Softened up a planet before invading with some orbital bombardment. Then after I dropped my troops, the aliens launched a ship that managed to bombard my forces on the planet before I destroyed it. Anyway, once I finally conquered the planet, the surface radiation was about 91, and over the course of a few months, the civilian population has been halved (down to 250 million from over 500 million.)
Is there any way to reduce surface radiation apart from time? I'm trying to put in infrastructure to provide shelter, but it's not helping either. At least the population has a 1.5% increase, so it's no longer a mass die-off.