between different root types. The primary root was the preferred water transport path in the 13 days old plants while seminal roots of comparable size and length contributed little to plant water supply. The results underline the unique potential of fast neutron tomography to provide time resolved 3D in vivo information on the water uptake and transport dynamics of plant root systems, thus contributing to a better understanding of the complex interactions of plant, soil and wate

Neutron imaging of cadmium sorption and transport in porous rocks

Understanding fluid flow in rocks is crucial to quantify many natural processes such as ground water flow and naturally triggered seismicity, as well as engineering questions such as displacement of contaminants, the eligibility of subsurface waste storage, geothermal energy usage, oil and gas recovery and artificially induced seismicity. Two key parameters that control the variability of fluid flow and the movement of dissolved chemical species are (i) the local hydraulic conductivity, and (ii) the local sorption properties of the dissolved chemical species by the solid matrix. These parameters can be constrained through tomography imaging of rock samples subjected to fluid injection under constrained flow rate and pressure. The neutron imaging technique is ideal to explore fluid localization in porous materials due to the high but variable sensitivity of neutrons to the different hydrogen isotopes. However, until recently, this technique was underused in geology because of its large acquisition time. With the improved acquisition times of newly set-up neutron beamlines, it has become easier to study fluid flow. In the current set of experiments, we demonstrate the feasibility of in-situ 2D and 3D time-lapse neutron imaging of fluid and pollutant percolation in rocks, in particular that of cadmium salt. Cadmium is a hazardous compound that is found in many electronic devices, including batteries and is a common contaminant in soil and groundwater. It also exhibits higher contrast in neutron attenuation with respect to heavy water, and is therefore an ideal tracer. Time-lapse 2D radiographies and 3D neutron tomographies of the samples were acquired on two neutron beamlines (ILL, France and SINQ, Switzerland). We performed two sets of experiments, imbibition and injection experiments, where we imaged in-situ flow properties, such as local permeability and interactions between cadmium and the solid rock matrix. Our results indicate that even within these cm-scale porous rocks, cadmium transport follows preferential pathways, and locally interacts within the limestone samples. Our results demonstrate that the use of neutron imaging provides additional insights on subsurface transport of pollutants.Applied Geophysics and Petrophysic

Wheat root system architecture and soil moisture distribution in an aggregated soil using neutron computed tomography

Non-invasive techniques are essential to deepen our understanding of root-soil interactions in situ. Neutron computed tomography (NCT) is an example of such techniques that have been successfully used to study these interactions in high resolution. Many of the studies using NCT however, have invariably focused on lupine plants and thus there is limited information available on other more commercially important staple crop plants such as wheat and rice. Also considering the high neutron sensitivity to hydrogen (e.g. water in roots or soil organic matter), nearly all previous in-situ NCT studies have used a relatively homogeneous porous media such as sand, low in soil organic matter and free from soil aggregates, to obtain high-quality images. However to expand the scope of the use of NCT to other more commercially important crops and in less homogenous soils, in this study we focused on wheat root growth in a soil that contained a considerable amount of soil organic matter (SOM) and different sized aggregates. As such, the main aims of this research were (1) to unravel wheat (Triticum aestivum cv. Fielder) root system architecture (RSA) when grown in an aggregated sandy loam soil (<4 mm) with 4% SOM content, (2) Map in 3D, soil water distribution after a brief drying period and (3) to understand how the root system interacts with soil moisture distribution brought about by soil structural heterogeneity. To achieve these, wheat seedlings were grown for 13-days in aluminium tubes (100 mm height and 18 mm diameter) packed with soil and imaged for the first time at the IMAT neutron beamline (in the Rutherford Appleton Laboratory, UK). To the best of our knowledge, this is also the first study to use NCT to study wheat root architectural development. Our study proved that NCT can successfully be used to reveal wheat RSA in a heterogeneous aggregated soils with moderate amounts of SOM. Lateral root growth within the soil column was increased in regions with increased finer soil separates. NCT was also able to successfully map water distribution in a 3D and we show that large macro-aggregates preferentially retained relatively higher soil moisture in comparison to the smaller soil separates within our samples (Fig. 1). This highlights the importance large macro-aggregates in sustainable soil management as they may be able to provide plants water during periodic dry spells. More in situ investigations are required to further understand the impact of different aggregate sizes on RSA and water uptake

Studies on the tensile state of water in trees

Symbolverzeichnis X 1 Einleitung 1 1.1 Wasser - Physikochemische Grundlagen 3 1.1.1 Die Struktur des Wassers 5 1.1.2 Tensiles Wasser 7 1.2 Wassertransport - Pflanzenphysiologische Grundlagen 10 1.2.1 Die Kohäsionstheorie 10 1.2.2 Die hydraulische Architektur der Bäume 12 1.2.3 Die Wurzel 13 1.2.4 Das Leitgewebe 15 1.2.5 Das Blatt 20 Grundlagenuntersuchungen zur Struktur des tensilen Wassers 2 Infrarotspektroskopische Studie zum Nachweis tensiler Spannung in wassergefüllten Nanoporen 24 2.1 Motivation 24 2.2 Experimenteller Teil 25 2.2.1 Probenpräparation 25 2.2.2 Die Messmethode 26 2.2.3 Die Schwingungseigenschaften von Wasser 28 2.2.4 Die Hauptbanden im IR-Spektrum 30 2.2.5 Das verwendet Strukturmodell für Wasser 32 2.2.6 Verdunstung aus der TiO2-Modellstruktur 34 2.2.7 Referenzmessung am unbeschichteten Kristall 34 2.2.8 Wasserverdunstung aus unbedeckter TiO2-Schicht 36 2.2.9 Modifizierter Verdunstungsversuch 38 2.3 Zusammenfassung und Schlussfolgerungen 44 Biologische Studien zum Wassertransport 3 Studie zur Lichtabhängigkeit des Saftaufstiegs 50 3.1 Motivation und Aufgabenstellung 50 3.2 Beschreibung des Versuchsaufbaus 54 3.2.1 Beleuchtung 55 3.3 Experimentelle Methoden 56 3.3.1 Bodenfeuchte 58 3.3.2 Lufttemperatur und relative Luftfeuchte 58 3.3.3 Solare Strahlungsintensität 58 3.3.4 Messungen auf Blattebene 59 3.4 Ergebnisse 60 3.4.1 Wassertransport bei Tageslicht 67 3.4.2 Wassertransport bei nächtlicher Beleuchtung 83 3.5 Schlussfolgerungen 96 4 Elektrochemische Potenzialmessungen an einer Linde 101 4.1 Einleitung 101 4.1.1 Experimentelle Methode 102 4.1.2 Ergebnisse und Diskussion 103 4.1.3 Schlussfolgerungen 110 Physikalisch- Chemische Studien zum Wassertransport 5 Demonstration des Transpirationssogs in einer Modellapparatur 114 5.1 Einleitung 114 5.2 Versuchsaufbau 115 5.3 Versuchsdurchführung 123 5.4 Ergebnisse und Schlussfolgerungen 125 6 Thermogravimetrische Untersuchung der Wasserverdunstung unter Infrarotbestrahlung 129 6.1 Motivation und Aufgabenstellung 129 6.2 Experimentelle Methode 133 6.3 Ergebnisse 135 6.3.1 Stimulation der Verdunstung mit IR-Licht 135 6.3.2 Steigerung der Verdunstungsrate bei feuchter Luft 146 6.4 Schlussfolgerungen 151 7 Zusammenfassung 152 8 Literaturverzeichnis 156 DanksagungDie Natur hat einen solargetriebenen Pumpmechanismus für Wasser entwickelt, der die Evolution hochwüchsiger Landpflanzen ermöglichte. Die Verdunstung aus nanoporösen Zellstrukturen erzeugt einen Transpirationssog, der für den Wasseraufstieg in den Pflanzen sorgt. Beim Transport gerät das Wasser in den Leitbahnen (Xylem) unter Zugspannung und geht dabei in einen gedehnten (tensilen) Zustand über. Bäume mit Wuchshöhen über 10m können ihre Wasserversorgung nur bewerkstelligen, weil sie den thermodynamisch metastabilen, tensilen Zustand des Wassers sicher beherrschen. Noch immer ist nicht vollständig geklärt, wie die Pflanzen dem Problem der Kavitation entgegenwirken, sodass ein langfristig stabiler Transport tensilen Wassers gewährleistet ist. In dieser Arbeit, die Grundlagenuntersuchungen mit angewandten biologischen Experimenten verknüpft, werden Erklärungsansätze auf Basis der irreversiblen Thermodynamik präsentiert, die zum detaillierten Verständnis der tensilen Wasserstrategie der Bäume beitragen. In einer spektroskopischen Studie wurde beim Übergang von Wasser in den tensilen Zustand die Ausbildung zusätzlicher Wasserstoffbrückenbindungen beobachtet, die den kohäsiven Zusammenhalt der Flüssigkeit fördert. Die Zunahme stark vernetzter Wassermoleküle folgte dabei einer sigmoidalen Wachstumsfunktion, die kennzeichnend für das kinetisches Verhalten selbstorganisierter (autokatalytischer) Reaktionen ist. Die beobachteten Strukturänderungen lassen sich mit dem Phasenwechsel von Wasser zu Eis vergleichen. In biologischen Experimenten wurde das Transportverhalten einer Linde unter Anwendung nächtlicher Beleuchtung untersucht. Die nichtlineare Abhängigkeit der Saftflüsse von der treibenden Kraft zeigt, dass der Wassertransport ein Phänomen der irreversiblen Thermodynamik darstellt, welches stark durch Selbstorganisationsmechanismen geprägt ist. Trotz vergleichbarer lokaler Beleuchtungsverhältnisse wurden unterschiedliche Saftflussraten am Tag und in der Nacht beobachtet. Dies wurde als Ausdruck alternativer thermodynamischer Systemzustände gedeutet, die beim Auftreten von Selbstorganisation möglich werden. Elektrochemische Messungen in unterschiedlichen Stammhöhen ergaben saftflusskorrelierte Potenzialunterschiede im Xylem einer Linde, welche durch den Sauerstofftransport im Xylemsaft plausibel erklärt werden können. Weiterhin wurde ein Modell zur Demonstration des Wasseraufstiegs realisiert und in thermogravimetrischen Versuchen die Verdunstungsmechanismen der Blätter untersucht. Die vorliegende Arbeit zeigt, dass die Anwendung von Konzepten der irreversiblen Thermodynamik zum detaillierten Verständnis der tensilen Wasserstrategie der Bäume beiträgt.Nature has developed a solar-driven pumping mechanism for water allowing for the evolution of very tall trees. The evaporation from nanoporous cell structures generates suction through transpiration which provides for the water’s ascent in plants. During transport, negative pressure develops within the conducting tissue (xylem) whereby the water is stretched into a new, tensile state. Trees with heights above 10 m can only secure their water supply because they can cope with the thermodynamic, metastable, tensile state of the water. It still has not been fully clarified how plants counteract the problem of cavitation so that a long-term stable transport of tensil water can be guaranteed. In this work, in which basic research is linked to applied biological experiments, the explanatory attempts are presented on the basis of irreversible thermodynamics, which contribute to the detailed understanding of tensile water strategies in trees. In a spectroscopic study the formation of additional hydrogen bonds could be observed at the point of transition of water into the tensile state enhancing the cohesion of the liquid. The increase of strongly cross-linked water molecules thereby followed a sigmoid growth function, which is characteristic for the kinetic behaviour of self- organized (autocatalytic) reactions. The observed structural changes can be compared with the phase transition of water into ice. In biological experiments the water transport of a lime tree was investigated under nocturnal illumination. The non-linear dependency of the sap flow from the driving force shows that the water transport displays a phenomenon of irreversible thermo¬dynamics, which is strongly affected by self-organising mechanisms. Despite comparable local illumination, different sap flow-rates were observed during the day and at night. This was interpreted as states of an alternative thermodynamic system, which were enabled by the presence of the self-organisation. Electrochemical measurements in various heights of the trunk revealed sap flow-correlated potential differences in the xylem of the lime tree, which can be explained through the oxygen transport in the xylem sap. Furthermore, a model to demonstrate the sap ascent was implemented and the evaporation mechanisms in leaves were investigated in thermogravimetric experiments. The present work shows that the application of concepts of irreversible thermodynamics adds to the detailed understanding of tensile water strategies in trees