Cosmic Ray Origins Still A Mystery
August 1, 2012

Cosmic Ray Origins Still A Mystery 100 Years Later

April Flowers for - Your Universe Online

In August, physicists will gather to celebrate a century of research since the discovery of cosmic rays. It is widely accepted that cosmic rays are the nuclei of atoms, from the full array of naturally occurring elements that travel at near-light-speeds for millions of years before reaching Earth. What isn't known yet is where these cosmic rays originate.

Alan Watson, emeritus professor of physics at the University of Leeds, provides an overview of a century's work to explain this phenomenon and examines the progress being made in August's edition of Physics World.

In the 1780's French physicist Charles-Augustin de Coulomb noticed that an electrically charged sphere spontaneously lost its charge.  At the time, scientists believed air was an insulator, not a conductor, so this was very strange. Investigation showed that air becomes a conductor when charged particles or X-rays ionize the molecules. The source of these charged particles confused the scientists of the day as experiments revealed that objects were losing their charge even when blocked by large volumes of lead, which was known to block X-rays and radioactive sources.

On August 17, 1912 an Austrian scientist, Victor Hess, discovered the source of this ionization while traveling 5,000 meters above the ground in a hot-air balloon.  Hess found that the ionization of air molecules was three times greater at high altitudes than it was at ground level. This led him to conclude that the source of the radiation was penetrating our atmosphere from above. Hess was awarded the Nobel Prize for Physics in 1936 for his work.

Research has come a long way from charged spheres and hot-air balloons. The Pierre Auger Observatory in Argentina, with a 3,000 square kilometer campus, is one of many facilities around the world trying to find the origin of these cosmic rays. The Observatory currently has 1,600 Cherenkov detectors; particle detectors that allow discrimination between radiating and non-radiating particles, each looking to find the source of cosmic ray showers with extremely high energy.

Watson states that there have been unexpected benefits coming from Hess' original investigations into cosmic rays. The designer of the communications system at the Pierre Auger Observatory uses the same software to build a radio-based signaling system. This system extends over 700 kilometers of the single-track train line in the Scottish Highlands.

“The safety and reliability that rail travelers now enjoy while passing by lochs and through glens is a benefit from Hess´s daring flight a century ago that surely he could never have foreseen,” Watson writes.