A versatile humidity cell with static vapour and gas-flow modes for time-of-flight small-angle neutron scattering

This paper describes the design, construction and operation of a prototype humidity cell for temperature and humidity control on small-angle neutron scattering (SANS) instruments at ISIS. Flat sapphire windows were used for the low background and the compatibility with the time-of-flight for instruments at pulsed neutron sources, as well as the visual transparency. The gas tubes attached to the cell allow pressure changes (0.006–1 bar) and the incorporation of gas-flow modes into a vapour-pressure-based static cell. Multiple modes of operation could help overcome the drawbacks of conventional static humidity cells on slow relative humidity (RH) equilibration and limitations to reach low RH conditions while maintaining high RH accuracy and stability during SANS measurements.