If I were in America, the TSA agent would have called in backup on the spot and I would have received a long questioning. I had just asked the airport security agent if I could leave my laptop open as it rolled through the x-ray scanner. I pointed to the black thumb drive-looking thing sticking out of my USB port. I told them all I wanted to do was test the radiation levels using the attachment, the MiniPix USB particle camera.
This wasn’t the US, this was the Geneva airport, which shares its borders with the Large Hadron Collider, the world’s largest particle accelerator. Some physicists have literally booked seats for parts of their experiments, so it’s unlikely that my request was the strangest. “Okay,” the security agent said in her Swiss-French accent, “I always wondered how much radiation I got standing here all day.”
The MiniPix is a plug-and-play Geiger counter for your laptop. But rather than clicking like a Geiger counter, it takes pictures of the radiation that passes through its 256 by 256-pixel TimePix detector. It’s teeny and deceptively simple to use, but if you’re in space, you’ve just survived a nuclear apocalypse, or you’re a physics fan interested in how much radiation hits you on a daily basis, it’s about as fun as a product can get. If you’re not a physicist, you don’t need a four thousand dollar radiation camera like the MiniPix—but once you’ve got it, you’ll leave it on waiting for the highest-energy cosmic rays to blast it, or you’ll put a banana on top of it, or maybe even hunt for the most radioactive place in your city.
That’s what we eventually did. But before going out into the field, I had to figure out how the MiniPix device and its TimePix chip actually work.
The Minipix device detects ionizing radiation particles, the kinds of particles which knock electrons off of the atoms in the sensor. These electrons migrate into the electronics, which decide whether the hit was high enough energy to become a signal indicating a particle or if it was just random electrons causing noise.
You might remember some of the different kinds of ionizing radiation from school, but we’ll go over the ones you’ve heard of (and some other ones) real quick.
Ionizing radiation can come from radioactive elements like uranium decaying, it can be produced in high-energy particle physics experiments, or it can strike the Earth from space. Alpha particles are two protons and two neutrons stuck together. Some elements lose alpha particles through radioactive decay, and your smoke detectors use them to detect smoke. They’re mainly harmful if you inhale or ingest them, since skin can stop them, according to the International Atomic Energy Agency. Radioactive materials can also release beta particles, another name for electrons and their antimatter partner, positrons. These are more dangerous and can penetrate deeper into skin. Massless gamma rays consist of high energy light and requires layers of concrete to stop. In higher concentrations they can even cause cancer.
Cosmic rays can include even wilder particles, like entire atomic nuclei, muons (which are kind of like heavier electrons) and other heavier particles. Those particles are even cooler—they could come from the strangest events in the universe, like exploding stars.
The MiniPix can, theoretically, photograph all of these particles as they pass through the sensor. Its How-To guide would likely prove impenetrable for a non-physicist (I asked a physicist for help), but the setup is simple: it comes with another USB stick loaded with the Pixet software, whose installation is a painless process on any non-ancient Windows, Mac or Debian/Ubuntu Linux machine. On opening, you can change the image settings to make the particle tracks look prettier or assign colors to different energies that show up on the chip. You either set it to Frames or Integral, meaning either clear the frames after a given time range or sum them all up. Frames can give you a snapshot of the radiation of a short period of time, while integral can give you an overall view of the radiation for longer periods.
Then just hit the Start button.
After making it through security and learning that, yes, there were x-rays (but they’re shielded and not especially high-energy), I boarded the plane, which was a good start to really measuring ionizing radiation. Flying six miles up, travelers are exposed to the equivalent radiation of eight dental x-ray exams thanks to the cosmic rays, according to NPR.
Alphas showed up as big splotches, betas as long curls a single pixel wide, muons as straight lines, and high energy light like gamma rays as single pixels. Heavier particles can leave some crazy-looking tracks and blobs. Fifteen minutes left a concerning image of what the human body is subject to every time it hits 30,000 feet.
When I got home, I spent a few nights testing the chip with radiation from some everyday items like bananas and an old smoke detector: The banana didn’t leave a noticeable signal, but the radioactive americium source in the smoke detector produced a shower of alpha particles. Once I got the hang of it, I googled the most radioactive spot in New York City, the site of the old Wolff-Alport Chemical Company, now an auto repair garage and an EPA superfund site.
If I was going to really test the chip scientifically, I’d need a control and experimental trial. I went to the Mount Carmel cemetery next door and ran the chip for twenty minutes in the shade, picking up just some stray cosmic rays.
No one at the auto repair shop nor the store next door minded my coming in to test the radiation, since the EPA had only recently visited to install some shielding on the ground. And after another twenty minutes, the reading was clear: there was way more radiation here than at the cemetery only a few blocks away.
There are definitely some drawbacks to a pocket full of radiation detection. That’s to be expected for any piece of physics equipment that a dummy like me literally just asked a physicist if I could borrow. It runs pretty hot. You shouldn’t run it in the sun (why did I do that) because it will pick up the more energetic light and almost every pixel will record a hit. And if you’re testing it with a banana, make sure you put a piece of Saran wrap over the detector since it’s incredibly sensitive (CERN: I did not get any banana on your chip). You’ll also need some sort of analysis package to analyze your data in a meaningful way. And it costs four thousand bucks.
People actually use this chip for things other than screwing around, by the way. NASA uses the MiniPix to monitor radiation on board the International Space Station. And the team developing the chip offers a wide array of these kinds of radiation cameras for experiments. Some of the experiments at CERN will soon use TimePix chips to look at the particle decays, or the background radiation that they need to understand to better see the things that they’re looking for.
CERN physicist Michael Campbell who lent me the chip told me there were even more potential uses I didn’t try out: Punch a few pinholes through a sheet of foil in front of the chip and you’ve got a camera obscura, which you can use to capture the image all of the gamma radiation in a room, say, after a nuclear meltdown.
As useful as this might seem, it’s unlikely you’ll need it unless you live near a superfund site, are a physicist, or are trying to escape from Chernobyl. It’s the best (only) pocket-sized particle detector I’ve ever used. It’s cool to carry something like it with you, knowing that some people way smarter than you are are doing more important things than putting a banana onto it and stumbling around a neighborhood on the border of Brooklyn and Queens.
- A super-advanced and easy-to-use particle detector that you can also fit in your pocket
- Intuitive software requires minimal customization
- Literally a piece of lab equipment I borrowed from CERN
- Do not leave your laptop unattended at an EPA superfund site next to a cemetery
The reporting for this article was partially supported by a grant from the National Science Foundation
Video produced by Eleanor Fye and shot by Carmen Hilbert.