Tag: Operation Plumbbob

Would you stand under a nuclear blast?

By Phil Plait | July 24, 2012 7:00 am

As a rational human, I’m aware of finding my emotions and prejudices conflicting quite often with my knowledge of science and reality. Being reasonable is relatively new to us apes, and a hundred million years of evolving reactionary emotions usually takes precedent.

So I find myself pretty conflicted about his video, which shows five men in July, 1957, standing around in the Nevada desert while a nuclear weapon is detonated above their heads.

[Note: the video says the detonation was 10,000 feet above their heads, but that is erroneous; it was more than 18,000 feet.]

This video comes from NPR via my own Discover Magazine. [Given what follows below, I'll note that the NPR article shows that these men were not adversely affected by the blast, and most lived to be old men. I strongly urge you to read that entire article, in fact. It's fascinating.]

When I watched the video, my feelings were curious. My first reaction was visceral: basically just "Aiieeeeee!"

But that was immediately followed by, "Well, the blast was low yield and about 18,000 feet up, so the odds of them getting hurt by it were pretty small."

The thing is, both thoughts are right! Here’s why.

The blast was indeed a small one. It was not a fusion bomb (usually called a thermonuclear or H-bomb), but instead was a fission bomb, an A-bomb. These release far less energy when they explode, though it’s nothing to be trifled with. This particular test was done using a 2 kiloton yield; in other words, it exploded with the energy of 2000 tons of TNT. For comparison, the only two atomic weapons used in wartime – by the US over Hiroshima and Nagasaki – had yields of about 13,000 and 21,000 tons of TNT. Hydrogen bombs have yields typically measured using megatons, or millions of tons of TNT.

So the explosion in this video was bigger than a usual conventional bomb, but not nearly as big as what we normally think of as a nuclear bomb. Right away we have to be careful how we think of this!

Second, the explosion was at a height of well over 5 kilometers (3 miles). As I pointed out in a recent BAFact, Earth’s air is quite good at absorbing various types of electromagnetic radiation (a fancy name for "light"), including X-rays and gamma rays. The men under the blast probably received no direct dose of ionizing radiation in that form. It’s possible the intense high-energy light from the bomb created secondary forms of radiation – high-speed electrons and so on – but again, the bomb yield was low, so all that air probably did a pretty good job stopping all that.

Third, what about fallout? This is radioactive material from the blast that falls from the sky. In an atomic (or an H) bomb, radioactive atoms are created and dispersed. In low altitude tests, the heat from the explosion can draw up dust from the ground, mix it with these materials, and create a radioactive cloud that can travel a long way. Raindrops can form, and the radioactive brew can literally fall out from the sky.

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