Twenty years ago, America was diagnosed with “Nuclear Fear.” Specifically, a small claque of left-leaning shrinks and psychologists decided that anxiety over nuclear war was responsible for everything from declining SAT scores to rising suicide rates – from family breakup to cosmic Loss of Meaning.

Nuclear Fear, to the extent that it ever existed, vanished along with the Cold War. Now it seems that something akin may be back, at least when measured by the bombardment of nervous questions directed by citizens to Doctors for Disaster Preparedness. As physicians, we’ve already provided some facts on the biological threat in this space. As radiologists, we now address some of the perils related to nuclear explosions and the release of radioactivity by other means. Here’s what to do, and to remember.

Don’t panic.

The single most important question – Where are you in relation to the release of radiation? The national media will doubtless provide a great deal of initial information, much of it wrong. You may have to rely on local sources. Ideally, television and the Internet could present relevant data in the form of weather graphics, but they may be too busy to prepare them. We hope that enough measuring instruments, and people who know how to use them, will soon be available throughout the country. It’s probable that any terrorist use of nuclear and radiation-releasing devices would occur in major population centers. Still, no matter where you are, you’ll need to know.

But information without context can be meaningless, or worse. It’s vital, therefore, to understand the facts about radiation, and their implications for survival.

Remember that radiation is invisible and does not produce an immediate effect. It comes in two general kinds: direct and residual, aka, “fallout.” If you haven’t been exposed to the other impacts of a nuclear explosion – heat, light, blast – you may not have been exposed to the direct radiation: x-rays, gamma rays and neutrons. You probably have hours or even days to deal with the situation.

Remember also that a conventional explosion may be used to release radioactive materials, or the material merely scattered about. You may never see a mushroom cloud.

Keep this in mind about radiation. Everyone on earth lives in a continual bath of radiation – small additional doses are harmless. Larger doses – thousands of times higher than normal – can sicken and kill. Dosage determines lethality.

Radiation from fallout (particulate matter made radioactive, either by nuclear explosion or other exposure) comes in many varieties. Many decay rapidly. Some linger, but at very low levels. All fallout disperses with prevailing winds, and is washed out of the atmosphere by the rain. If you’re hundreds of miles upwind and it’s raining, you’re probably safe.

If you’re downwind, or have reason to believe that you might be seriously affected, what to do?

Don’t panic.

Try to determine whether it’s safer to leave or stay put. Leaving may come in two forms. One may be government-directed and panicky. The other may be spontaneous and panicky. Lots of anxious people crowding the roads are guaranteed to produce, if nothing else, lots of auto accidents. It’s easy to imagine a repeat of the Three Mile Island panic in which at least one person was killed in an auto accident while fleeing the area while not a single person suffered so much as a nose cold from the radiation.

If staying put is best, you’ll be wishing you had that object of 1960s (and subsequent) ridicule: a fallout shelter. Sadly, the United States has never taken civil defense seriously. Other countries have and do. Switzerland, for example, has shelter space for the entire population. Israel quietly requires intense preparations. Only now are we realizing how much effort and treasure the Soviet Union (no strangers to devastation on their own soil) spent on their effort. You might consider building a shelter now, or going in with friends and neighbors. You’ll need to stock it with the usual provisions, plus iodide pills to prevent thyroid damage from radioactive iodine.

Finally, remember that unless you’re awfully close, a terrorist event involving radioactivity is eminently survivable. Anyway, the better prepared you are, the luckier you’ll get.

Twenty years ago, the “Nuclear Fear” crowd played a curious game: They flaunted fear as some sort of higher reason and morality. To the extent that you trembled before the Bomb, you were a good and sensitive person. But fear didn’t win the Cold War. Courage did. And courage, not fear, will prevail again.

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