Radiation is something that any vault-dweller must be concerned with. While it is normal for a small amount of roentgens, or rads, to enter the normal person during the normal year of activity (more if activities include mountain expeditions and/or high altitude ballooning), a large amount of rad poisoning is a reason for concern. The average person receives about 1/2 to 1 rad a year. After a nuclear fallout, you would expect more. With any exposure to radiation, your radiation resistance will reduce the total amount of rads you take by it's percentage. It is very similar to damage or poison resistance.

Initial Level: Starting radiation resistance is equal to your Endurance x 2. Average characters will have a 10% radiation resistance.