Are cosmic rays of any use, are they a danger?

Cosmic rays are of undoubted interest to scientists as direct messengers of extremely high-energy
astrophysical processes and witnesses of the distribution of galactic magnetic fields and the interstellar medium, whose models must be reproduced by observations.

Cosmic-ray research is still, after nearly a hundred years, an active field with many unresolved questions. Thus, for example, while it is possible that supernova remnants may be the sites where galactic cosmic rays of energies up to 1015 eV are accelerated, this does not seem to be the case for higher energies. For these, for the time being, there are no solid and established models that account for all that has been discovered.

Although almost all known mechanisms or scenarios capable of generating the necessary energies have been proposed, such as jets from supermassive black holes at the centre of active galaxies, other exotic processes -that we’re not able to even imagine now- cannot be ruled out.

But cosmic rays do not only pose problems for "fundamental" physics, but are also relevant to many other problems closer to what our everyday life is or could be in the future (1).

To begin with, we think that there is only one thing more impressive than seeing cosmic ray traces in a fog chamber: "seeing" with closed eyes the flashes that many astronauts have seen on their space voyages and which probably have the same origin. But if you are an astronaut, there are more serious consequences of cosmic rays which, like other ionising radiation, are capable of producing changes in DNA or other biomolecules, as well as computer glitches.

On the Earth's surface we are largely shielded by the Earth's magnetic field and atmosphere - and by the "solar wind" - but even so this radiation contributes to the natural radioactive background that has always produced mutations, probably contributing to natural selection. When boarding an aeroplane and flying at an altitude of about 10 km, cosmic radiation levels increase about 20 times, which could constitute an occupational hazard for crews. Finally, a few km above where the planes fly, neutrons from cosmic rays convert a small fraction of nitrogen into radioactive carbon-14 that can be used to date biological samples.

In addition, cosmic rays reaching the Earth are already a business opportunity; there are companies - such as Muon Systems - that use detectors like those developed for research to make "muongraphs", i.e. density maps of an object similar to X-rays - because the higher the density of a medium, the more of the constant flux of cosmic rays it absorbs, just like X-rays. These techniques have been used to study large structures such as pyramids - in which unknown chambers have been found - but also to analyse caves, blast furnaces, containers, etc.

Finally, cosmic rays could be related to cloud formation due to the possibility that the ions, which are created by the particles as they pass through the atmosphere, serve as condensation nuclei around which clouds form, so this mechanism could have some impact on the Earth's global climate.

_{(1) More information about elementary particles at https://particleadventure.org/ or, only in Spanish, in the Experimenta booklet “Cosmic rays”: http://www.muncyt.es/stfls/MUNCYT/Publicaciones/rayos_cosmicos_muncyt.pdf}