Cosmic Rays GNEP Teacher Workshop Steve Shropshire, July 2007

2 Outline What Are They? Why Bring Up Cosmic Rays in High School Physics? Where Do They Come From?

3 Cosmic Rays Relativistic particles from space, primary cosmic rays –Protons, Alpha particles, Electrons, Gamma rays, Heavy nuclei (Fe, Ni, etc.) Only gamma rays are traceable to their source Until recently, no evidence existed indicating their origin – many theories

4 Origin: Long-Standing Puzzle First discovered in 1912 – Viktor Hess –Early high-altitude balloon flights –Cosmic rays strike the atmosphere and generate big showers of elementary particles –Some have HUGE energies

5 Cosmic Ray Showers Mostly neutrinos and muons reach the surface of Earth

6 What makes a shower? Primary cosmic rays interact with nuclei of atoms in the atmosphere to produce new, often unstable particles called secondary cosmic rays such as pions and kaons Secondary cosmic rays decay and create muons, electrons, photons, and neutrinos If secondary cosmic rays are sufficiently energetic, they can reach the earth's surface and be detected. (Neutrinos are capable of passing through the earth and are generally undetected.)

7 Muons: solid red lines Neutrinos: dashed red lines

8 Why Bring Up Cosmic Rays in High School Physics? Great introduction to lots of really cool physics –Particle physics, astrophysics, cosmology Excellent example of natural radiation –Significant contribution to background radiation dose –Useful for reducing radiation phobias

9 Origin of Cosmic Rays Our sun and other stars (10 4 to 10 5 eV) Neutron stars (up to 10 4 eV) Supernovae (up to eV) Big Bang Relic Neutrinos – huge flux Above eV? Current theories: –Pulsar and black hole jets –Stellar and galactic collisions –Black hole accretion disks –Black hole mergers –…………

: First Direct Evidence CR Origin Southern Hemisphere –Radio image –X-ray contours –2 times angular size of the moon Supernova shock wave

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12 NGC4260

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