Neutron Radiation over the USA

April 17, 2019: Want to experience space weather? Just step onboard an airplane. At typical cruising altitudes, cosmic rays from deep space penetrate the hulls of commercial jetliners, dosing passengers with levels of radiation comparable to dental X-rays. To measure this radiation, Spaceweather.com and the students of Earth to Sky Calculus have been flying cosmic ray sensors onboard airplanes over 5 continents. Our latest results show something potentially interesting about the continental USA.


Above: Neutrons detected during a flight from Portland to DC on April 9,2019.

On April 9th and 11th we flew neutron bubble chambers from Portland, Oregon, to Washington DC and back again. In the photo, above, each bubble was created by a cosmic ray neutron. Why measure neutrons? Studies show that neutrons can be ten times more effective at causing biological damage compared to X-rays and gamma-rays in the same energy range. Neutrons are so effective, they are used for cancer therapy, killing tumors better than other forms of radiation.

During these flights, we measured more than 20 uGy of neutron radiation–the whole body equivalent of two panoramic dental X-rays. That’s significant, but no worse than a trip to the dentist’s office.

The interesting thing is how these values compare to other places we’ve flown. Our neutron chambers have traveled more than 40,000 miles on 14 flights over North America, South America, Asia, Europe, and Africa, all with typical altitudes near 35,000 feet. So far, neutron dose rates have been highest in one place: the continental USA (CONUS).

In this histogram, flights over CONUS are color-coded red. Other parts of the world are blue. The distribution’s red tail shows the tendency of US flights to “out-neutron” international flights. This may be a result of small-number statistics. If so, the anomaly could disappear as more data are added. Our neutron survey is continuing, so stay tuned.

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