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.

However, waiting for one hour cures 6 Rads. If you cannot fast travel, waiting might be useful, therefore increasing the usefulness of this perk.

Players with the Child at Heart perk could consider trading for cave fungus in Little Lamplight, and players who have Point Lookout should consider the abundant Punga Fruit the  Point Lookout DLC brings as alternatives to this perk.

Also, by level 28, you should have enough Radaway/caps to buy Radaway to make this perk almost useless.