Optimization of focusing supermirror neutron guides for low γ-background

Abstract Supermirror coating is a significant source of γ -radiation in neutron guide systems, which can cause serious problems at instruments by increasing the γ -background . This problem is more stringent in case of γ -sensitive signal detection, like PGAA or in-beam Mossbauer spectroscopy. Shielding possibilities close to the sample are limited, but guide shape has significant effect on the number of γ -photons produced in this region. To develop good γ -shielding and guide system we have to understand the source and transport of γ -radiation in neutron guides and surrounding shieldings. We have developed a program which integrate VITESS and MCNPX to calculate the γ -background . We compared the simulated γ -background and guide performance with measurements on real focusing guide configurations.