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Online Annual Report 2012

Scientific Highlights

Battery Storage for the Energy Turnaround

FlüssigmetallbatterieThe federal government’s goal is to harness 80 percent of Germany’s energy supply from renewable energies by 2050. At that time, if not earlier, new and inexpensive solutions will be needed to store large quantities of energy – for those times when the sun doesn’t shine or the wind doesn’t blow. In January of this year, there were many cloudy days without any wind; in order to compensate for the loss of power from the currently available solar systems and wind turbines at such times, it would have been necessary to have had a storage capacity which is 142 times that of the Goldisthal reservoir in Thuringia, Germany’s largest hydroelectric power plant, says Dr. Tom Weier from the Institute of Fluid Dynamics. The storage requirement will have to increase even further in the future if the proportion of regenerative energy sources is to be expanded. Tom Weier and his colleagues are working on a battery that stores power with the help of liquid metals. The principle has been known for a long time already; Prof. Donald Sadoway from the Massachusetts Institute of Technology developed the concept further for large stationary storage systems. But there is one problem: The strong current which is created during charging and discharging can damage a large operational battery. Weier and his team have found a patented solution that prevents this from happening.

The design of a liquid metal battery is quite simple: When metals melt at several hundred degrees Celsius, they array themselves in layers due to their different densities and, thus, become functional storage systems. A light and a heavy metal such as, for example, sodium and bismuth serve as electrodes which are separated by a molten salt, e.g. sodium chloride, which acts as an electrolyte. Electromagnetic forces which may put the fluids into motion are, though, also produced when the current flows during charging and discharging. One possible cause for liquid motion is the current driven Tayler instability. If the electrodes should happen to touch each other, then this creates a short circuit and results in battery failure. The researchers contain the electromagnetic forces with a simple design: They lead the current through an additional conductor right through the battery core; this prevents the creation of possible fluid flows. While cooperating with the Leibniz Institute for Astrophysics Potsdam, the researchers also demonstrated for the first time ever in a lab the Tayler instability last year.

At the moment, the scientists are building a small prototype. For later commercial use, liquid metal batteries are to have a volume in the order of cubic meters with inexpensive source materials and easy production. They could, for example, supply 200 households per day with power and, thus, contribute towards balancing the supply and demand in future energy systems.

  • Publications:
    • Martin Seilmayer, Frank Stefani et al.: “Evidence for transient Tayler instability in a liquid metal experiment”, Physical Review Letters 108 (2012), p. 244501 (DOI: 10.1103/PhysRevLett.108.244501)
    • Frank Stefani et al.: “How to circumvent the size limitation of liquid metal batteries due to the Tayler instability”, Energy Conversion and Management 52 (2011), 2982-2986 (DOI: 10.1016/j.enconman.2011.03.003)
  • Contact: Dr. Tom Weier / Institute of Fluid Dynamics

A New Approach for Decontamination Agents

Arbeiten an einer Heißen Zelle im Institut für Radiopharmazeutische Krebsforschung des HZDRCitric acid is not only widespread in the plant kingdom but is also found in all organisms. Because the citrate molecule is a key intermediate product in the metabolism (“citric acid cycle”). Studies at the HZDR’s Biogeochemistry Division were able to demonstrate that citrate also plays an important role in binding radioactive metals. Such metals as curium form stable complexes with citrate in human urine when its pH value is slightly acidic. This observation provides a first approach in developing new, selective, and tolerable decontamination agents in the future.

During a nuclear accident or an incident at a final repository site, radioactive substances escape into the surrounding environment. In order to be able to respond appropriately during such an accident, it is important to know how such radioactive elements react and behave in the environment and the body – when, for example, they are absorbed through the food chain. What compounds do they form? How do they spread? What effects do they have on the metabolism? That is why HZDR researcher Anne Heller and her colleagues took a closer look at the radioactive heavy metal curium as well as the chemically related, but non-radioactive metal europium. The scientists discovered that both elements are bound as trivalent ions with the help of citrate in human urine when its pH value is acidic. The concentrations and pH values were varied and the properties as well as the structures of the created citrate complexes were ascertained during extensive tests. Quantum chemical calculations support the experimental findings which indicate that various stable complexes are created with diverse structures. This might make citrate a good starting point for developing a new detoxicant and decontamination agent in the future that could render trivalent radioactive metals harmless in the body. Conventional substances in use today have several disadvantages: They are based on exogenous substances, have to be applied promptly over a long period of time, and also bind other essential metal ions in the body. In order to pursue this approach further, the HZDR scientists are now investigating how the trivalent metals curium and europium behave in blood and other bodily fluids.

  • Publications:
    • Anne Heller et al., "Curium(III) citrate speciation in biological systems: a europium(III) assisted spectroscopic and quantum chemical study”, Dalton Trans. 41, p. 13969-13983 (2012; DOI: 10.1039/C2DT31480K)
    • Anne Heller et al., "Chemical speciation of trivalent actinides and lanthanides in biological fluids: The dominant in vitro binding form of curium(III) and europium(III) in human urine”, Chem. Res. Toxicol. 24, p. 193-203 (2011; DOI: 10.1021/tx100273g)
  • Contact: Dr. Anne Heller / Institute of Resource Ecology

Perfusion Measurement for Optimized Radiation Therapy

Kombiniertes PET/MRT-Gerät am HZDRThe researchers at the PET Center, which is operated jointly by the HZDR and TU Dresden, are working on an improved characterization of tumors. The scientists headed by Jörg van den Hoff don’t just want to identify tumor tissue in the body and localize it precisely; they also want to ascertain its circulation, the so-called perfusion. A new measurement technology is to provide more information on the possible success of cancer treatments and, thus, assist the planning of individual therapies.

The PET MRI system installed at the HZDR provides very detailed views of the body already today. The unit combines two diagnostic methods: While the PET system identifies tumor tissue due to its higher metabolism, the MRI system provides images of the brain or inner organs with a high spatial resolution and a high contrast. The simultaneous examination creates already images with which doctors can easily identify the position and function of tumor tissues. In the future, the HZDR researchers want to also measure with the device how the tumor tissue is supplied with blood so as to have another important parameter for the medical diagnosis.

They actually take advantage of the fact that it is possible to magnetize the circulating blood with the MRI system and, thus, also mark it. The blood flows through the arteries into the tissue while the magnetization subsides. This reduction can be depicted according to elapsed time and volume. With the help of such measurements, researchers can, for example, ascertain which parts of a tumor are not well circulated, i.e. perfused. The simultaneous recording of the local circulation and metabolism with the PET MRI unit promises to bring a new quality to imaging diagnostics and, thus, also provides improved possibilities to plan and adjust a therapy more precisely.

  • Publication: J. Petr et al., "Partial volume correction in arterial spin labeling using a Look-Locker sequence“, Magnetic Resonance in Medicine (2012; DOI: 10.1002/mrm.24601)
  • Contact: Prof. Jörg van den Hoff / Institute of Radiopharmaceutical Cancer Research

Electrons in Quantum Dots

Der Freie-Elektronen-Laser im HZDR erzeugt quasi einfarbiges Licht im infraroten Bereich, dessen Wellenlänge frei einstellbar ist. (Foto: HZDR/Frank Bierstedt)New or modified materials are very important to many sectors of today’s society. They permit, for example, the faster storage and transmission of information. The properties of those materials on which these effects are based are, though, to a large extent still unknown. Quantum dots are such an example. They are nanostructures in semiconducting materials; and they are a prerequisite for new components in electronics, optoelectronics, or quantum information processing. Scientists still have to find out how precisely electrons, which are responsible for the material properties, behave in these structures. Dr. Stephan Winnerl from the Institute of Ion Beam Physics and Materials Research took an important step in this direction together with his Dresden colleagues.

Quantum dots look like tiny pyramids. Each individual nanopyramid contains only one or two electrons which essentially sense the narrow walls around them and are, thus, impaired considerably in their mobility. Unlike in “normal” solid bodies, electrons assume only a very specific energy level in a nanopyramid. Their location depends not only on the chemical composition of the semiconductor material, but also on the size of the nanopyramids. The team of researchers headed by Stefan Winnerl observed for the first time ever the transitions in the mid-infrared range between the energy levels of individual quantum dots.

The scientists used one of the Free-Electron Lasers at the HZDR and applied infrared light to the nanostructures. The electrons absorb energy during this bombardment and are raised to a higher energy level; backscattered light permits the measurement of the energy transfer. “The clearly defined energy levels in the quantum dots are, for example, used in very energy efficient lasers;” says Stefan Winnerl. “The light is created because an electron falls from a higher energy level to a lower one. The energy difference between both levels determines the color of the light.” Next, the researchers want to examine the behavior of electrons in quantum dots in mid-infrared ranges at lower temperatures in order to gain even more precise insights into the imprisoned life of electrons.

  • Publication: R. Jacob, S. Winnerl et al.: "Intersublevel spectroscopy on single InAs-quantum dots by terahertz near-field microscopy“, in Nano Letters, vol. 12 (2012), p. 4336 (DOI: 10.1021/nl302078w)
  • Contact: Dr. Stephan Winnerl / Institute of Ion Beam Physics and Materials Research