Supermirror on Superpolished Copper Reduces Background from ESS Target

Recently, Phil Bentley et al.(affiliated with the European Spallation Source ESS) have demonstrated by means of Monte-Carlo simulations (MCNP5) that Cu reduces the flux of fast neutrons emitted from the tungsten target of the ESS much more efficiently than steel. For this approach and to reduce the fast neutron background further, SwissNeutronics has developed a superpolishing process to make Cu suitable as a substrate for supermirror coatings. The reflectivity of supermirror on Cu shows (Fig. 1) a similar reflectivity as obtained for typical substrates for neutron guides such as borkron glass and aluminum. These new developments put SwissNeutronics into the position to provide robust Cu-guides for the biological shielding without requiring a gap between the neutron reflecting substrate and the surrounding bulk shielding thus eliminating streaming of high energy neutrons. In addition, the cooling of the substrates is facilitated as Cu is an excellent thermal conductor. Clearly, ESS and other spallation sources will strongly profit from supermirror coated Cu-guides from SwissNeutronics as the costs for shielding can be significantly reduced.

Fig. 1: Reflectivity of supermirror m = 3 on superpolished Cu as manufactured by SwissNeutronics.