A New Dew-Point Hygrometry Making Use of β-Ray Scattering

Abstract

The present hygrometer is devised on the principle that the β-ray scattering by the metal surface decreases when the surface is covered by dew. This decrease of β-ray scattering is caused by the decrease of the effective atomic number of the scattering surface material. Carbon-14 and gold plate were used as the β-ray source and the metal, respectively. The counting rate due to scattered β rays and the temperature of the plate surface were recorded against time. The two temperatures at which the dew begins depositing and disappearing were detected in the experiments and decided the same dew-point.
This hygrometer is useful to prevent supersaturation, because numerous condensation nuclei are formed by β rays and the rough finish of the plate surface makes the formation of dew easy. The hygrometer is also free from the errors owing to the incidental rise of the surface temperature caused by illumination which is indispensable for the mirror type hygrometer.
The dew-point could be measured to an accuracy of 0.5°C, i.e. 2% in humidity, at room temperature.