Download Cosmic Rays

 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

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 <1% 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
 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
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
 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

it was interpreted as γ-ray at first.
 Then it was founded they were positively charged, not γray.
 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 π-mesons could explain the
decay of cosmic ray
Cosmic Rays----A.W.Wolfendale
 Then general features of cosmic ray were clear:
 high energy protons from outside the earth’s
atmosphere interact with the nuclei of the
atmosphere to produce π-mesons and small
numbers of other particles. Many of the πmesons 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
 The primary cosmic rays
Origin
Accel.
Galactic
matter
and
fields
Solar
system
Earth’s
Field
Earth’s
atmos
General flux
Sun
Solar flux
life history of 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
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
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
Interaction of photons (γ-ray )with matter
 Three electromagnetic processes by which photons
loses energy: photo electric effect, Compton scattering
and pair production
 E<100keV,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
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
 π-mesons, then experiences more interactions.
Cosmic Rays----A.W.Wolfendale
 Cosmic rays in the atmosphere and at sea level

Energy of a few tens of Gev,
Low energy particles can’t reach
Sea leavel
Cosmic Rays----A.W.Wolfendale
Nuclear cascade schematic diagram
http://zebu.uoregon.edu/~js/glossary/cosmic_rays.html
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.
υ---meson, rise rapidly to a maximum,
by π meson decay. then
falls off slowly by decaying into
electrons.
e----electron, same way as u meson.
More higher peak due to π meson
can lead to many electrons.
Cosmic Rays----A.W.Wolfendale
http://www.ngdc.noaa.gov/stp/SOLAR/COSMIC_RAYS/cosmic.html