COSMIC RAYS

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COSMIC RAYS

• An Overview

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Cosmic rays-a long story

• C.T.R Wilson discovered in 1900 the continuous
  atmospheric ionization. It was believed to be
  due to the natural radiation of 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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Condensation tracks on ions

• Wilson suspected the
• tracks might be condensation on nuclei - ions
  that were the cause of the residue conductivity
  of the atmosphere.

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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 solved on 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 increase as the
  balloon climbed.

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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 showing an outer space origin for
  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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Birth Cries of the Atoms

• 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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Cosmic Ray Electroscope

• Electroscope of cosmic ray apparatus used by
  Millikan. Millikan and a fellow scientist,
  Compton, were locked in a debate about the
  nature of cosmic rays. Compton won, arguing that
  they were charge particles. Millikan believed
  they were uncharged.

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The nature of the raysMuons and Protons

• Seth Nedermeyer and Carl Anderson discover muons
  in cosmic rays.
• T.H. Johnson discovered that the ionization rate
  increased from east to west viewing angle
  indicating they were positively charged particles
  (protons). The increase occurs because the rays
  are deflected by the earths magnetic field, which
  changes in its strength with latitude.

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Charged Particles!

• In 1929 a Russian scientists, D. Skobelzyn,
  discovered ghostly tracks made by cosmic rays in
  a cloud chamber.
• Also in 1929 Bothe and Kolhorster verified that
  the cloud chamber tracks were curved. Thus the
  cosmic radiation was charged particles.

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The Caltech Cloud Chamber

• Milliken became President of Caltech and was
  instrumental in the building of a high magnetic
  field cloud chamber.
• Carl Anderson and Milliken made numerous
  photographs of both positive and negative
  particles tracks.
• The conclusion was that the positive particles
  must be protons.

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Occhialini and Blackett

• Giuseppe Occhialini and Patrick Blackett devised
  a method of making cosmic rays take their own
  photographs.
• They observed in 1932 the formation of multiple
  particles, pair production.
• Occasionally they observed the production of
  particle showers using lead and copper plated
  places in the cloud chamber.

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Extensive air showers

• Pierre Auger noticed that two detectors located
  several meters apart detected particles at the
  same time. He discovered EAS, showers of
  secondary nuclei produced by the interaction of
  the primary particle with air molecules. (1938)

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EAS

• It is the secondary particles resulting from the
  interaction of the the primary particle that are
  detected by the detectors used in our detectors
  and others arrays.

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An Extensive Air Shower

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

• Certain particles never reach the surface.
• Some particles, such as muons, do reach the
  surface and can be detected.
• It is these that we wish to detect.

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Other tools The emulsion plate

• The study of cosmic rays was greatly enhanced by
  the use of photographic emulsion plates. The
  plates were taken to numerous places, including
  the Pyrenees and left for extended periods of
  time.
• The results were images of complete pion decays
  including the discovery of the so called
  strange particles.

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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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Early Discoveries from CR

• The mass of the proton was determined to a 15
  error (Anderson, Chadwick)
• The discovery of the antiparticle of the
  electron, the positron (Klemperer).
• The discovery of the mesotron, with mass between
  the electron and the proton
• The first evidence of meson decay (Williams and
  Roberts)
• The measurement of the decay (Rossi)
• The discovery of He nuclei and heavier elements
  in CR (Frier)

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Present Cosmic Ray Studies

• Cosmic Ray studies continue in spite of the
  development of high energy particle accelerators.
• The energy of the highest energy cosmic rays
  still cannot be duplicated in accelerators.
• The field is still very active as indicated by
  the presentation of over 300 papers at the most
  recent international conference on cosmic rays.

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What are 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 the range 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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The Energy Spectrum

• 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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The Oh My God Particle

• In 1991 at the Flys Eye CR observatory in Utah a
  primary particle of 3 x 1020 eV was recorded.
  This is the equivalent of 51 joules
• At present particle accelerators can reach
  energies of 1012 eV.
• The Fly Eye
• (from www.physics.adelaide.edu)

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The AGASMA EVENT

• In Japan, in 1993, the worlds largest array
  recorded a large air shower believed to be the
  result of a primary particle measured at 1021 eV.
  These particles have energies six times higher
  than present theories allow.
• The mystery is, of course, what is the source of
  the high energy particles including these
  ultrahigh energy particles.

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Where do they 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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The ultra high particles?

• Without going into great detail the problem with
  the source of the UHECR is that to achieve the
  high energies they must originate in a very large
  extragalactic field or from a process that
  doesnt require such distance.
• Suggestions abound but there is not a agreement
  as to the origin. Maybe there isnt a single
  source.
• One suggestions is that UHECREs originate from
  the decay of more primary particles resulting
  from the big bang.

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A Summary

• Lower energy, lt 1016 eV
• Direct observation possible, 85 are protons.
• Most likely source are supernova shock wave
  acceleration.
• These are particles below the knee in the energy
  spectrum.

• Ultra High energy, gt 1016 eV.
• Only indirect EAR shower information is
  available.
• Source of the particles with gt 1016 eV is
  unknown.

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High School Based Detectors

• Numerous detector arrays using high schools as
  sites for individual detectors have been built or
  are in the process of development.
• 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 75000 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.

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Tentative Plans 3-week quarknet workshop.
Summer, 2004 Julia ThompsonProf. of Physics,
Univ. of Pittsburgh Adjunct Prof. of physics
and/or in participating in a proposed project to
put cosmic ray detectors in high schools,
eventually perhaps linking them into a shared
network. Teachers can register for 1-3 credit
hours from UMSL for the workshop, and will
receive a personal stipend of 300./week,
Physics, Univ. of Missouri at St. Louis A 3-week
summer workshop for physics teachers is expected
at the University of Missouri at St. Louis (UMSL)
in summer, 2004. through the quarknet program
The workshop would be open to area high school
physics teachers interested in expanding their
knowledge of current modern and a 250.
instructional materials stipend.