Re: cherenkov radiation [ cosmic ray origin ]

["Franta, Jaroslav" <frantaj@aecl.ca>]

Dukelow, James S Jr wrote on Wednesday November 08, 2000 6:04 PM

<snip>
Cherenkov "glow" can occur in air, even dry air, where it is the basis for
an
"instrument", the STACEE (Solar Tower Atmospheric Cherenkov Effect
Experiment),
that uses a heliostat array and a photomultiplier to detect the atmospheric
trace of particle "showers" caused by extremely high-energy gamma rays
arriving
from active galactic nuclei. 
<snip>

Last Sunday serendipity produced a find of an old article that includes some
interesting information on Cerenkov radiation originating from cosmic rays.

Its an article I ripped out of an old issue of Scientific American, called
"The Highest Energy Cosmic Rays" (no date on any of the pages, but its
probably from ~10 to 15 y ago.

The interesting part is where the author talks about these cosmic rays, with
up to 10^19 to10^20 eV energy ("about as much as a very well hit tennis
ball" - and much more that any existing man-made particle accelerators are
capable of...) inducing a mile-wide secondary etc. particle shower along
their trajectory, several kilometers up in the atmosphere (ie. still a
fairly large aspect ratio - with a long, narrow beam path). 
This "disc" of particles, moving at about the speed of light, emits a bright
beam of Cerenkov radiation directly ahead along its path ("like a locomotive
searchlight"). 
This is easy to detect on a clear night, but the camera must be located &
pointing directly in the path of the incoming particles - which at this
extreme energy level is a fairly rare event - perhaps a few per month  ( the
original cosmic ray particle, incidentally, is NOT an extremely high-energy
gamma ray, but is typically an atomic nucleus - of anything from helium to
iron, etc. ).
The article describes several detectors around the world built to track
these rare events, one being the "Fly's Eye" near Salt Lake City, Utah (also
trying to detect a very much fainter fluorescence from these events, which
is emitted omnidirectionally, and therefore more suited to tracking a larger
portion of the events and their point of origin in the sky.)

Presumably there should be an astrophysics web site somewhere on the net
that gives more details on this ?

Jaro
frantaj@aecl.ca

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