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.
Well, it’s been a while coming, but I’m pleased to let y’all know that the third and final episode of "Bad Universe" will air on The Discovery Channel tomorrow, April 19, at 11:00 a.m. Eastern (US) time — but of course, check your local listings.
The episode is entitled "Death Stars", and is about the effects of solar flares and nearby supernovae. Like the other two, this was a lot of fun to put together, though the trip to Sandia Lab still haunts me a bit… but I won’t give that away. You’ll just have to see. I actually haven’t seen the final cut since we put it together late last year, so to be honest when I watch it tomorrow it’ll be a bit like seeing it again for the first time.
Speaking of which, my daughter will be in school when it airs, so I won’t watch it until we can see it as a family. That means I won’t be live-tweeting or anything like that.
And to answer the inevitable question: I don’t know if the network is picking it up as a series or not. I expect the ratings of the airing tomorrow may play into that, so tell a friend! Or tell a few dozen.
I hope you like it, and have at least as much fun watching it as I did making it.
Randall Munroe, who draws the geekerrific xkcd webcomic, has created a really good chart showing relative radiation doses absorbed by humans doing various activities.
I’ve put a piece of it here, the section with the lowest doses. I like this! A lot of folks don’t understand what radiation is — light is radiation, for example — or that just by existing on the surface of our planet you absorb a certain amount all the time: from the ground, from space, from things you eat. Wikipedia actually has an excellent rundown of what radiation is, and the critical distinction between ionizing and non-ionizing radiation (there’s also electromagnetic versus subatomic particle radiation, but that’s less of a concern here).
In the chart, Russel deals with doses from ionizing radiation. This is the kind that can cause damage… but only in sufficiently high doses. For example, bananas are a natural source of gamma rays due to the decay of an isotope of potassium (40K). It’s a pretty weak source — a few years back I had access to a gamma-ray detector and we could barely detect a banana’s emission — and it doesn’t affect you in any real way. Potassium iodide is a common salt that’s also a gamma-ray emitter, but again you’d need a lot of it for it to be dangerous… and if you ate that much you’d have worse issues!
The average amount of radiation you absorb in a year is about 3 – 4 milliSieverts, depending on where you live. At higher elevations — like, say, Boulder, where I live — cosmic radiation puts you on the higher end of that scale. I’ll note that cancer risk is not really higher living up here than at sea level (lung cancer rates are lower than average here, probably due to the healthy lifestyles most people follow in Boulder, but skin cancer rates are slightly higher than average, probably due to a combination of people being outside more than average together with the thinner air blocking less UV).
In general, you can actually absorb a much higher than usual radiation dose (up to a point, of course) without ill effects, since your body can heal some amount of damage (just like it heals from a cut). Too many such doses too close together, or too big a dose all at once, can do too much tissue damage and be fatal (I guess, again, like a cut). For example, I like to point out that the Apollo astronauts got roughly a year’s worth of radiation absorption in their tissue while voyaging to the Moon and back, but didn’t suffer any ill effects.
Obviously, this is a complicated issue, but the xkcd chart looks like a pretty good way to eyeball where things fall on a scale of "nothing to worry about" to "AIEEEEPANICPANICPANIC".