Food that is grown in radioactive soil, or that has not yet been harvested when, fallout falls on it is another matter. This food will absorb the particles of radioactive matter into its own structure and thus become dangerous.
The biological food chain acts as a marvelous strainer and concentrator of radioactive isotopes. This was well demonstrated in certain tests that took place at Almagordo. From some intentional surface bursts and because of the unintentional venting of some underground bursts there was some fallout carried onto the milkshed for southern Utah.
The amount of fallout deposited over the surface was so slight that the most selective instruments could not detect it. An atomic or nuclear explosion releases its great amounts of energy by changing some matter into energy. It also changes certain amounts of matter into new and different types of matter. Without going into detail about atomic theory, the nature of the atom with its electron rings, and its nucleus consisting of protons and varying number of neutrons, let us simply say that these new forms of matter are generally unstable isotopes. That means they are going to change into another form of matter.
Once again, the matter, in the process of changing from one state to another, releases certain amounts of energy. It is this energy that we measure as radioactivity. The energy, depending upon the isotope involved, may be rapidly dispelled or it may continue to be released for a very, very long time. Most unstable isotopes release their energy and transform into a stable state within fractions of a second or at least within minutes after a nuclear explosion. Others take hours, and still others days, weeks, or months. Some take centuries.
Each isotope starts out with just so much energy. For all practical purposes we can say it is not going to get any more. Once that isotope has released all its excess energy it will become stable. Since the isotope releases its energy at a specified rate we can say how long it will take to lose half of its energy. After that, it will then take the same length of time again for it to lose (give off) one half of the remaining amount of energy. Question: When will all of the energy be given off by the isotope?
An ancient Greek philosopher posed the same problem. He said, "Suppose there is a bear at the back of a cave. On the first day the bear walks halfway to the entrance. On the next day he walks half of the distance that remained to the entrance after the first day. And on the day following the bear walks half of the distance that remained to the entrance from the previous day. The bear continues to do this same thing on each subsequent day. He walks half of the distance to entrance of what was left from the previous day. The question is: when will the bear get out of the cave?"
The answer is: "Never." This sort of regression is what mathematicians call asymptotic. That is to say the figures continue to approach zero, closer and closer, but they never reach it. So just as the bear never gets out of the cave, all of the energy is never lost. But much (one half) of the energy is lost in the first half-life. And three quarters of the energy is lost by the end of the second half-life. After ten half lives a very large percentage of the energy is gone.
It is because so much of the energy is lost in the early periods (half-lives), as compared to the later periods, that it is important to be in shelter during the early periods after fallout has fallen. We might divide the half-life times of radioactive isotopes into three categories. Very short term, medium term, and very long term.
As mentioned earlier, most of the unstable isotopes generated by an atomic or nuclear explosion are very short term. They give off all their significant amounts of energy in a matter of seconds. Unless you are within very close range of an atomic or nuclear bomb there will be no way for this radiation to reach you. It was this initial radiation that caused the horrible radiation burns and sickness at Hiroshima and Nagasaki.
First the good news. There will not be any persons subjected to long suffering from the initial radiation by the nuclear weapons of today. The bad news is that the reason why is that the weapons blast such a large hole or create such a large area of complete destruction that the initial radiation can't escape. That is to say the totally destructive blast extends beyond the range of the initial radiation.
On the other hand, the survivors of Hiroshima and Nagasaki did not have much problem with fallout. The first major victims of fallout were some fishermen many, many miles downwind from the Bikini Island tests. Fallout is a phenomenon much more associated with nuclear weapons.
Nevertheless, there was fallout in Southern Utah. As stated before, it was so slight it could not be detected by the most sensitive instruments. The specific matter of interest in southern Utah was the isotope 131 of iodine. This was absorbed by minute bacteria in the soil. In the process of filtering the iodine out of the soil the bacteria greatly concentrated it.
The bacteria were absorbed by legumes and other biological forms higher in the food chain. Each in turn further concentrated the iodine isotope.
Finally, after the iodine had found its way into the grass a cow came along and ate it. Now a cow is a very complex organism in itself. There are all sorts of biological activities going on in a cow. Various organs and the bone marrow filter out different minerals for different purposes. One of these complex systems forms milk. This particular cow, and hundreds of others like it, was milked, and the milk was bottled and distributed to children all over the area of southern Utah.
The children were also complex biological organisms. They in turn had numbers of specific organs that specialized in straining out various minerals and compounds from the food that they consumed. The end result was that their thyroids once again concentrated the iodine 131. And this to such an extent that if you held a radiation detector next to their necks it buzzed like a rattlesnake. This was not healthy.
In fact numerous problems developed among the population. There were a great number of mentally retarded children born, and a number of other unpleasant ramifications. This need not have occurred from the iodine 131 if we had known what we know today.