A passive integrating dosimeter with two diffusion cups was applied for detecting 222 Rn and 220 Rn simultaneously. To let both nuclides enter in easily
one of the cups had membrane with higher permebility. However
the other cup with lower permeability membrane could only allow the entering of 222 Rn. Hence
222 Rn and 220 Rn can be detected simultaneously by such dosimeters.