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Slide 1 - Hall A - Jefferson Lab

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					      Cosmic ray activity




                                                                                                                                                     Simulation of a proton hitting the atmosphere
                                                                                                                                                      about 20km above the ground. The cosmic
                                                                                                                                                      shower is superimposed on a scale map of
                                                                                                                                                     Chicago's lakefront. Electrons & positrons are
                                                                                                                                                      green, muons are red, and gamma rays are
                                                                            Cosmic ray air shower with telescope                                                        yellow.
                                                                                     ground detection


                                             Since the 20th century, scientists have been fascinated by the phenomena of excess radiation in
                                             the environment, other than by the known sources of natural background radioactivity. Scientists
                                             have found that cosmic rays bombard the Earth, at different rates, dependent upon their energy.
                                             Cosmic rays surround us. They make up about half of the natural background radiation of our
                                             planet. These rays are ionized atoms that originate from space. Traveling very close to the speed
                                             of light, they are produced by a number of different sources such as the sun, other stars, black
                                             holes, neutron stars, supernovas and their remnants. Our focus is to design and construct a
                                             scintillator detector. This device will count the particles passing by, by showing light and emitting                                                         Valerie Bicouvaris
                                             sound. It will be made from a type of plastic called, scintillator. When fast moving, charged                                                               Berkeley Middle School
                                                                                                                                                                                                           Williamsburg, VA
                                             particles, such as cosmic rays pass through the scintillator, they excite the atoms in the plastic by
            Cosmic ray detector              giving them some energy. The cosmic ray slows down, and the excited atoms then lose this                                                                 Douglas W. Higinbotham, Ph.D.
        (construction in progress)           energy by emitting some photons of light. This light is detected by a piece of equipment called a                                                              Thomas Jefferson
  Components include: fan in fan out/                                                                                                                                                                  National Accelerator Facility
                                             photomultiplier. The photomultiplier multiplies the small flash of light into a large electrical
 discriminator, logic unit, counter, PMT     signal that can be measured. The size of the electrical signal determines how many particles
       (2), and scintillator paddles,        passed through the scintillator. Both the scintillator and photomultiplier are housed in a dark box                                                           Special Thanks to:
                                                                                                                                                                                                         Douglas W. Higinbotham
   which together, detect and count the      so that the only light detected is caused by cosmic rays. This spark chamber device will be                                                                       Jack Segal
                  photons                    portable and will be used to demonstrate to visitors to Jefferson Lab, as well as students, teachers,                                                             Lisa Surles
   being ‘knocked off’ the scintillator      etc., how cosmic rays are everywhere, and how they pass through our atmosphere where they
                                                                                                                                                                                                              Dave Abbott
                                                                                                                                                                                                            Delisa Smith-Bell
and pass through the photomultiplier tube.   collide with molecules, and rain down millions of highly-charged particles on the Earth's surface                                                                 Bill Vulcan
                                                                                                                                                                                                               Gary Hays
                                             every second.

				
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posted:8/11/2012
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