Near Space
error, I got burned when correctly
answering a question about the
electromagnetic spectrum during
tryouts for the College Bowl in 1981.
The Source of
Cosmic Rays
Cosmic Rays as a Tool of Science
The first particle accelerators
were built less than 100 years ago.
These first generation devices
couldn’t reach very high energies.
So, to study subatomic physics,
physicists launched their experiments in high altitude balloons,
where they could use cosmic rays as
their source of high energy subatomic particles. The results of these
experiments led to the discovery of
several important subatomic
particles.
One subatomic particle discovered in cosmic ray experiments was
the meson. The meson was predicted to exist and be responsible for
holding the nucleus of the atom
together. There are actually several
types of mesons — like the mu and pi
mesons (called the muon and pion)
— and only one is responsible for
keeping the protons inside the
nucleus together. As it turns out, the
first meson discovered was not the
one found inside the nucleus.
Another particle discovered from
cosmic ray experiments was the first
anti-matter particle — the anti-electron or positron — which was
predicted by physicist Paul Dirac.
Today, particle accelerators can
reach such high energies that it’s no
longer convenient to do subatomic
research with cosmic rays. However,
that doesn’t mean cosmic rays are
no longer an item of research. Now,
cosmic rays are researched in an
effort to understand astronomical
and nuclear processes occurring in
the Sun and beyond the solar
system.
About 86% of cosmic rays are protons or hydrogen nuclei (remember,
the hydrogen nucleus doesn’t have a
neutron). Twelve percent are helium
nuclei (alpha rays), 1% are energetic
electrons, and the remaining 1% are
atomic nuclei heavier than helium;
these are elements that astronomers
call metals. There are some high
energy gamma rays and neutrinos
thrown into the mix, as well.
Their Energies
One of the most amazing aspects
of cosmic rays is their level of kinetic
energy. Some cosmic rays carry over
100 quintillion electron volts of
energy. That’s enough energy to boil
a thimbleful of water if all that energy
could be transferred to it. (In reality,
such a cosmic ray would travel right
through the water, scarcely noticing
it, and leave only a tiny bit of its
energy in the water.)
Put another way, this amount of
energy is the same as the kinetic
energy of a baseball thrown at about
100 mph! Imagine the energy of a
fast baseball packed into a single,
invisible proton. The high energy
levels found in cosmic rays allow
them to make the trip to Earth at
speeds very close to that of light.
In optical astronomy,
astronomers can point their
telescopes in the direction of the light
they are observing and see the light’s
source. However, galactic, solar, and
terrestrial magnetic fields so
thoroughly mix up the paths of
cosmic rays that other methods must
be used to determine their source.
The possible sources of cosmic rays
are determined by how they respond
to the solar cycle, their composition,
and their kinetic energy. So far, it’s
believed that there are three sources
of cosmic rays.
Solar Cosmic Rays
These cosmic rays originate with
the solar chromosphere (the solar
layer above the photosphere — the
visible surface of the Sun) during
high energy events like solar flares.
Solar cosmic rays tell us the types of
elements and their proportion
residing in the outer atmosphere of
our Sun.
These tend to be the lowest
energy cosmic rays. Their presence
goes up shortly after a flare and can
increase by a factor of hundreds to
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The Nature of
Cosmic Rays
Their Composition
The vast majority of cosmic rays
are energetic nuclei — high speed
atoms stripped of their electrons.
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