Cosmic Rays

1
Cosmic Rays

• Not part of the EM spectrum like UV and IR

2

• Gamma-rays have the smallest wavelengths and the
  most energy of any other wave in the
  electromagnetic spectrum.
• These waves are generated by radioactive atoms
  and in nuclear explosions.
• Gamma-rays can kill living cells, a fact which
  medicine uses to its advantage, using gamma-rays
  to kill cancerous cells.

3

• Gamma-rays travel to us across vast distances of
  the universe, only to be absorbed by the Earth's
  atmosphere.
• Instruments aboard high-altitude balloons and
  satellites like the Compton Observatory provide
  our only view of the gamma-ray sky.

4

• Cosmic rays are energetic particles that are
  found in space and filter through our atmosphere.
  
• Cosmic rays have interested scientists for many
  different reasons.
• They come from all directions in space, and the
  origination of many of these cosmic rays is
  mostly unknown.

5

• Galactic Cosmic rays are mostly pieces of atoms,
  protons electrons and atomic nuclei which have
  had all of the surrounding electrons stripped
  during their high speed passage through the
  galaxy.

6

• Most galactic cosmic rays are probably
  accelerated in the blast waves of supernova
  remnants.
• The remnants of the explosions expanding clouds
  of gas and magnetic field can last for thousands
  of years and this is where cosmic rays are
  accelerated.
• Bouncing back and forth in the magnetic field of
  the remnant randomly lets some of the particles
  gain energy, and become cosmic rays.
• Eventually they build up enough speed that the
  remnant can no longer contain them and they
  escape into the galaxy.

7

• Cosmic rays were originally discovered because of
  the ionozation they produce in our atmosphere.
• Cosmic rays also have an extreme energy range of
  incident particles, which have allowed physicists
  to study aspects of their field that can not be
  studied in any other way.

8

• In the past, we have often referred to cosmic
  rays as "galactic cosmic rays", because we did
  not know where they originated.
• Now scientists have determined that the sun
  discharges a significant amount of these
  high-energy particles.

9

• "Solar cosmic rays" (cosmic rays from the sun)
  originate in the sun's chromosphere.
• Most solar cosmic ray events correlate relatively
  well with solar flares.

10
Cosmic Rays at the Energy Frontier

• These particles carry more energy than any
  others in the universe.
• Their origin is unknown but may be relatively
  nearby

11

• Roughly once a second, a subatomic particle
  enters the earth's atmosphere carrying as much
  energy as a well-thrown rock.
• Somewhere in the universe, that fact implies,
  there are forces that can impart to a single
  proton 100 million times the energy achievable by
  the most powerful earthbound accelerators.
• Where and how?

12

• Those questions have occupied physicists since
  cosmic rays were first discovered in 1912
  (although the entities in question are now known
  to be particles, the name "ray" persists).
• The interstellar medium contains atomic nuclei of
  every element in the periodic table, all moving
  under the influence of electrical and magnetic
  fields.

13

• Without the screening effect of the earth's
  atmosphere, cosmic rays would pose a significant
  health threat indeed, people living in
  mountainous regions or making frequent airplane
  trips pick up a measurable extra radiation dose.

14

• Perhaps the most remarkable feature of this
  radiation is that investigators have not yet
  found a natural end to the cosmic-ray spectrum.
• Most well-known sources of charged
  particles--such as the sun, with its solar
  wind--have a characteristic energy limit

15

• they simply do not produce particles with
  energies above this limit.
• In contrast, cosmic rays appear, albeit in
  decreasing numbers, at energies as high as
  astrophysicists can measure.
• The data run out at levels around 300 billion
  times the rest-mass energy of a proton because
  there is at present no detector large enough to
  sample the very low number of incoming particles
  predicted.

16

• Nevertheless, evidence of ultrahigh-energy cosmic
  rays has been seen at intervals of several years
  as particles hitting the atmosphere create myriad
  secondary particles (which are easier to detect).
  
• On October 15, 1991, for example, a cosmic-ray
  observatory in the Utah desert registered a
  shower of secondary particles from a 50-joule (3
  x 1020 electron volts) cosmic ray.

17

• Although the cosmic-ray flux decreases with
  higher energy, this decline levels off somewhat
  above about 1016 eV, suggesting that the
  mechanisms responsible for ultrahigh-energy
  cosmic rays are different from those for rays of
  more moderate energy.

18

• In 1960 Bernard Peters of the Tata Institute in
  Bombay suggested that lower-energy cosmic rays
  are produced predominantly inside our own galaxy,
  whereas those of higher energy come from more
  distant sources.
• One reason to think so is that a cosmic-ray
  proton carrying more than 1019 eV, for example,
  would not be deflected significantly by any of
  the magnetic fields typically generated by a
  galaxy, so it would travel more or less straight.

19

• If such particles came from inside our galaxy, we
  might expect to see different numbers coming from
  various directions because the galaxy is not
  arranged symmetrically around us.
• Instead the distribution is essentially
  isotropic, as is that of the lower-energy rays,
  whose directions are scattered.

20
Supernova Pumps

• Such tenuous inferences reveal how little is
  known for certain about the origin of cosmic
  rays.
• Astrophysicists have plausible models for how
  they might be produced but no definitive answers.
  

21

• This state of affairs may be the result of the
  almost unimaginable difference between conditions
  on the earth and in the regions where cosmic rays
  are born.
• The space between the stars contains only about
  one atom per cubic centimeter, a far lower
  density than the best artificial vacuums we can
  create.

22

• http//www.sciam.com/0197issue/0197swordy.html
• http//helios.gsfc.nasa.gov/cosmic.html
• http//zebu.uoregon.edu/js/glossary/cosmic_rays.h
  tml
• http//www.geocities.com/SunsetStrip/1483/ozone.ht
  ml
• http//science.msfc.nasa.gov/newhome/headlines/ast
  26mar99_1.htm

23

• http//www.mpihttp//helios.izmiran.troitsk.ru/cos
  ray/main.htm
• hd.mpg.de/hfm/CosmicRay/CosmicRaySites.html

24

• Galactic Cosmic rays are high energy particles
  that flow into our solar system from far away in
  the galaxy. Galactic Cosmic rays are mostly
  pieces of atoms, protons electrons and atomic
  nuclei which have had all of the surrounding
  electrons stripped during their high speed
  passage through the galaxy.
• Most galactic cosmic rays are probably
  accelerated in the blast waves of supernova
  remnants. The remnants of the explosions
  expanding clouds of gas and magnetic field can
  last for thousands of years and this is where
  cosmic rays are accelerated. Bouncing back and
  forth in the magnetic field of the remnant
  randomly lets some of the particles gain energy,
  and become cosmic rays. Eventually they build up
  enough speed that the remnant can no longer
  contain them and they escape into the galaxy.
• http//helios.gsfc.nasa.gov/cosmic.htmlcractys
• http//www.geocities.com/SunsetStrip/1483/ozone.ht
  ml
• http//science.msfc.nasa.gov/newhome/headlines/ast
  26mar99_1.htm

25
http//www.sciam.com/0197issue/0197swordy.htmlht
tp//www.mpihttp//helios.izmiran.troitsk.ru/cosra
y/main.htm-hd.mpg.de/hfm/CosmicRay/CosmicRaySites.
html
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