Theoretical foundation for a simple method for simultaneous measurements of the unattached fraction and activity median diameter of attached radon progeny.

Calculation of lung dose from established lung dosimetry models requires use of the unattached fraction of potential alpha energy concentration (PAEC) of radon progeny and the activity median diameter (AMD) of attached radon progeny, in addition to the total PAEC. In the present work, for indoor environments without the nucleation mode of aerosols, a method based on the wire screen penetration theory using two wire screens and a filter is proposed for simultaneous measurements of these two parameters. It is shown that the traditional wire screen method can overestimate or sometimes underestimate the unattached fraction, depending on the properties of the wire screen and the true unattached fraction. The present method eliminates such uncertainties.