COSMIC%20RAYS

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COSMIC RAYS

• An Overview

Dr. Darrel Smith Department of Physics Embry-Riddl
e Aeronautical University Prescott, AZ 86301
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Cosmic rays-early beginnings

• C.T.R Wilson discovered in 1900
• the Earths atmosphere was continually ionized.
  
• It was believed to be due to the natural
  radiation from the Earth. In other words, from
  the ground up.
• Wilson noticed the reappearance of drops of
  condensation in expanded dust free gas, the first
  cloud chamber.

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The Wilson Cloud Chamber
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Where did the ions come from?

• At the beginning of the 20th century, scientists
  were puzzled by the fact that more radiation
  existed in the environment than could be
  explained by natural background radiation.
• The debate was resolved as a result of a balloon
  flight in 1912 from the University of Vienna.

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Victor Hess

• In 1912 a Victor Hess, a German scientist, took a
  radiation counter (a simple gold leaf
  electroscope) on a balloon flight.
• He rose to 17,500 feet (without oxygen) and
  measured the amount of radiation as a function of
  altitude.

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Victor Hess and the Balloon

• Victor discovered that up to about 700 m the
  ionization rate decreased but then increased with
  altitude.
• This showed that outer space was the source of
  the ionization.

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Not from the Sun

• During subsequent flights Hess determined that
  the ionizing radiation was not of solar origin
  since it was similar for day and night.
• It was initially believed that the radiation
  consisted of gamma rays only.
• But there was still a dispute as to whether the
  radiation was coming from above or from below.

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Source of Cosmic Rays

• In 1925 Robert Millikan of Caltech introduced the
  term cosmic rays after concluding that the
  particles came from above not below a cloud
  chamber.
• He used elaborate electroscopes.

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Extensive Air Showers

• Cosmic rays enter the earths upper atmosphere
  and interact with nuclei.
• Secondary particles result that also interact.
• The shower grows with time.

• Some particles never reach the surface.
• Some particles, such as muons, do reach the
  surface and can be detected.

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The Spark Chamber

• In the 1960s, spark chambers were common. When
  a charged particle ionizes gas between the
  plates, sparks fly along the track, marking the
  track of the particle.

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Composition of Cosmic Rays

• Primaries are particles with energies from 109
  eV to 1021 eV.
• An eV is a unit of energy. A 40 W reading light
  uses about 1034 eV of energy in one hour.
• (from James Pinfoli,
• Pinfold_at_phys.ualberta.ca)

• Cosmic rays within therange of 1012 eV to 1015
  eV have been determined to be
• 50 protons
• 25 alpha particles
• 13 C, N, and O nuclei
• lt1 electrons
• lt0.1 gammas

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Cosmic Ray Energies

• Existing models for the production of cosmic rays
  only work to 1015 eV.
• CR in excess of 1019 eV are believed to come from
  sources relatively close to our Galaxy, but the
  sources are unknown.
• The highest energies!
• (from,www.phys.
• washington.edu)

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Present Cosmic Ray Studies

• Cosmic Ray studies continue in spite of the
  development of high energy particle accelerators
  1012 eV.
• The energy of the highest energy cosmic rays
  still cannot be duplicated in accelerators.

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Fermilab Modern-Day Accelerator
E 1012 eV
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Where do cosmic rays come from?

• Low energy rays (less than 10 GeV) come from the
  sun.
• Supernovae may be the source of particles up to
  1015 eV.
• The sources for ultrahigh cosmic rays are
  probably, active galactic nuclei and gamma ray
  bursts.
• (www.phys.washington.edu)

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Supernovas

• Nuclei receive energy from the shock wave of the
  supernova explosion.
• The energy spectrum indicates that most of the
  supernova particles have less than 1015 eV
• (image fromwww.drjoshuadavidstone.com/
  astro/supernova.jpg

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High School Based Detectors

• Numerous CR detector arrays have been built and
  are located at high schools.
• The projects range from
• arrays using hundreds of detectors covering
  thousands of km2 to
• small arrays involving only a few detectors in an
  area only a few hundred meters square.

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CHICOS (California high school cosmic ray
observatory)

• Operated by Caltech, CHICOS is an active research
  array with a goal to study CR is the range of
  1018 to 1021 eV using refurbished detectors from
  a neutrino experiment and 1 m2 scintillators
• Currently 51 sites are setup and working.
• Image from www.chicos.caltech.edu

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ALTA (University of Alberta Large Time
Coincidence Array)

• The stated purpose of the ALTA project is to
  search for time correlations between EASs.
• At present 16 high schools are involved.
• The project is part of the Canadian learning
  standards with students receiving credit.
• (image from www.physics.ubs.ca)

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ALTA MAP
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CROP (Cosmic Ray Observatory Project, University
of Nebraska)

• A project to study EAS from particles gt 1018 eV.
• Thirty operating schools covering 75,000 sq miles
  is the goal of the project.
• Detectors are 1 m2 scintillators donated by the
  Chicago Air Shower Array.
• Image from Marion High School. Http//marian.creig
  hton. edu

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SALTA (Snowmass Area Large-scale
Time-coincidence Array)

• A project to set up detectors in Colorado.
• Linking high schools via Internet connecting to
  form a large array.
• A modern hot-air balloon flight in 2001 reenacted
  Hesss 1912 flight. Image from
  http//faculty.washington.edu/wilkes

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WALTA (Washington Large Area Time Array)

• A project of the University of Washington.
• As of late 2002 eighteen high schools around
  Seattle are participating. See image. (from
  www.phys.washington.edu )

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The Pitt/UMSL Projects

• A project of the University of Pitt and
  University of Mo at St. Louis.
• The project involves high school teachers
  building and using scintillator type detectors
  aimed at muon detection.