atw - International Journal for Nuclear Power | 05.2020

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