What is Radioactive Fallout?

Lots of panic going on - even halfway across the world from Japan -- about nuclear meltdowns, etc. So... what exactly is a radioactive fallout? This is an interesting excerpt from a website (http://www.ki4u.com/guide.htm) I found online a while back, and thought it might prove helpful to you:

Radioactive fallout is the particulate matter (dust) produced by a nuclear explosion and carried high up into the air by the mushroom cloud. It drifts on the wind and most of it settles back to earth downwind of the explosion. The heaviest, most dangerous, and most noticeable fallout, will 'fall out' first closer to ground zero. It may begin arriving minutes after an explosion. The smaller and lighter dust-like particles will typically be arriving hours later, as they drift much farther downwind, often for hundreds of miles. Once it arrives, whether visible or not, all that will fall will have done so usually in under an hour, then blow around everywhere just like dust does on the ground and roofs. However, rain can concentrate the fallout into localized 'hot spots' of much more intense radiation with no visible indication.



This radioactive fallout 'dust' is dangerous because it is emitting penetrating radiation energy (similar to x-ray's). This radiation (not the fallout dust) can go right through walls, roofs and protective clothing. Even if you manage not to inhale or ingest the dust, and keep it off your skin, hair, and clothes, and even if none gets inside your house, the radiation penetrating your home is still extremely dangerous, and can injure or kill you inside.



Radioactive fallout from a nuclear explosion, though very dangerous initially, loses its intensity quickly because it is giving off so much energy. For example, fallout emitting gamma ray radiation at a rate over 500 R/hr (fatal with one hour of exposure) shortly after an explosion, weakens to only 1/10th as strong 7 hours later. Two days later, it's only 1/100th as strong, or as deadly, as it was initially.