Rads on a Plane

by Dr. Tony Phillips (This article originally appeared on Spaceweather.com)

05 Nov. 2015: Spaceweather.com and the students of Earth to Sky Calculus regularly fly helium balloons to the stratosphere to measure cosmic rays. For the past six months, May through Oct. 2015, they have been taking their radiation sensors onboard commercial airplanes, too. The chart below summarizes their measurements on 18 different airplanes flying back and forth across the continental United States.

The points on the graph indicate the dose rate of cosmic rays inside the airplanes compared to sea level. For instance, the dose rate for flights that cruised at 40,000+ feet was more than 50 times higher than the dose rate on the ground below. No wonder the International Commission on Radiological Protection (ICRP) classifies pilots as occupational radiation workers.

Cosmic rays come from deep space. They are high energy particles accelerated toward Earth by distant explosions such as supernovas and colliding neutron stars. Astronauts aren’t the only ones who have to think about them; flyers do, too. Cosmic rays penetrate deep inside Earth’s atmosphere where airplanes travel every day.

Our radiation sensors detect X-rays and gamma-rays in the energy range 10 keV to 20 MeV. These energies span the range of medical X-ray machines and airport security scanners.

Cosmic Rays are modulated by solar activity. Solar storms and CMEs tend to sweep aside cosmic rays, making it more difficult for cosmic rays to reach Earth. Low solar activity, on the other hand, allows an extra dose of cosmic rays to reach our planet. This is important because forecasters expect solar activity to drop sharply in the years ahead as we approach a new Solar Minimum. Cosmic rays are poised to increase accordingly.

The plot, above, tells us what is “normal” in 2015. How will it change as the solar cycle wanes? Stay tuned for regular updates.