Die Verteilung der natürlichen Radioaktivität auf das Größenspektrum des natürlichen Aerosols

Abstract

The apparatus described allows to measure the distribution of natural radioactivity on aerosol particles. Careful measures were taken that the aerosol concentration and its size spectrum were not altered before being examined. To increase the accuracy of the measurements the natural aerosol was charged with thoron decay products. The resulting electric charge-distribution by ion diffusion on dust particles is known, therefore the radii of these particles could be calculated by mobility measurements. By means of the law, governing attachment of emanation decay products on dust particles — as derived byLassen orWieser andStierstadt (afterBricard), it is possible to calculate the size spectrum of natural aerosol from the measured activity spectrum. Until now we have onlyion spectra for the range of size 6×10⁻⁷ to 10⁻⁵ cm. With the quoted apparatus however it is possible to measure thesize spectrum of natural aerosol. So we have a simple size-spectrometer, that covers a large range of particles. Among other things can be deduced from these measurements, that the natural radioactivity of air is attached to particles of radii from 10⁻⁶ up to 10⁻⁵cm, — the main part of the activity being carried by aerosols with radii between 4 and 6×10⁻⁶cm. From the calculated aerosol spectrum (r from 6×10⁻⁷ to 10⁻⁵ cm) follows a mean particle radius ofr=2,5×10⁻⁶cm at a particle concentration of 3×10⁴cm⁻³.