Answer to Question #8706 Submitted to "Ask the Experts"

Category: Homeland Security

The following question was answered by an expert in the appropriate field:


What is the best material or combination of materials for stopping radiation? Some of my family lives in Israel where nuclear weapons are a real threat.


Your question specifies radiation that might result from a "nuclear detonation" in an urban environment as a result of a terrorist activity. 

The vast majority (80–85 percent) of energy expended from a nuclear weapon detonation is either thermal (heat) or blast. The remaining energy is expended as either prompt (immediate) radiation or the resulting fallout that emits radiation post-blast. The best way to protect yourself from either type of radiation, which is mainly in the form of very penetrating gamma and x rays, is to be in "deep" shelter; that is a shelter that has dense material between you and radiation source. It is recommended that if you observe a large, bright flash of light (that could be the detonation of a nuclear weapon) that you immediately "Duck and Cover" to protect yourself from the blast and heat. 

This involves moving away from windows and doors and covering your head and eyes. If you escape the immediate effects of the blast and heat, you should then move either to the basement or the building's interior to get as much dense material between you and the outside of the building (including the roof). Fallout, a very dangerous post-detonation effect, is in the form of a fine dust or sand-like material that will deposit on surfaces downwind of the detonation. The wind may be blowing at different speeds and directions at different altitudes, so the wind direction at ground level may not be indicative of which direction the fallout is depositing on the ground, streets, and buildings. 

Keeping yourself in "deep" shelter until the authorities have had the opportunity to survey the area (check the area for residual radiation) and make recommendations for evacuation would provide the best protection for the general population and may take up to a couple of days. If people were outside at the time of the detonation and get fallout on their person, they should as soon as possible remove their outer clothing; wash their hands, face, and hair; and then shelter in nearby buildings (that are safe to occupy) until the authorities recommend evacuation from the area.

Ken Groves

Ask the Experts is posting answers using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table. You can also view a diagram to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here.
Answer posted on 18 December 2009. The information posted on this web page is intended as general reference information only. Specific facts and circumstances may affect the applicability of concepts, materials, and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice. To the best of our knowledge, answers are correct at the time they are posted. Be advised that over time, requirements could change, new data could be made available, and Internet links could change, affecting the correctness of the answers. Answers are the professional opinions of the expert responding to each question; they do not necessarily represent the position of the Health Physics Society.