Cosmic RaysCosmic Rays

GNEP Teacher WorkshopGNEP Teacher Workshop

Steve Shropshire, July 2007Steve Shropshire, July 2007

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OutlineOutline

• What Are They?

• Why Bring Up Cosmic Rays in High School Physics?

• Where Do They Come From?

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Cosmic RaysCosmic 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

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Origin: Long-Standing PuzzleOrigin: 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

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Cosmic Ray ShowersCosmic Ray Showers

Mostly neutrinos and muons reach the surface of Earth

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What makes a shower?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.)

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Muons: solid red lines

Neutrinos: dashed red lines

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Why Bring Up Cosmic Rays in High Why Bring Up Cosmic Rays in High School Physics?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

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Origin of Cosmic RaysOrigin of Cosmic Rays

• Our sun and other stars (104 to 105 eV)• Neutron stars (up to 104 eV)• Supernovae (up to 1014 eV)• Big Bang Relic Neutrinos – huge flux• Above 1014 eV? Current theories:

– Pulsar and black hole jets– Stellar and galactic collisions– Black hole accretion disks– Black hole mergers– …………

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2004: First Direct Evidence CR Origin2004: 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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1212NGC4260

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