atw - International Journal for Nuclear Power | 05.2020

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atw Vol. 65 (2020) | Issue 5 ı May RESEARCH AND INNOVATION 260 2009 Fusion of HMI and BESSY – establishment of a common user service In January 2009, the Hahn Meitner Institute (HMI) and the Berliner Elektronenspeicherring-Gesellschaft für Synchrotronstrahlung (BESSY) merged to form the Helmholtz Center Berlin (HZB) for materials and energy. The fusion promoted the combined use of photons and neutrons in one location. Numerous research fields benefited from this, including the photovoltaics and materials research established at the HMI. In November 2009, the HZB invited to the “First Joint BER II and BESSY II Users’ Meeting”. More than 350 participants from all over the world accepted the invitation and had a cross-disciplinary exchange. 2010 – 2012 Replacement of the conical beam tube and upgrade of the neutron guide The long-planned replacement of the conical nozzle became necessary because the maximum service life for this component would have been reached in 2011. Other components, such as the cold neutron source with a moderator cell through which the neutrons fly, were also replaced. The scientists also used the break to improve the instruments and replace the neutron guides. They received a super mirror coating, three were widened and an additional (sixth) neutron guide was built. These improvements significantly increased the neutron flux – an enormous improvement for science that kept the BER II internationally competitive. 2013 Shut down decision | Exchange of the conical nozzle. On June 25, 2013, the supervisory board of the HZB decided to end science operations at the research reactor BER II at the end of 2019. With the early announcement of the shutdown date, both the scientific users of BER II and the management were given planning security to set the course for a successful reorientation of research. The first plans for the dismantling of BER II already began in 2014. At the same time, interested parties in other neutron sources were addressed so that the neutron instruments are still available for research after the BER II has been switched off. 2015 Commissioning of the high field magnet After eight years of construction and development, the world’s strongest magnet for materials research with neutrons was put into operation. It operates with a hybrid magnet system and produces magnetic fields up to a strength of 26 Tesla. A normally conductive and a superconducting coil are connected in series. Cooperation partners from several countries were involved in the development of the high field magnet. The high field magnet laboratory in Tallahassee, USA was the lead partner in the partner consortium. Even if the high field magnet at HZB was only in operation for about five years, its construction is considered a pioneering achievement and scientific experiments have shown which questions can be investi gated with such high magnetic fields. 2017 Application for shut down In April 2017, the HZB submitted the basic application for decommis sioning and dismantling of BER II, which initiated the extensive approval process. In order to enable early public participation, the HZB invited to an information event at the end of 2017, attended by over a hundred interested parties. | Commissioning of the high field magnet. The dialogue group that subsequently formed has been working regularly since then and supports the dismantling process. 2018 The last neutron school The last neutron school at BER II took place in February 2018. After 38 successful years, the school has continued at the Australian institution ANSTO – with the participation of the HZB – since 2019. December 11, 2019 End of operation The last time the reactor delivered neutrons was on December 11, 2019. Until then, eighteen neutron instruments were still in operation, ten of which were in full user operation. The measuring time was fully booked up to the last shift: In the last year of operation, there were more than 600 visits by users to BER II. Research and Innovation BER II – The End of an Era ı Helmholtz-Zentrum Berlin für Materialien und Energie
atw Vol. 65 (2020) | Issue 5 ı May Research Highlights SOLID-STATE PHYSICS AND MAGNETISM Magnetic monopoles discovered A sensational discovery was made at HZB in 2009: physicists led by HZB researcher Alan Tennant have demonstrated for the first time that magnetic monopoles can form under very special conditions. The North Pole and South Pole are separated from each other as far as it normally never happens! The exotic observation was achieved at temperatures almost at absolute zero in a dysprosium titanite crystal. With the help of neutron scattering, the HZB researchers were able to show that the magnetic moments inside the crystal are arranged in so-called spin spaghetti, at the ends of which the north and south poles are located. And because these are so far apart, the spin spaghetti behave like mono polies. The existence of such magnetic monopoles is predicted by quantum physics, but has never been observed before. The golden cut exists also in the quantum world At BER II, scientists have dis covered previously unknown symmetry properties in solid matter. The “golden ratio” is known from art and architecture. The researchers have now found its characteristics in the atomic structure of a crystal made of cobalt niobate. Exotic material state: “Liquid” quantum spins A team at the HZB has experimentally detected a so-called quantum spin liquid in a single crystal made of calcium chromium oxide. It is a new kind of state of matter. The huge advantage about the dis covery: According to popular beliefs, the quantum phenomenon should not have occurred in this material. The work extends the understanding of condensed matter and could also be important for the future development of quantum computers. A new condition of water: Like ice, but moveable Water is liquid at room temperature. But enclosed in the tiny channels of a zeolite structure, the water flows much tougher. A new state of matter of water in zeolite has now been discovered on the time-of-flight spectrometer NEAT at the neutron source BER II: in the nanochannels of the zeolite structure, the water molecules arrange themselves like in the ice crystal, but still remain as mobile as in a liquid. The inclusion in nanochannels enhances cooperative inter actions between water molecules. The results are important for the design of zeolite storage tanks, which are used as energy-saving air conditioning units for cooling. 3-D imaging – first insight in magnetic fields 3-D images are not only generated in medicine, for example with the help of X-ray or magnetic resonance imaging. Materials scientists also like to look inside a body. A team at the HMI has now succeeded for the first time in threedimensional representation of magnetic fields inside massive, non-transparent materials using polarized neutrons at the neutron source BER II. FACTS & FIGURES p Year of construction: 1972, reopening after renovation and approval: 1991 p Termination of the operation: December 2019 (decision of the HZB supervisory board) p Type: open, light water moderated swimming pool reactor p Pool measurements: 200 m 3 water capacity, two pools each 3.5 m in diameter and 11 m deep linked by a channel 2 m wide p Delivery: p 10 MW of thermal power p about 2 x 10 14 neutrons per square centimetre and second in the core p Fuel elements: 24 standard elements each with 322 g of U-235 and 6 elements for receiving the control rods each with 238 g of U-235 p Control rods: 6 neutron absorbers p Reflector: 32 cm beryllium jacket ENERGY RESEARCH Transport processes in fuel cells How liquid water is distributed inside a fuel cell is crucial for its efficiency and service life. With neutron tomography at BER II, fuel cells can be analyzed in operando, i.e. while hydrogen and oxygen react to water. The scientists were also able to investigate the influence of membranes and different electrodes. Kesterite solar cells Kesterites are semiconductor compounds made up of several abundant elements. They can be used in solar cells to convert light into electrical energy. A team at the HZB produced kesterite samples and varied the composition. With neutron diffraction at BER II, they were able to determine how the different material com position affects defects and thus the efficiency of the solar cells. Further research showed that Germanium can improve the optoelectronic properties of the material. Batteries with silicon anodes In theory, silicon anodes could store ten times more lithium ions than the graphite anodes that have been used in commercial lithium batteries for many years. In practice, however, the capacity of silicon anodes drops sharply with every further charge-discharge cycle. A HZB team used neutron experiments at BER II and the Institut Laue-Langevin in Grenoble to clarify what happens on the surface of the silicon anode during charging and which processes reduce capacity: when charging, a blocking build-up occurs on the silicon surface layer that prevents the penetration of lithium ions. Now developers can specifically look for ways to break down or prevent this layer. HEALTH & LIFE RESEARCH AND INNOVATION 261 ART & CULTURE Painting research: “Young Woman with a Dish of Fruit” The “Young Woman with a Dish of Fruit” was painted by Titian in Venice in the 16th century. The picture at BER II was examined with neutrons on behalf of the Gemäldegalerie. The neutrons stimulate the colour pigments so that the type of pigments can be inferred from them. The investigation revealed a surprise: Titian had already used Naples yellow for the girl’s gold- embroidered dress in 1555. This colour is only mentioned in the literature from 1702! It shows how far the powerful commercial power of Venice was internationally networked. (2001) Surprising finding in the snout of a fossil Scientists from the Natural History Museum Berlin have examined a petrified Lystrosaurus skull with neutron tomography at the HZB. This enabled them to create a three-dimensional image layer by layer, in which harder and softer components in the skull could be distinguished from one another. In the area of the snout they found traces of soft cartilage tissue, which indicate the existence of sinuses. A surprise, because the Lystrosaurus was already on the way to becoming a warm-blooded animal. How toxic proteins intend in nervous cells “Senile plaques” are found as typical deposits in the brains of deceased Alzheimer’s patients. However, these are probably not the cause, but rather the result of Alzheimer’s disease. Perhaps the plaques even serve as protection because they bind harmful proteins that would otherwise float freely. Smaller aggregates of the protein β-amyloid could be toxic. At BER II, a team with neutron diffraction investigated how β- amyloid can penetrate the membrane of nerve cells. The results made it possible to determine the position and mo bility of the toxic protein and confirmed the assumption that β-amyloid can penetrate nerve cells. Compatible joint prostheses In joints, the bones are equipped with cartilage and a layer of lipid membranes and move against each other in a liquid-filled capsule. This joint lubrication ensures painless mobility. At the neutron source BER II, researchers have investi gated this situation in a model system with synthetic lipid membranes and synthetic joint lubrication. They were able to measure how the distances between the individual lipid membranes of the “bone” coating increase with increasing temperature and how the surface of the artificial joint behaves under different pressure and shear forces. The results are interesting for the development of compatible joint prostheses. Research and Innovation BER II – The End of an Era ı Helmholtz-Zentrum Berlin für Materialien und Energie
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atw - International Journal for Nuclear Power | 05.2020

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