Prof. Dr. Cornelius Fischer

Head of Department
Reactive Transport
Phone: +49 351 260 4660

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Equipment of the Department of Reactive Transport

Foto: PET-Labor in der Forschungsstelle Leipzig ©Copyright: André Künzelmann

PET Lab at the facility Leipzig

Positron Emission Tomography (PET)

We have adopted positron emission tomography (PET) for the purpose of flow field tomography in opaque materials, particularly geomaterials. PET is characterized by its unmatched sensitivity and selectivity for positron-emitting radiotracers. We apply a ClearPET scanner (Elysia-Raytest) to (geo)material samples and benefit from its miniaturization compared to clinical PET scanners: its small gantry diameter (adjustable to 13 or 21 cm) and the small size of the detector crystals allow to reach the physical spatial resolution limit of about 1 mm on standard drill cores (in contrast to the physical resolution limit of medical PET scanners of 3-5 mm). PET has a sensitivity to tracer concentrations of about 107 tracer atoms/µl, assuming an activity detection limit of 1 kBq/mm3 or better, which is several orders of magnitude better than other imaging modalities. PET is ideally suited for direct observation of flow and transport processes in geomaterials.

A unique feature of our scanner is a proprietary tilting device that allows the gantry axis to be tilted from the standard horizontal to the vertical orientation, which is the common sample orientation in geoscience transport experiments.

In a typical analysis, the PET tracer (a substance labeled with a positron-emitting radionuclide) is injected into the sample, similar to conventional column experiments. The photon radiation emitted by the tracer is detected. The current spatial distribution of the tracer concentration is then calculated from the detection positions as a sequence of frames with frame lengths ranging from minutes to hours. The duration of the experiment depends on the decay time of the tracer (e.g. 18F: 109.77 min, 22Na: 2.6018 a). PET tracers are supplied by our in-house cyclotron.

PET images the concentration of the tracer, a key parameter of geochemical transport, with molecular sensitivity and millimeter-scale resolution. Compared to conventional column experiments, PET provides much more detailed insight into transport processes and comprehensive parameter sets such as velocity distribution, distribution of effective pore volume, an estimate of the effective internal surface area, and often reveals preferential transport pathways. In contrast, µCT provides microscale images of the internal structure with micrometer resolution.

We have optimized the reconstruction process for measurements on geological materials, taking into account the high density and thus strong attenuation and scattering effects, and taking advantage of the open software environment of the scanner.

µ-focus X-ray CT-scanner (µCT)

We use a Nikon XT H 225 µ-focus X-ray CT scanner (µCT) to analyze the internal structures of various (geo)materials and to derive mass attenuation phantoms for PET raw data corrections of dense materials. The CT scanner is equipped with a µ-focus reflection X-ray source with a minimum focal spot of 1 µm, a maximum energy of 225 keV and a maximum power of 225 W. The detector is a 2000×2000 16-bit flat panel detector with a size of 400×400 mm2 (Varian 4030). The sample is positioned by a 5-axis manipulator capable of handling a maximum load of 15 kg. The radiation protection cabinet has an internal size of 990×500×890 mm3, allowing the placement of auxiliary experimental units outside the field of view. The manipulator has a working range of 185×280×730 mm3.

The image resolution depends on the imaging geometry, i.e. the distance from source to object and from object to detector. Full-size drill cores with a diameter of 100 mm are imaged with a voxel size of about 70 µm, while high magnifications with voxel sizes of 2-5 µm are possible on mm-sized objects.

Image reconstruction is performed using the Nikon OEM software CTPro3D. For further image processing and presentation, the commercial software package Avizo (ThermoFisher Scientific) or open source packages such as ParaView or the Python package MayaVi are used.

The large amount of data requires a high performance computing workstation for image processing (e.g. memory > 200 GB, graphics processor with ≥ 8 GB).

Foto: SENSOFAR Interferometric/Confocal Microscope ©Copyright: PD Dr. Cornelius Fischer

The surface landscape of the PET bottle on your desk, recorded by phase-shifting interferometry. (The small bumps are molecular in z-direction.)

Vertical Scanning Interferometry & Confocal Microscopy

This instrument is designed to map surface topographies with a wide range of roughness by combining three optical techniques: Vertical Scanning Interferometry, Confocal Profiling and Focus Detection. The only prerequisite for the sample is sufficient reflectivity. Light intensities are recorded in a piezo-driven height scan, laterally resolved by a CCD cam. The z-positions of a distance criterion (equal interferometric path lengths or optical focus) are recorded for each pixel (x, y position), resulting in the surface image.

Scanning Electron Microscope (SEM)

The Jeol JSM IT200 SEM with continuously adjustable acceleration voltages allows analysis of both cathodoluminescence and backscatter imaging as well as spatially resolved elemental analysis by EDS. The Jeol JSM IT200 SEM is typically used to analyze thin sections of material samples for mineralogical/elemental composition, grain size, pore space and surface structure, or to characterize (nano-)particle samples. In general, a conductive surface coating (e.g. Au/Pd) is required for the measurement. A sputter coater (Quorum Q150TS) is available for this purpose.

Foto: Storage Phosphor Screens ©Copyright: PD Dr. Cornelius Fischer

Storage Phosphor Screens

Storage Phosphor Screens

Phosphor storage screens are used to collect a 2D spatially resolved image of radionuclide distributions in/on samples. The screens are exposed to the radiation source and an image of the source distribution is stored in the radiation sensitive layer of the screen. The image can then be read using an Amersham Typhoon biomolecular imager provided by our colleagues at the Institute of Radiopharmaceutical Cancer Research. In our group, the analytical technique is typically used to image the distribution of sorbed radionuclides on mineral samples.

Foto: Liquid Scintillation Counting (LSC) ©Copyright: PD Dr. Cornelius Fischer

Liquid Scintillation Counting (LSC)

Liquid Scintillation Counting

The liquid scintillation analyzer Tri-Carb 3110 TR (Perkin Elmer) is a multi-channel analyzer with 0.1 keV resolution. It utilizes two photomultiplier tubes in coincidence mode. A quench correction with 133Ba as external standard is applied.

This instrument is mainly used for the detection of 3H and 14C, but is also applicable to gamma emitters. A special application in our department is the analysis of tritium in gaseous isotope mixtures after catalytic conversion to HTO (900°C, CuO). Furthermore, HTO is an ideal non-reactive tracer in column experiments. We use the LSC for the analysis of 14C-labeled organic compounds and for the routine control of laboratory waste water. We are currently investigating the possibility of miniaturizing this device in microfluidic setups.

Foto: Gamma-Ray Spectrometry ©Copyright: PD Dr. Cornelius Fischer

Gamma-Ray Spectrometry

Gamma-Ray Spectrometry

High purity germanium (HPGe) radiation detectors are used with modular and integrated electronic systems for gamma-ray spectrometry. Different detector configurations allow for the adaptation to a wide range of required measurement geometries, gamma-ray energies and count rates.


Foto: Gamma-Ray Spectrometry Hardware ©Copyright: Gamma-Ray Spectrometry Hardware

Foto: Zetasizer ©Copyright: PD Dr. Cornelius Fischer



The Malvern Zetasizer Nano is a dynamic light scattering instrument capable of measuring the hydrodynamic diameter of colloids as well as their surface charge (zeta potential). The hydrodynamic diameter of colloidal dispersions is measured by dynamic light scattering. Changes in particle size due to aggregation, adsorption, particle growth, dissolution can be monitored. In addition, the ability to perform electrophoretic light scattering experiments allows the measurement of particle zeta potential as a measure of colloidal stability. The instrument is equipped with a titration add-on that allows automated measurement of pH series or concentration series of additives.