Humidity Chambers

BerILL is a humidity chamber for neutron scattering that uses the temperature control technique to induce humidity on a sample with excellent accuracy and ease of control. The relative humidity (RH) and temperature at the sample are controlled by regulating the partial vapour pressure of a connected water bath via its temperature, independently from the sample area. Both temperatures are controlled via two chiller thermostats in an easy automated way. The temperature stability, precision and homogeneity are improved with a resistive heater driven with additional controllers.

With the neutron diffractometers V1 (HZB) and D16 (ILL), we validated the chamber performances by monitoring the d-spacing changes of DOPC and DMPC bio-membranes that show a significant and well-known swelling behaviour, especially at high humidity conditions. Although these membranes equilibrated immediately below 95% RH, the intrinsic equilibration process was remarkably slower than the vapour equilibration in the humidity chamber. Nevertheless, we could prove that the new chamber operates remarkably well up to 99.7% RH.

The temperature stabilities measured at the sample and in the water bath are better than 2 mK, which resulted in a stability of the induced RH of about 0.01%. The temperature equilibration time in the cell is in the order of 30 min. The variation of the RH across the sample is given by the temperature gradient mostly created by the temperature difference between bath and sample. Null at 100% RH, this gradient increases to less than 1% towards 0% RH.

Several copies of BerILL were built for HZB and ILL. It is now foreseen to produce different variants based on the same principle but optimized for different scattering techniques.