You Might Want to Know: What’s “fallout”? A primer.
When a nuclear bomb explodes in the air, it produces terrific heat and blast, of course, but also something that was new for a bomb: a blast of ionizing radiation. The nuclear fission that has produced the energy for the heat and blast also produces that blast of ionizing radiation. The same process also produces hundreds of elements called “fission products,” atoms that the nuclear fission has made radioactive, meaning that they too now emit ionizing radiation. These may also be called “radionuclides” or “radioisotopes,” which can be confusing.
A nuclear weapon always produces these fission products. If the bomb’s fireball has come into contact with the earth or water, a very much greater number of fission products will be produced. Some of these will remain close to Ground Zero. Some will be carried away in the wind and fall somewhere, maybe a lot of them, maybe not so much.
It’s now known that more than two hundred different kinds of fission products are produced in a nuclear explosion. Some are radioactive for only parts of seconds, some for minutes, some for months and years. To talk about how long something will be radioactive, it’s customary to talk about the “half-life” of the radioactive element. The half-life of a radioactive element is the amount of time it would take for it to lose half of its radioactivity, then half of what’s left and so on. It’s a steady process and can’t be affected by anything we do.
The radioactive fission product iodine-131, for example, has a half-life of eight days, strontium-90 a half-life of twenty-eight years, and cesium-137 a half-life of thirty years. Plutonium-239, which is radioactive, is a not a fission product but it will be present in fallout when plutonium has been used as the fissile fuel. Plutonium is highly dangerous to inhale, even in tiny amounts. It has a half-life of 24,100 years. It would be dangerous for ten times that long.
The fission products that are carried off by the wind are deposited later, somewhere. Wherever the wind, and the rain, will. Are we going to be to predict where it will get deposited? The weather forecasters can give some guidance here, and they were asked to do so by the Atomic Energy Commission during the era of atmospheric testing. But you know how it is with weather forecasting. It deals in probabilities. No one will know for certain where the fallout will show up.
Depending on the power of the nuclear detonation some of the fission products may be, and were, propelled up above the atmosphere, into the stratosphere--above the weather. Gravity will make these fission products fall out some time but now we really don’t know when or where.
Above-ground nuclear detonations stopped in 1963, mostly, because of the Atmospheric Test Ban Treaty, signed by the United States, the Soviet Union, and the United Kingdom. France didn’t sign until they had finished testing their bomb. By now, we are told, sixty years later, most of the fission products thrown up into the stratosphere by the tests have returned to earth.
We need to be protected from larger amounts of fallout because we need to be protected from ionizing radiation (more about why in the earlier postings on ionizing radiation).
Different fission products will be dangerous in different ways because of what kind of ionizing radiation is being emitted and because different elements behave differently on and in our bodies. Beta radiation can produce burns on the skin. Alpha radiation, which is what plutonium emits, won’t do that. X-rays will penetrate deeply. Gamma rays even deeper. The deepest of all. A foot of concrete won’t stop them.
Ingested iodine, which emits mostly beta radiation, tends to end up in our thyroid glands. Cesium, mostly beta but some gamma, tends to end up in the pancreas. Strontium, which also emits beta radiation, has been called a “bone-seeker” because that’s where it tends to get concentrated. So the incidence of thyroid cancer, pancreatic cancer, and bone cancer and leukemia can be expected to rise depending on which element is in the picture.
The elements can also be taken up by the grass and the animals that eat it. And by the people that eat those animals.
Another important consideration here is biological half life. Elements that are taken into the body are also excreted by the body. The biological half-life is how long the radioactive element can be expected to be doing its work in the body before excretion or radioactive decay reduces its power by half. Different elements will have different biological half-lives.
Quite a lot to think about here, isn’t there? It took scientists and doctors a long time from the discovery of radioactivity and fallout to learn most of what I’ve just laid out.
If we should run into some fallout, we wouldn’t be able to tell how much ionizing radiation we had been exposed to unless we happened to have a dosimeter on us. We probably wouldn’t have gotten an immediately lethal dose from fallout unless we happened to have spent some time in a hot spot (where a concentrated amount of fallout had been deposited by rain or weather) or gotten a good bit of fallout on us and left it there for a while.
If we’ve gotten an immediately lethal dose, we’ll know in an hour or so, a couple of days at most. If we haven’t gotten an immediately lethal dose, we may get sick later and die, or get sick, even very sick, and not die, like the Japanese fishermen after the Bravo test, or not even get sick. Not right away. Maybe later, with cancer. And maybe never. That’s the thing about radioactivity.
The higher the dose, the greater the likelihood of death. But which of those who don’t get an immediately lethal dose will die? No one is going to be able to tell us. It will be possible to predict a rough number, a range, but not who specifically will die from a non-lethal dose of radiation.
There’s a lot to think about here. And many unknowns that will almost certainly remain that way.
It’s good there has been no testing in the atmosphere, or just a little, since 1963.
Next: The Fallout Chronicles - I. First Observed Effects
The next several postings will be entitled The Fallout Chronicles. Fallout is usually treated as a technical matter. The current entry does that. The next several postings will look at fallout historically. The story that will emerge can be read in more than one way. But it is not a tale likely to make us proud of our Cold Warriors.