Radiation while flying

I recently flew interstate for work and decided to do a bit of science on the way. Taking along my handy-dandy geiger counter (which in addition to having a 10yr battery is also blessed by the FCC for flight use), a notebook and a pen, I sketched down the raw counts from the meter every minute of the flight. 

Why did I do this? Well, if you haven't noticed, the universe is trying to kill us. Cosmic radiation comes in from space, but is attenuated from earth's atmosphere. When you start moving outside the earth's atomosphere, the level goes up. Not quite enough to be worrisome, but pretty interesting if you happen to be able to monitor it. 

Science in action. The geiger conter is the yellow device in and the gap at the top shows the GM tube inside. 

It was interesting to force myself to make regular observations every minute. It's just short enough that you don't feel like starting something else, and just long enough that if you're not careful you'll miss your window. There were a few times I missed a minute, or had to jot down a time that was 20 seconds in. Fortunately excel makes it easy to note these times and normalise them back to counts per minute.  

I know it's practically a sin to post a photo of a spreadsheet, but what the hell:
You can see the level that is normal for ground (around 11 counts per minute) spikes up to 350 counts or more when we get up in the air. 

F.A.Q. (or at least expected questions)

  • Aren't you worried about radiation dose? 
    • Short answer? Nope. Long answer? Noooooooooope. Or, the extra radiation I got on my flight isn't a concern with the risk from other things. 
  • What are the units? What exactly does 350 counts _mean_?
    • Going from counts per minute to an actual calibrated unit (like Sieverts) is tricky. Although my counter does that, it's based on certain assumptions about the makeup and energy of the incident radiation. That's why I logged the raw data, so it was easy to see and didn't have any averaging artifacts from the counter's firmware. However when we were at peak altitude and about 350 counts per minute, that was reading about 3.2 uSv/hr. I expereinced this for less than an hour, so pessimistically let's say I got an extra 3.2uSv (micro-Sieverts). For comparison the level on the ground is 0.1uSv/hr and the general public's allowable limit for radiation (over and above normal background) is 1,000uSv per year. 
  • OK, but there'll be some effect, right? 
    • Remotely possible, but it's extremely difficult to determine. If you get a 1,000,000uSv extra dose, then you have a 5% chance of getting cancer in your lifetime from it. For comparison, that means if I'd made about 300,000 flights of the same length, then I'd have had an extra 5% risk of cancer in my lifetime. (To be fair, radiation physics is a tricky subject and doesn't lend itself easily to simple multiplication like that, but at any rate I'm nowhere near a danger zone) 
    • If, on the other hand I was flying every day, then I'd still not exactly be concerned, but I'd be having regular checkups just as a precation. In face pilots and airlines are well aware of this, and have screening. There's even a fact sheet on radiation and flights here
  • So going up in a plane automatically increases your radiation dose?
    • Interestingly enough, no. Go up far enough that there's not enough atomosphere shielding you from space and yes, your radiation level goes up. But, if you go up just a little, so that you're far enough away from the earth that terrestrial radiation isn't a factor, and you still have plenty of atmospheric shielding above you then you can actually see a lesser dose than ground level. 
  • So if you wanted to extend your lifespan could you live on a plane at a low altitude? 
    • Well, if you did then you'd have to content yourself with living in a smal plane (like a Cessna) for the rest of your like in order to achieve a minuscule amount of reduction in risk. Personally, I've never met a plane I liked that much...