Optimization of focusing supermirror neutron guides for low y-background

摘要

Supermirror coating is a significant source of y-radiation in neutron guide systems, which can cause serious problems at instruments by increasing the y—background. This problem is more stringent in case of y-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 y-photons produced in this region. To develop good y-shielding and guide system we have to understand the source and transport of y-radiation in neutron guides and surrounding shieldings. We have developed a program which integrate VITESS and MCNPX to calculate the y-background. We compared the simulated y-background and guide performance with measurements on real focusing guide configurations.