Improvements in the Sample Space for the Backscattering Silicon Spectrometer (BASIS)

The increase in neutron flux at the Oak Ridge National Laboratory (ORNL) Spallation Neutron Source (SNS), currently operating at 2.0 MW proton beam power, has created new opportunities for higher-throughput neutron scattering experiments while also increasing the importance of minimizing background scattering and optimizing sample-environment operations. To address these challenges faced by the Backscattering Silicon Spectrometer (BASIS), several upgrades were developed and evaluated, including boron carbide (B4C) masking for flat-plate sample containers, multi-cell sample holders used with a vertically translating sample stick, and an automated helium pump-and-purge (HPP) system for closed-cycle refrigerators. Neutron diffraction measurements demonstrate that B4C masks reduce background scattering by 49–67%, outperforming both borated aluminum and boron nitride masks while introducing no additional Bragg reflections within the instrument’s accessible Q-range. Commissioning tests of a double-cell flat-plate sample container showed no measurable crosstalk between adjacent sample compartments and confirmed a stable thermal performance, enabling multiple samples to be measured without repeated temperature cycling. In addition, the automated HPP system provided reproducible sample-space gas handling with approximately ±1 mbar precision while reducing the need for operator intervention and supporting remote operation. Together, these developments improve signal-to-noise performance, increase experimental throughput, and enhance operational efficiency at BASIS, supporting the instrument’s continued operation under higher neutron flux conditions.