Metallic Substrate for Neutron Guides
Glass is sufficient for most applications in neutron optics. But in some cases there is a need for a more resistant, less fragile and brittle substrate. Due to its fragile character, glass can be a safety issue for neutron sources.
Metals are a promising alternative, they are more resistant, open new possibilities for neutron optic designs since they can be milled with more variety and screws can be used for assembly. Unfortunately metals are harder to polish than glass.
After a few years of development we came up with a process to polish metals to a glass like roughness and are able to build neutron guides with metallic substrates. These guides are often used for the in-pile parts close to the neutron source.
Neutron guides that are further away from the neutron source should be able to absorb not reflected neutrons that transmit through the substrate. We were looking for a solution for metal substrate, similar to the corresponding glass guides with boron content.
In tight collaboration with the ILL (Institute Laue-Langevin) we developed a borated aluminum alloy (AluBor) with a Boron content up to 20%wt. Our m=2 coatings reach 93% neutron reflectivity and we have manufactured many guide units of this material.
A neutron guide made of AluBor could be pumped directly. So the higher price for the material might be compensated by the cost savings from the elimination of the vacuum housing.
Copper is the second metal we are able to use for neutron guides. Due to some shielding advantage for fast neutrons, the ESS has specified copper as the best substrate material for the in-monolith guides. For that reason we developed the copper polishing up to the same surface quality than polished glass.