Semi-continuous measurement of the unattached radon decay products size distributions from 0.5 to 5 nm by an array of annular diffusion channels

A new diffusion battery was designed to make precise measurements of the indoor activity size distribution of short-lived 222Rn decay products in the size range of 0.5–5 nm. It relies on the selection of particles by five annular diffusion channels (ADCs) and on the use of a non-linear inversion method, EVE, for the reconstruction of the particle size distributions. The ADC geometry proved to allow a better selection of the particles size compared to the wire screen and the implementation of an alpha detector set in front of the sampling filter for semi-continuous activity measurements. EVE algorithm was chosen in order to take into account the uncertainties of the measurement in the deconvolution process. The diffusion battery was tested in a radon chamber, and results showed a good reproducibility of the measurements. The degree of confidence on the obtained size distributions is then discussed. Results show that the relative uncertainty on the penetration data has to be less than 10% in order to obtain a reliable size distribution.