Quickly Prototyping X-ray Backscatter Machines

Ben Krasnow is one of those people no one has a bad opinion of. He’s part of the team at Verily (Google’s Life Science Alphabit), where he’s busy curing cancer. He co-founded Valve’s hardware division and his YouTube channel, Applied Science, is an exploration of building very high-tech tools very quickly and on a very low budget. Ben has built everything from an electron microscope to a liquid nitrogen generator to a robot that makes individual chocolate chip cookies with ingredients in different proportions. He’s curing cancer and finding the perfect chocolate chip cookie recipe.

The focus of Ben’s talk at this year’s Hackaday SuperConference is building low-cost scientific apparatus quickly. From Applied Science, Ben has cemented his position as a wizard who can find anything either on eBay or at a surplus store. The real trick, Ben tells us, is getting his boss and accounting to understand this rapid prototyping mindset.

The first build Ben walked the SuperCon through was a device to test a hypothesis. Were X-ray backscatter machines, the devices found at airport security lines from about 2009 to 2013, actually effective at stopping terrorists? Although there are obvious safety and civil liberties questions raised by assessing X-ray backscatter devices, this is simply a question on the effectiveness of the TSA’s fanciest new gear. Do X-ray backscatter devices stop terrorists more effectively than a metal detector?

A chicken, wearing a sweater, and smuggling an allen key onto its flight. Chickens can fly.
A chicken, wearing a sweater, and smuggling an Allen key onto its flight. Chickens can fly.

The answer to this question came in a one-month build. Even at the beginning of the build, Ben says he didn’t know much about X-rays. Backscatter X-ray machines aren’t like what you would find at a dentist’s office – those are transmissive X-rays, and giving millions of flyers X-rays every day would be a worldwide health crisis.

Instead of shooting X-rays through everyone who goes through a TSA checkpoint, backscatter X-rays operate on an entirely different principle. After a quick patent search, Ben found a very good description of what backscatter X-ray scanners do, and began work on constructing a prototype to assess the effectiveness of these devices.

The build consisted of an X-ray source easily found on eBay, a phosphor screen found on eBay, a photomultiplier tube found on eBay, and a few bits and bobs kicking around the junk bin in the shop. Although you can simply buy a Rapiscan Backscatter machine (taken from an airport on eBay), that would cost several thousand dollars. Ben only spent a few hundred on his machine.

After building a device to scan an object with X-rays and detect the reflected photons, Ben had a working backscatter X-ray machine. It successfully detected an Allen key being smuggled by a chicken onto a plane. It’s a simple setup, but it proves you can make very complex devices very easily using parts bought on eBay.

The take away from Ben’s talk is simply rapid prototyping. Iterate often, find all the information that’s readily available online, and build prototypes quickly. Leverage the availability of everything being for sale somewhere. Build first, and ask questions later, and you might have the time to discover the perfect cookie recipe.

15 thoughts on “Quickly Prototyping X-ray Backscatter Machines

  1. Most backscatter machines you come across in airports are mm wave backscatter machines. I don’t think I’ve seen a x-ray version in any airport I’ve been through in the US anyway.

    1. Both X-rays and mm-waves are not detectable with human senses, so you can’t be categoric about what you’ve seen. AFAIK millimetre wave scanner couldn’t detect Allen key *inside* chicken, it could only detect one hidden under chicken’s pullover. X-rays are used on road border passes now, they find all hidden spaces in vehicles. Health concern? Stay at home, until they deploy city block scanner big rig patrols!

  2. So, for someone who works at Google…the difference between a hundred dollars and a thousand is maybe a few hours of time for the company after overhead, etc (sure, you’re probably salaried, but you could’ve been working on something else)…did it really only take a few hours to source all of those parts, build everything, and risk that your system won’t work as well as a real rapiscan?

    This sort of money saving logic is usually worth it if you’re a hobbyist, but darn, people are expensive when they work for a very high end engineering/CS company, and it really messes with what’s expensive and what’s cheap…

    1. I think the equation is tilted by context. I suspect most of the Thing he is doing is practicing and proselytising rapid prototyping as a methodology, rather than just building a backscatter machine.

    2. I don’t think you are really understanding the concept of R&D….
      Read about Bell labs, from your POV, they were a bunch of geek wasting money. They created IT as you know it today.

      The guy is creating really technical stuff from scrap. It’s highly valuable.
      Plus, reducing the price of something by a factor of 10 never have been a breakthrough?
      Come on, admit that you are trolling.

  3. What does Ben mean: “Build a site that strips the claims out of patients so that anyone can read them without legal implications”. What part is the “Claim” that is different from the rest of the content?

    1. I’m not into legal stuff and don’t know the patent system well enough to answer the question. This is my best guess:
      The claim part of the patent states: The purpose and the restrictions. This means when you read the claim you cannot use the information for a commercial product. When you didn’t read the claim (or never found the claim) you are safe.

      I didn’t know the patent system worked like this. I couldn’t find allot about it. Can someone verify?

      Patents are awesome. Some have great technical detail. You know the ‘magnetic robots’ from a year ago? I found and read the patent. It has much more information in it then the video, also you’ll never have to guess about the principles involved.

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