Just read Radiation Protection Factors for Dummies – by L.H. on your blog. These types of articles always talk about shielding of radiation. Is there any substance that REFLECTS radiation instead of absorbing it?
JWR Replies: It has been nearly 20 years since I took the Army NBC Defense Officer’s course, so forgive me if any of the following betrays my faulty memory: Any of the materials described will reflect or absorb alpha or beta radiation, and absorb highly energetic gamma rays. Because they are a ray (think of it as a flash from a flash bulb, or the beam from an x-ray machine), virtually nothing will reflect gamma rays. Once gamma rays have been stopped by shielding, they are no longer a threat. But the gamma ray emitter–typically a fallout dust particle, continues to emit gamma for a very long time.
Alpha radiation has a very short effective range and is rapidly attenuated by passage through the air. That makes it a non-issue for your survival planning. Beta has longer range, but just a sheet of cardboard will stop beta radiation. (Beta radiation mainly causes injury to the skin that looks much like a sunburn–commonly called “beta burns.”) It is mainly the gamma radiation that you have to worry about. That requires a lot of thick shielding. (You need mass—any mass–and a lot of it!) Fallout dust itself continues to emit alpha, beta, and gamma rays for many, many months. That is why, assuming that you will be using a shielding-improved basement type shelter, that it is important to close and seal your house windows after the blast wave(s) passes. If they are shattered by the blast wave, you should cover the broken windows with sheet plastic and tape seal them before taking shelter in your basement shelter, during the brief time available in the “King’s X.” (The short period between the blast/shock wave and the time that the fallout dust begins to settle.) After shelter emergence, it is possible to decontaminate your roof and sidewalks by hosing the fallout dust away (while wearing the proper protective gear, naturlich), but it will be almost impossible to decontaminate the interior of your house if it has been coated with fallout dust. Read the book Nuclear War Survival Skills –available for free download from the Oregon Institute of Science and Medicine  web site, for details.