Scientists at Johannes Gutenberg University Mainz (JGU) in Germany have built what is currently the strongest source of ultracold neutrons. Ultracold neutrons (UCNs) were first generated here five years ago.
View of TRIGA Mainz and its UCN sources at beam tube C and D. photo: Thorsten Lauer / Yuri Sobolev
They are much slower than thermal neutrons and are characterized by the fact that they can be stored in special containers. This property makes them important tools for experiments to investigate why matter dominates over antimatter in our universe and how the lightest elements were created directly after the Big Bang.
"We have commissioned a new UCN source and improved the overall procedure so that we can now generate and store considerably more ultracold neutrons than before and more than anybody else," says Professor Werner Heil of the Institute of Physics at Mainz University. Having so far managed to achieve a density of ten UCN per cubic centimeter, the Mainz research team of chemists and physicists has become one of the global leaders in this research field.
In 2006, the Mainz team, working in cooperation with the Technical University of Munich, produced for the first time ultracold neutrons using the pulsed Mainz TRIGA reactor. Neutrons are created by means of nuclear fission in the TRIGA research reactor in Mainz. These fission neutrons reach speeds up to 30,000 kilometers per second – a tenth of the speed of light. Interaction with light atomic nuclei in the reactor slows them down to a 'thermal' speed of approximately 2,200 meters per second. The apparatus developed by the researchers from Mainz University is then employed: a three meter long tube is inserted in the beam tube of the reactor at the point where there is the highest flux of thermal neutrons. The thermal neutrons undergo extreme velocity deceleration in this tube.
This new source of UCNs in beam tube D of the Mainz TRIGA reactor has just successfully completed its first stress test. In the UCN apparatus the thermal neutrons are slowed down in two in two steps: first with hydrogen and thereafter with an ice block made of deuterium at minus 270 degrees Celsius. "The neutrons are now so slow that we could run after them," says Professor Werner Heil. The UCNs move to the experimental site at the other end of the tube at a speed of only 5 meters per second. The stainless steel tube is coated inside with nickel to ensure that no neutrons are lost on the way.
The key parameter for the scientists is the UCN density that can be achieved at the site of the experiment – a prerequisite to perform high-precision experiments. "In our first trial, we achieved ten UCN per cubic centimeter in a typical storage volume of ten liters. When we use hydrogen as a pre-moderator and make a few minor changes, we expect fifty UCN per cubic centimeter," explain Dr Thorsten Lauer and Dr Yuri Sobolev, who supervise the system. This is more than sufficient to perform experiments such as measurements to determine the life time of the neutron. With this UCN density, the Mainz research team is now the front-runner in the race to achieve the highest storage density, in which facilities in Los Alamos, Grenoble, Munich and the Swiss city of Villigen are competing.
The life time of a neutron – according to current scientific findings – is approximately 885 seconds, but this number is dominated by systematic errors. The method employed is known as "counting the survivors": the number of neutrons left after a certain decay time is correlated with the known initial number in the sample. Till now, for more precise life time measurements not enough ultracold neutrons were available.
UCN research at Johannes Gutenberg University Mainz is part of the "Precision Physics, Fundamental Interactions and Structure of Matter" (PRISMA) Cluster of Excellence, which is currently applying for additional funding in Germany’s Federal Excellence Initiative. The new UCN source was constructed directly on the university campus by the workshops of the Institutes of Physics and Nuclear Chemistry. Over the last three years, seventeen undergraduates, two doctoral candidates and two post-doctoral students have worked on the UCN project – a field that will provide a great deal of scientific insight in the future.Publications:
I. Altarev, F. Atchison, M. Daum, A. Frei, E. Gutsmiedl, G. Hampel, F.J. Hartmann, W. Heil, A. Knecht, J.V. Kratz, T. Lauer, M. Meier, S. Paul, Y. Sobolev, N. Wiehl: Neutron velocity distribution from a superthermal solid 2H2 ultracold neutron source. Eur. Phys. J. A 37 (2008) 9.
Petra Giegerich | idw
New quantum liquid crystals may play role in future of computers
21.04.2017 | California Institute of Technology
Light rays from a supernova bent by the curvature of space-time around a galaxy
21.04.2017 | Stockholm University
The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.
Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...
The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...
Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.
Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...
Two researchers at Heidelberg University have developed a model system that enables a better understanding of the processes in a quantum-physical experiment...
Glaciers might seem rather inhospitable environments. However, they are home to a diverse and vibrant microbial community. It’s becoming increasingly clear that they play a bigger role in the carbon cycle than previously thought.
A new study, now published in the journal Nature Geoscience, shows how microbial communities in melting glaciers contribute to the Earth’s carbon cycle, a...
20.04.2017 | Event News
18.04.2017 | Event News
03.04.2017 | Event News
21.04.2017 | Physics and Astronomy
21.04.2017 | Health and Medicine
21.04.2017 | Physics and Astronomy