Ooh interesting, although that is a very low conc.
First the volume for a sphere = 4pi/3 r ^3
You would need the volume to be 1.67 x 10^36 dm^3 for there to be one mole there which is 1.67 x 10^33 m^3 (that is riduclousy large about a million x the size of the sun)
So the radius of a sphere for a given volume is given by (3/4pi V)^1/3 which would make the radius about 7.36 x 10 ^10 m or 73600000 km (about the distance to mars)
This questions seems a non-sequitir are you sure the conc is correct?