Rad Absorption (Broken Steel)

 is a perk added to Fallout 3 with the Broken Steel add-on.

With this perk, your Radiation level slowly decreases automatically over time (1 rad every 20 seconds). The actual effectiveness of this perk varies, because mostly, player characters at a level this high will have a house with a My First Infirmary that can instantly cure all rads. It's as simple as fast-traveling to the house, curing all rads, and returning to whence you came, and you won't have wasted a perk.