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Nuclear Bomb vs. Dirty Bomb: What's the Difference?

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The Quick Trick: If you're standing in an absolute wasteland amid thousands of corpses, it was a nuclear bomb. If you're standing in a normal city street amid a moderate amount of inconvenience, it was a dirty nuclear bomb.

The Explanation: Here is the primary difference: Nuclear bombs have, in the past 70 years, killed hundreds of thousands of people. Dirty nuclear bombs have, in all of human history, killed exactly no one—partly because they aren't terribly dangerous and partly because not one has ever been detonated.

Conventional nuclear weapons get their explosive power from either nuclear fission or fusion. The bombs dropped on Hiroshima and Nagasaki—the only nuclear weapons that have been used in warfare—were both fission bombs. Fusion bombs, sometimes called hydrogen bombs, are even more powerful—the U.S. once detonated a 15-megaton fusion bomb in a test. That's approximately 100 times more powerful than "Little Boy," the nuclear weapon dropped on Hiroshima that instantly killed 100,000 people. Most modern bombs combine fission and fusion: a small fission bomb is used to create heat adequate to fuel the
fusion.

Even with the physics know-how, the bombs require exceedingly rare isotopes of either plutonium or uranium. The process of getting the elements to the necessary isotope is known as enrichment, and enrichment is generally the stumbling block for nations looking to join the nuclear club. It was even a challenge for the U.S.: Almost 90 percent of the Manhattan Project's budget was spent enriching uranium.

In short, nuclear weapons are extremely difficult to make—and we hope they always will be. A dirty nuclear bomb, on the other hand, could be made by a reasonably smart 14-year-old with access to hospital equipment. Dirty bombs combine conventional explosives (say, dynamite) with radioactive materials (say, cesium, which is used in radiation treatment for cancer patients). Almost all scientists believe that even in the case of a well-designed dirty bomb, the explosive would cause much more damage than the radiation. The fact is there just aren't any acquirable materials radioactive enough to cause much fallout. And while it could be very expensive and inconvenient to clean up an urban area after a dirty bomb attack—that's about it. The difference between the two is that conventional nuclear weapons are infinitely more worrisome.

Dirty Secrets
The only recorded attempt to detonate a dirty bomb came in 1995, when Chechen rebels—who had been on the forefront of terrorism techniques since the Soviet Union's breakup—called reporters to say they'd planted a bomb in a Moscow park. Made of dynamite and cesium taken from a cancer treatment center, the dynamite might have killed people, but its cesium would have been just the equivalent of a few X-rays for those walking past the park. Regardless, the bomb was defused before it exploded.

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The Surprising Reason Why Pen Caps Have Tiny Holes at the Top
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If you’re an avid pen chewer, or even just a diehard fan of writing by hand, you’re probably well acquainted with the small hole that tops off most ballpoint pen caps, particularly those classic Bic Cristal pens. The reason it’s there has nothing to do with pen function, it turns out. As Science Alert recently reported, it’s actually designed to counter human carelessness.

Though it’s arguably unwise—not to mention unhygienic—to chomp or suck on a plastic pen cap all day, plenty of people do it, especially kids. And inevitably, that means some people end up swallowing their pen caps. Companies like Bic know this well—so they make pen caps that won’t impede breathing if they’re accidentally swallowed.

This isn’t only a Bic requirement, though the company’s Cristal pens do have particularly obvious holes. The International Organization for Standardization, a federation that sets industrial standards for 161 countries, requires it. ISO 11540 specifies that if pens must have caps, they should be designed to reduce the risk of asphyxiation if they’re swallowed.

It applies to writing instruments “which in normal or foreseeable circumstances are likely to be used by children up to the age of 14 years.” Fancy fountain pens and other writing instruments that are clearly designed for adult use don’t need to have holes in them, nor do caps that are large enough that you can’t swallow them. Any pen that could conceivably make its way into the hands of a child needs to have an air hole in the cap that provides a minimum flow of 8 liters (about 2 gallons) of air per minute, according to the standard [PDF].

Pen cap inhalation is a real danger, albeit a rare one, especially for primary school kids. A 2012 study [PDF] reported that pen caps account for somewhere between 3 and 8 percent of “foreign body aspiration,” the official term for inhaling something you’re not supposed to. Another study found that of 1280 kids (ages 6 to 14) treated between 1997 and 2007 for foreign body inhalation in Beijing, 34 had inhaled pen caps.

But the standards help keep kids alive. In that Beijing study, none of the 34 kids died, and the caps were successfully removed by doctors. That wasn’t always the case. In the UK, nine children asphyxiated due to swallowing pen caps between 1970 and 1984. After the UK adopted the international standard for air holes in pen caps, the number of deaths dropped precipitously [PDF]. Unfortunately, it’s not foolproof; in 2007, a 13-year-old in the UK died after accidentally swallowing his pen cap.

Even if you can still breathe through that little air hole, getting a smooth plastic pen cap out of your throat is no easy task for doctors. The graspers they normally use to take foreign bodies out of airways don’t always work, as that 2012 case report found, and hospitals sometimes have to employ different tools to get the stubbornly slippery caps out (in that study, they used a catheter that could work through the hole in the cap, then inflated a small balloon at the end of the catheter to pull the cap out). The procedure doesn’t exactly sound pleasant. So maybe resist the urge to put your pen cap in your mouth.

[h/t Science Alert]

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Big Questions
What Causes Sinkholes?
Mark Ralston/AFP/Getty Images
Mark Ralston/AFP/Getty Images

This week, a sinkhole opened up on the White House lawn—likely the result of excess rainfall on the "legitimate swamp" surrounding the storied building, a geologist told The New York Times. While the event had some suggesting we call for Buffy's help, sinkholes are pretty common. In the past few days alone, cavernous maws in the earth have appeared in Maryland, North Carolina, Tennessee, and of course Florida, home to more sinkholes than any other state.

Sinkholes have gulped down suburban homes, cars, and entire fields in the past. How does the ground just open up like that?

Sinkholes are a simple matter of cause and effect. Urban sinkholes may be directly traced to underground water main breaks or collapsed sewer pipelines, into which city sidewalks crumple in the absence of any structural support. In more rural areas, such catastrophes might be attributed to abandoned mine shafts or salt caverns that can't take the weight anymore. These types of sinkholes are heavily influenced by human action, but most sinkholes are unpredictable, inevitable natural occurrences.

Florida is so prone to sinkholes because it has the misfortune of being built upon a foundation of limestone—solid rock, but the kind that is easily dissolved by acidic rain or groundwater. The karst process, in which the mildly acidic water wears away at fractures in the limestone, leaves empty space where there used to be stone, and even the residue is washed away. Any loose soil, grass, or—for example—luxury condominiums perched atop the hole in the ground aren't left with much support. Just as a house built on a weak foundation is more likely to collapse, the same is true of the ground itself. Gravity eventually takes its toll, aided by natural erosion, and so the hole begins to sink.

About 10 percent of the world's landscape is composed of karst regions. Despite being common, sinkholes' unforeseeable nature serves as proof that the ground beneath our feet may not be as solid as we think.

A version of this story originally ran in 2014.

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