In the last blog I wrote about how doubling the dimensions of a figure quadruples its area, tripling the dimensions quadruples the area, and quadrupling the dimensions would increase the area of a figure by a factor of 16. In general I talked about how if I multiplied the dimensions(length and width) by a factor k, the area of the new figure would be k2 times as large as the original. Here is an application to physics and the situation in Japan. Suppose that if you stand 1 foot away from a certain source of radiation that it will kill you. How intense is the radiation 100 feet away or 5000 miles away? To understand the answer think of the radiation as it radiates outward. The diagram below illustrates.
As it spreads from its source the radiation is spread over a larger and larger area. Even if none of the radiation is absorbed, it decreases in intensity as the rays or particles move outward because they are spread over a larger area. The intensity or concentration of the radiation as you move away from the source will depend on the area radiation is spread out over.
If I am twice as far away I will experience one fourth the intensity. If I am 3 times as far away, I will experience one ninth the intensity. If I am 100 times as far away, I will experience a 10,000th of the intensity. Something that is deadly a few feet away may be harmless 1000 feet away. So, at 5000 miles away(the approximate distance between Japan and San Francisco) there is little to be concerned about.
Of course, at this point I should mention that the main concern is not the radiation from the source, per se, but the spread of particle contaminates. These are physical bits of dust containing radioactive and toxic substances. Most of particle contaminates can be removed by simply taking a shower. However, a much larger problem occurs when the dust is ingested an becomes lodged internally in your lungs, through an open wound, or ingested. Particles lodged in biological tissue can act as a source of radiation internally that can cause damage over time. The dispersion of physical contaminates is not always uniform and can show up in pockets.
As a side note, it should also be noted that your body is designed to handle a certain amount of radiation. Radiation itself is not a manmade phenomena, but one that was discovered as part of nature and harnessed for human purposes. As a natural phenomena it already exists in the food we eat, the water we drink, and in the air we breathe. Even in the absence of modern civilization there would be radioactive substances in your body, but probably not toxic amounts.
