[ RadSafe ] 100 years of cosmic rays mystery

[ROY HERREN]

http://www.sciencecodex.com/100_years_of_cosmic_rays_mystery-95837 
100 years of cosmic rays mystery
Posted On: July 31, 2012 - 11:30pm
As physicists gather in early August to celebrate a century since the initial 
discovery of cosmic rays, Alan Watson, emeritus professor of physics at the 
University of Leeds, explains how physicists have gradually revealed the nature 
of these mysterious objects and examines the progress being made in 
understanding where they come from. 

It is now widely accepted that cosmic rays are the nuclei of atoms, from the 
entire range of naturally occurring elements, that travel at near-light-speeds 
for millions of years before reaching Earth. However, identifying the source of 
cosmic rays has proved to be a very difficult task. 

The Pierre Auger Observatory – a 3000 km2 site in Argentina – is one of many 
institutions around the world scouring the universe for the source of cosmic 
rays and currently has 1600 Cherenkov detectors in operation, each looking to 
find the source of cosmic-ray showers with extremely high energies. 

This is in massive contrast to the techniques used by Austrian scientist Victor 
Hess, who was the first to discover cosmic rays on 7 August 1912 by travelling 
5000 m above ground in a hot-air balloon. He was awarded the Nobel Prize for 
Physics in 1936 for his efforts. 

The story of cosmic rays started in the 1780s when French physicist 
Charles-Augustin de Coulomb noticed that an electrically charged sphere 
spontaneously lost its charge, which at the time was strange as scientists 
believed that air was an insulator, rather than a conductor. 

Further investigations showed that air became a conductor when the molecules 
were ionized by charged particles or X-rays. 

The source of these charged particles puzzled scientists as experiments revealed 
that objects were losing their charge even when shielded by a large volume of 
lead, which was known to block X-rays and other radioactive sources. 

Hess was the first to discover that the ionization of air was three times 
greater at high altitudes than it was at ground level, leading him to conclude 
that there was a very large source of radiation penetrating our atmosphere from 
above. 

In this feature, Watson states that there is an unexpected benefit stemming from 
Hess's original cosmic-ray research: the designer of the communications system 
at the Pierre Auger Observatory has used the same sophisticated software to 
build a radio-based signalling system that now extends over 700 km of the 
single-track train line in the Scottish Highlands. 

"The safety and reliability that rail travellers 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. 

Source: Institute of Physics