Time-Resolved Measurement of Droplet Size and Concentration in Cloud Chambers

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Abstract
An optical method for measuring droplet size and concentration in a cloud chamber on a time-resolved basis is discussed. During the growth of the droplets, speed transmission at two wavelengths of light is continuously measured by high-speed electronic equipment. Interpretation of the resulting transmission vs time curves is made on the bash of Mie muttering theory. The appearance of oscillatory regions in the transmission curves is related to the primary oscillations of the scattering coefficient and indicates the presence of a monodisperse cloud. Two methods of data interpretation are discussed from which absolute values of droplet silt and concentration are obtained. Final droplet diameters from 1.75–10.4 μm with corresponding concentrations from 1.80 × 106–1.15 × 104 cm−3 have been measured in our cloud chamber. The technique is applicable to condensation studies conducted in Wilson cloud chambers. We suggest that apparatus of the type described is also suitable for the absolute calibration of condensation nuclei counters of various types.

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