Rads on a Plane, Continued

Rads on a Plane, Continued

Many people think you have to go all the way to the Arctic Circle to experience space weather. Not so. All you have to do is board an airplane. Every day more than 8 million people fly somewhere on Earth. All of them are exposed to cosmic rays, a form of high-energy space radiation. To illustrate the point, yesterday Dr. Tony Phillips of spaceweather.com carried a pair of ionizing radiation detectors onboard a US Airways flight from Reno to Phoenix. At cruising altitude (38,700 ft) he measured dose rates 42 times higher than at ground level:

At this rate, a passenger flying for 5 hours could be exposed to about as much radiation as a dental X-ray--not dangerous, but not negligible either.
The radiation comes from space. Cosmic rays are subatomic particles accelerated to nearly light speed by supernovas, active galactic nuclei, and solar flares. Earth is peppered with this kind of radiation, every day, from all directions. Cosmic rays penetrate our planet's atmosphere, producing a spray of secondary particles that air travelers routinely (and mostly unknowingly) absorb as they fly.
Cosmic rays are a genuine form of space weather. They fluctuate in response to solar storms--both up and down. For example, solar flares can accelerate energetic particles toward Earth, adding to the flux of cosmic rays. CMEs, on the other hand, sweep aside cosmic rays, causing radiation counts to dip. When you step on a plane, you're never quite sure what you're going to get.
Case in point: Phillips took the same flight from Reno to Phoenix on Nov. 11, 2014. He measured 40% more radiation then vs. now. The difference is not fully understood.
Here are the data from yesterday's flight:

The two curves, orange and blue, trace data from two identical yet independent radiation detectors. Differences between the two curves are an indication of the measurement uncertainty. Using helium balloons, spaceweather.com and the students of Earth to Sky Calculus have flown these detectors to the stratosphere dozens of times to monitor the response of Earth's upper atmosphere to solar storms. They are sensitive to ionizing radiation such as X-rays and gamma-rays in the energy range 10 keV to 20 MeV.
It is important to note that these sensors sample only a fraction of the total radiation. In particular, they are not sensitive to neutrons, a key form of biologically effective radiation at aviation altitudes. Adding neutrons to the count could more than double the measured dose.
Later today, Phillips will fly back from Phoenix to Reno. What will he measure then? Stay tuned!

From SpaceWeather.com