Galactic Cosmic Rays (GCRS)

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• Galactic Cosmic Rays (GCRS)
• Galactic cosmic rays (GCRs) come from outside
  the solar system but generally from within our
  Milky Way galaxy.
• GCRs are atomic nuclei from which all of the
  surrounding electrons have been stripped away
  during their high-speed passage through the
  galaxy.
• They have probably been accelerated within the
  last few million years, and have traveled many
  times across the galaxy, trapped by the galactic
  magnetic field.
• GCRs have been accelerated to nearly the speed of
  light. As they travel through the very thin gas
  of interstellar space, some of the GCRs interact
  and emit gamma rays, which is how we know that
  they pass through the Milky Way and other
  galaxies.
• The elemental makeup of GCRs has been studied in
  detail , and is very similar to the composition
  of the Earth and solar system.
• but studies of the composition of the isotopes in
  GCRs may indicate the that the seed population
  for GCRs is neither the interstellar gas nor the
  shards of giant stars that went supernova. This
  is an area of current study.

http//helios.gsfc.nasa.gov/gcr.html
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• Solar cosmic rays (SCR)
• The solar cosmic rays (SCR) originate mostly from
  solar flares.
• Composition is similar to galactic cosmic rays
  mostly protons, about 10 of He and lt1 heavier
  elements.
• Solar cosmic rays were firstly discovered
  experimentally on 28 February 1942, as a sudden
  increase of Geiger counters counting rate
  associated with a large solar flare.
• Since that time detectors, set up to monitor
  cosmic rays, have occasionally seen sudden
  increases in the intensity of the radiation
  associated with outbursts on the Sun, mostly with
  visible flares.
• The cosmic ray intensity returns to normal within
  tens of minutes to hours, as the acceleration
  process ends and as accelerated ions disperse
  throughout interplanetary space.
• The short increases of cosmic ray detectors count
  rate associated with solar particles arrival are
  called GLE - Ground Level Enchancement / Ground
  Level Events.

http//www.oulu.fi/spaceweb/textbook/scr.html
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• Primary and Secondary Cosmic Rays
• There are two categories of cosmic rays primary
  and secondary cosmic rays.
• Real (or "primary") cosmic rays can generally be
  defined as all particles that come to earth from
  outer space. These primary cosmic rays generally
  do not make it through the earth's atmosphere,
  and constitute only a small fraction of what we
  can measure using a suitable set of particle
  detectors at the earth's surface.
• we do measure particles at sea level in such
  detectors. What we measure, however, are mostly
  the remains from interactions of primary cosmic
  rays with the upper atmosphere. These remnants
  are also particles, referred to as "secondary"
  cosmic rays. Often, however, the specification
  "primary" or "secondary" is omitted.
• secondary cosmic rays are neither "rays" nor
  "cosmic" they are particles rather than rays,
  and they come from the upper atmosphere rather
  than outer space. On the other hand, they are
  produced by real cosmic rays!

http//www.oulu.fi/spaceweb/textbook/scr.html
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Unexpected observation in experiment

• Measuring the conductivity of gases.
• In spite of careful precautions, a significant
  residual conductivity remained.
• While by lead shielding, the residual
  conductivity reduces.
• Conclusion external radiation of some form

Cosmic Rays----A.W.Wolfendale
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• First hypothesis these radiations from
  radioactive materials in the earth
• Then gas chambers flew in balloons to study the
  variation of conductivity with height
• Decreased with height from ground to about 700
  meters, then increased steadily.
• Hess put forward the increase was due to an
  extremely penetrating radiation which was coming
  from outer space.
• From absence of any significant difference in
  conductivity between day and night experiments,
  he deduced that the radiation was not of solar
  origin. This radiation soon came to known as the
  cosmic radiation.

Cosmic Rays----A.W.Wolfendale
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• it was interpreted as ?-ray at first.
• Then it was founded they were positively charged,
  not ?-ray.
• According to the absorption properties of the
  cosmic radiation, it showed there were two main
  components the hard (penetrating), the soft
  (easily absorbed)
• Postulation the mass of penetrating particles
  between that of electron and the proton.-----µ
  mesons.( two hundred electron masses)
• future investigated that p-mesons could explain
  the decay of cosmic ray

Cosmic Rays----A.W.Wolfendale
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• Then general features of cosmic ray were clear
• high energy protons from outside the earths
  atmosphere interact with the nuclei of the
  atmosphere to produce p-mesons and small numbers
  of other particles. Many of the p-mesons decay
  to form µ mesons ( muon) which survive down to
  ground level to from the penetrating component.
  Some µ mesons decayed to electrons which
  contribute to the soft component.

Cosmic Rays----A.W.Wolfendale
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• The primary cosmic rays

Interactions of the particles can be divided into
two main processes Physical interaction
scattering, disintegration on collision with
galactic atoms Magnetic interaction deflection
of cosmic ray trajectories by the magnetic fields
Cosmic Rays----A.W.Wolfendale
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• Interactions of cosmic rays
• Electromagnetic interactions a fast charged
  particle passing through the medium atoms, energy
  transferred to the atom as a whole, excitation or
  ionization take place.
• Excitation---an electron jumped to a larger
  radium and when it fell back (de-excitation),
  radiation is emitted.
• Ionization electron is removed completely from
  the atom
• When energy gained by the electron is much
  higher, the interaction can be considered solely
  as being between particle and the electron.

Cosmic Rays----A.W.Wolfendale
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• probability of collision between a particle and a
  free electron
• Energy and momentum conservation for collision
• The probability increases with the thickness of
  the medium passed and with its density. Then
  using thickness expressed in units of mass per
  unit area, g/cm2

Cosmic Rays----A.W.Wolfendale
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• Interaction of photons (?-ray )with matter
• Three electromagnetic processes by which photons
  loses energy photo electric effect, Compton
  scattering and pair production
• Elt100keV,photo electric effect
• atom absorbs the photon, ejects electron. the
  number of photons reduced exponentially.
• Compton scattering
• photon strikes an electron and rebounds with
  reduced energy
• Pair production
• Energy converts to mass, a high energy photon
  becomes an electron pair.

Cosmic Rays----A.W.Wolfendale
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• Nuclear interactions of cosmic rays
• Experiments of Blau and Wambacher in 1937
  stars in photo graphic emulsions.
• Then it is found that stars are mainly produced
  by neutrons and protons, nuclear disintegrations
• p-mesons, then experiences more interactions.

Cosmic Rays----A.W.Wolfendale
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• Cosmic rays in the atmosphere and at sea level

Energy of a few tens of Gev, Low energy
particles cant reach Sea leavel
Cosmic Rays----A.W.Wolfendale
Nuclear cascade schematic diagram
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http//zebu.uoregon.edu/js/glossary/cosmic_rays.h
tml
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Rossi(1952),total intensity of the various
particles measured as a function of
Altitude p----protons, corresponding to
exponential proton absorption, falls down as a
straight line in log-linear graph. ?---meson,
rise rapidly to a maximum, by p meson decay.
then falls off slowly by decaying into
electrons. e----electron, same way as u meson.
More higher peak due to p meson can
lead to many electrons.
Cosmic Rays----A.W.Wolfendale
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http//www.ngdc.noaa.gov/stp/SOLAR/COSMIC_RAYS/cos
mic.html