Forschungszentrum Jülich puts the brakes on fast neutrons at the ESS research facility in southern Sweden
Hannover/Jülich. What do hearts have to do with slowing down free neutrons? The answer to this question can be found in the city of Lund in southern Sweden, where the European Spallation Source (ESS) is currently under construction. With a construction budget of 1.85 billion euros, the ESS ranks among Europe’s biggest research infrastructure projects. Germany’s contribution to the project amounts to around 190 million euros and is being coordinated by the Forschungszentrum Jülich research center.
A high-intensity neutron beam can be generated in one of two ways: through nuclear fission or through spallation. Spallation produces neutron beams with a higher energy density and therefore a higher intensity. More importantly, it produces pulsed beams, which enables precision time-resolved measurements.
A spallation source is comprised of a proton accelerator, the target and a cold moderator. The proton accelerator directs proton beams at the atomic nuclei of the target at near light speed. While the beams dislodge only a few neutrons on impact, they excite the atomic nuclei, thereby expelling, or spalling, from 20 to 30 usable neutrons per nucleus. Since the neutrons spalled in this way are too fast and of too high energy to be used for experimental purposes, they need to be slowed down. But how? The speed of the neutrons emitted by the target needs to be reduced from around 20,000 kilometers per second to under 0.5 kilometers per second.
To meet this challenge, scientists and engineers at Forschungszentrum Jülich have developed a para-hydrogen moderator encased in high-strength aluminum alloy. This pressure vessel, which is also known as the « cold heart », is operated at -250°C (-418°F) and 10 bar of pressure, and emits around 4,000 watts of radiant heat. Despite its small size, it is critically important in that it determines the quality of the neutron beam. Such moderators, which are always used in pairs and in combination with a cooling system, reduce the speed of liberated neutrons before these enter the beam trajectory in any given experiment.
« Neutron research using such a high-power source gives us a unique opportunity to investigate biological processes and new materials, » explained Dr. S. M. Schmidt, a member of the executive board of Forschungszentrum Jülich. « With its decades of expertise, Forschungszentrum Jülich is ideally suited to coordinating Germany’s contributions to what is one of Europe’s biggest research projects and will play a key role in its success. »
Forschungszentrum Jülich will be showcasing its « Swedish project » at the North Rhine-Westphalia group pavilion (B30) in Hall 2 at this year’s HANNOVER MESSE. Sweden is the official Partner Country to be featured at HANNOVER MESSE 2019.