A directional measurement device has been designed to determine the radon migration in the ideal condition. Both horizontal and vertical migration of radon are studied. The horizontal migration coefficient of radon is 0.024 cm2·s–1
which is much less than 0.1 cm2·s–1
the diffusion coefficient of radon in the air given by the references. The vertical migration coefficient of radon is 0.182 cm2·s–1
which is considerably greater than the diffusion coefficient of radon in the air.