Indoor radon progeny particle size distribution measurements made with two different methods

Indoor radon progeny particle size measurements using two distinctly different instruments, a diffusion battery and an electrical aerosol size analyser, were carried out in two single-family homes in New Jersey. The activity-weighted size distributions were determined by applying the radon progeny attachment theory to the measured number-weighted particle size spectra and the results are close to those measured by the diffusion battery method. These particle size distributions were found to be more often bimodal than unimodal. The minor modes of the bimodal distributions were located around the 1 nm region, close to the 218Po atom size, except one centred around 10 nm. For both the unimodal and the bimodal distributions, the modal diameter of the major mode ranged from 30 nm to 150 nm, respectively. The results previously reported showed modal diameters around 100 nm. (author)