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  • Airport security is the most awkward, confusing, and tedious part of every trip!

  • After spending an hour or so marinating in a long line, you and your bags are scanned

  • with who-knows-what kind of technology, zapped with who-knows-how much radiation, and possibly

  • wiped down with a little swab for who-knows-what reason.

  • Well, we can't make airport security suck any less.

  • But we can explain exactly what's being done to you and your bagswhat you're

  • being exposed toand how the science of security works these days.

  • When you get to the security line, one of the first things you see is probably the bag scanner.

  • The scanner uses X-rays to detect objects inside your bag, as well as how dense they are.

  • One side of the machine emits both low- and high-energy X-rays, which pass through your

  • bag and hit detectors on the other side.

  • When the X-rays pass through your bag and its contents, some of them get absorbed.

  • Objects with lower density, like stuff that's made of organic materials, will allow more

  • of the lower-energy X-rays to pass through.

  • And things with higher density will absorb most of the low-energy X-rays, and allow some

  • of the higher-energy rays to pass through.

  • Based on the X-rays that reach the detector, the machine generates an image that shows

  • all the different objects in your bag, colored based on their density.

  • If something is colored orange, for example, that means it's probably made of organic

  • materialthat is, something that contains carbon.

  • That's important for security to know, because explosives tend to involve organic compounds.

  • The security team analyzes the image for anything suspicious, like the outline of a gun or a

  • bunch of organic material hidden inside a shoe.

  • With all those X-rays scanning thousands of bags every day, you might think that security

  • personnel would be exposed to a lot of radiation.

  • But the X-rays are confined to the machine, so the amount of radiation that workers are

  • exposed to is so low that they aren't even required to wear badges that monitor radiation exposure.

  • While your bag goes through the X-ray machine, you've probably been asked to step through

  • some kind of scanner yourself.

  • Until a few years ago, that scanner was usually a metal detector.

  • Metal detectors work by generating a current in a coil of wire in short pulses, each of

  • which briefly creates a magnetic field within the detector.

  • When a metal object passes through the detector, this magnetic field creates another current

  • in the metal, which in turn generates another magnetic field around the object.

  • The interference caused by this magnetic field is what sounds the alarm.

  • But these days, you're probably not asked to step through a metal detector.

  • Instead, you walk into some big machine and raise your hands.

  • This machine is either a backscatter X-ray or millimeter wave scanner.

  • If the machine just looks like a flat wall, it's probably a backscatter X-ray scanner.

  • These use very small amounts of weak X-rays that only penetrate your clothes, and don't

  • go through your skin.

  • The machine detects the radiation reflected by your skin and anything else under your

  • clothes, and generates an image that easily shows anything you're trying to conceal.

  • The amount of X-ray radiation you're exposed to in a backscatter scan is extremely low,

  • a tiny fraction of the amount you're about to be exposed to by flying on a plane.

  • But still, this technology isn't used very often, and it's banned in many countries.

  • Instead, millimeter wave scanners are much more common.

  • They're the cylindrical machines that look like futuristic phone booths, and they use

  • the same basic principles as backscatter scanners.

  • But instead of X-rays, they emit microwaves, which are non-ionizing, meaning that they

  • can't damage your DNA, and you don't need to worry about exposure.

  • Since millimeter waves can penetrate through clothing, they can still show if you're

  • hiding something that you shouldn't be.

  • Once you make it through the scanner though, you might still be in for some follow-up tests.

  • If security finds anything in your bag that looks suspicious, they'll probably

  • swab you for traces of explosives.

  • A security officer might swab your hands, your shoes, or your bag, then place the swab

  • in yet another machine for analysis.

  • This is the Explosives Trace Detection machine, or ETD.

  • The idea here is that, if you've been handling explosives, or if there were any inside your

  • bag, the swab will pick up traces of suspicious compounds.

  • To analyze the swab, the ETD uses a process called ion mobility spectrometry.

  • The machine gives the molecules on the swab an electric charge, turning them into ions.

  • Then, a gas carries the ions through a tube.

  • Different ions will take different amounts of time to pass through the tube, depending

  • on things like their mass and charge.

  • The machine then identifies different compounds based on how long it took them to move through

  • the tube.

  • So, airport security might be tedious and annoying.

  • But at least now you know what's happening to you and your carry-on.

  • Thanks for watching this episode of SciShow, which was brought to you by our patrons on Patreon.

  • If you want to help support this show, just go to

  • And don't forget to go to and subscribe!

Airport security is the most awkward, confusing, and tedious part of every trip!


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B1 中級 美國腔

机场安全科学(The Science of Airport Security)

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    joey joey 發佈於 2021 年 07 月 02 日