Radiation is one of the natural phenomena that many people are afraid of: we do not see this mysterious nuclear rays, and rarely do the media talk about radiation without pushing the scare level to the max. But radiation is “natural”: the whole universe, and our planet, and our selves constantly bathe in a continuous flow of charged particles, energetic photons, fast neutrons and mysterious neutrinos which zip through us every second.
1. Cosmic and solar rays
Cosmic galactic rays originate from outside our solar system; they usually interact with nitrogen and oxygen in the atmosphere and produce a shower of different electrons, muons etc. Solar rays represent the “solar wind”, mainly formed from protons which are ejected by the huge solar fusion reactor. The solar wind is more intense when a “magnetic hole” = coronal hole opens at the sun’s surface. The charged protons are than free to be ejected into space; if the hole is directed to the earth, a more or less vigorous stream hits the atmosphere. Such a situation is happening now, as shown by this picture taken from the excellent web-site spaceweather.com (next figures all from this site).
The turquoise circle shows a coronal hole; the white lines and arrows indicated the magnetic field lines which usually trap the protons. The number of these solar protons is continuously monitored by the geo-stationary GOES satellites or the ACE satellite positioned at the Lagrangian L1 point between Earth and Sun. Here the data for today, 15 October 2015:
As you can see, 2.4 protons per cm3 is not negligible: as your body volume is approx. 75 liter ( = 75000 cm3), this means that at this point of observation 180000 protons zip through you every second!
One understands that this type of radiation (and mostly rapid surges) can pose serious problems to astronauts on board of the ISS or future planetary travel.
2. Transatlantic travel by plane
It seems obvious, that cosmic radiation and solar protons are increasing with altitude, as the filtering air layer becomes thinner and thinner. Here is a graph showing the relative increase in radiation dose with altitude. Normal transatlantic flight is at about 40000 feet.
A transatlantic flight would correspond to a 26 times increase.
Now suppose you are a pilot or a steward(ess) and make 10 trips per month, which amounts to about 10*2*8 =160 hours (assuming 8 hours for one flight at high altitude). With a working year of 10 months this would amount to a supplementary radiation dose of 10*160*2200/1000000 = 3.52 mSv/year (the division by 1000000 transforms nSv to mSv). The Health Physics Society gives slightly lower exposures, as for instance 2.19 mSv/y.
Even if the dose rates at high altitudes seem impressive, the supplementary dose from one transatlantic travel is tiny. The usual background dose at many locations on Earth is about 3-4 mSv (with some outliers going up to 260 mSv/y as in Ramsar, Iran), so even pilots and flight crew do not accumulate a dangerous radiation dose. The not so frequent flyer, be it for tourism or business, shouldn’t be scared. But if you intend to spend your next vacation on the Moon or on Mars, things will be different!