Compact Moderator-Reflector Assembly for Very Cold Neutrons

Topic  39
Main supervisor U.Ruecker (
MLZ institution FZJ
Local supervisor 1 Harald Haese
Institution S-DH GmbH
Local supervisor 2 Luca Zanini
Institution European Spallation Source
Local supervisor 3
Local supervisor 4
Title UV-visible Microspectroscopy at the instrument BIODIFF
Description The moderation of neutrons is required to achieve the spectrum demanded by the individual instruments depending on the investigations to be performed. In the case of compact neutron sources, reasonable moderator concepts for thermal or cold neutrons, i.e. for the neutron energy range between 2 meV and 500 meV, exist.
Some high-resolution instruments, as e.g. Neutron Spin-Echo or high-resolution SANS require the usage of neutrons with even lower energy, which corresponds to wavelengths above 10 Å. Neutrons in this energy range are denoted as “Very Cold Neutrons” (VCN). Typically, a VCN neutron spectrum cannot be produced as a result of moderation of neutrons with a moderator in thermal equilibrium because the temperature would need to be below 10 K and the heat removal from the moderator and the interaction between neutrons and moderator are not very efficient then. Instead, the low-energy tail of a cold neutron spectrum needs to be boosted with an intelligent moderator-reflector design to transport as many VCN as possible to the sample position of the instrument.
For an optimal setup of a VCN beamline at a compact accelerator-driven neutron source, suitable moderator-reflector assemblies need to be designed and simulated. In the framework of the HighNESS project at the ESS, a VCN production is being investigated at a geometrically more extended neutron source. The collaboration with this group is expected to be extremely valuable to exchange ideas to finally optimize the moderator-reflector design for the different source types and geometries.
In collaboration with S-DH GmbH a prototype of an extraction beamline for VCN can be developed and brought into operation at the JULIC neutron platform (prototype for the HBS neutron source) as a proof-of-principle for further compact neutron sources with higher power levels.