|Evening Public Lecture (8:00 PM on Monday, April
"COSMIC RAYS: A FASCINATING SCIENTIFIC HISTORY"
In 1912 it was discovered that radiation arrived on earth from outer space. The story of this discovery is linked with adventure, false starts and scientific rivalry. We will present some vignettes from this story. For years, a controversy raged as to what was the nature of this radiation -- charged or neutral particles. A prominent discovery was made by the French physicist Pierre Auger in Paris in 1938. He found among this radiation particles with energies more than eight orders of magnitude greater than any natural or artificially produced radiation native to our earth. The energy of the cosmic rays observed by Auger was about 1015 eV -- a macroscopic energy in a microscopic particle. In 1963, a cosmic ray was discovered with an energy of 1020 eV, an energy of 16 joules. To understand how nature produces these highest energy cosmic rays has been my passion and the inspiration for a large observatory in Argentina in an attempt to solve the mystery. In the Physics Colloquium tomorrow I will describe the observatory and some of the early results. I invite all of you to attend. The lecture is a bit more technical, but I believe it is quite comprehensible because of the simplicity of the detection principles.
|Colloquium: Tuesday, April 4, 2006:
James W. Cronin, The University of Chicago
"The Pierre Auger Observatory for Highest Energy Cosmic Rays"
The existence of cosmic rays with energies in excess of 1020 eV represents a scientific mystery whose solution can be found, if at all, only by experimentation. I will describe the Pierre Auger Observatory, now nearing completion in Malargue, Mendoza Province, Argentina. The observatory detects showers of particles produced by high energy cosmic rays (protons, nuclei, perhaps photons and neutrinos). Showers produced by cosmic rays of 1020 eV produce about 1011 particles spread over 50 km2 on the ground. Two techniques are employed to observe the showers: detection of the shower particles on the ground and detection of fluorescence light produced as the shower particles pass through the atmosphere. The observatory is spread over 3000 km2 as the fluxes of the most energetic cosmic rays are very small, roughly one/km2/century above an energy of 1020 eV. I will describe the design principles and construction of the observatory and early results from the observatory, which has recorded data even while partially complete.
Hofstadter, winner of the 1961
Nobel Prize, was one of the principal scientists who
developed the Compton Observatory.
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