■ BY L. PAUL VERHAGE
THE NEAR SPACE GEIGER
COUNTER TELESCOPE — Part 1
MANY OF MY NEAR SPACE MISSIONS have
measured the cosmic ray flux in near space
with onboard Geiger counters. Combining
Geiger counter data with GPS altitude has
allowed me to generate charts showing the
cosmic ray flux as a function of altitude.
Experiments like this allowed the Austrian
physicist Victor Hess to prove the existence
of cosmic rays in 1911-1913.
■ FIGURE 1. A mission-ready Geiger counter telescope.
The chart in Figure 2 is an example
of the cosmic ray data from my
near space flights. Notice that the
cosmic ray count rises from about
eight counts per minute (CPM) at the
surface (an elevation of 2,400 feet at
home) to a maximum of around 700
CPM at an altitude of 62,000 feet.
Surprisingly though, the cosmic ray
count decreases above 62,000 feet.
It took me a few days to discover
why the cosmic ray flux decreases at
the highest altitudes. When a cosmic
ray enters Earth’s atmosphere, it
slams into a molecule in the air and
shatters it. This collision creates a
shower of secondary cosmic rays that
■ FIGURE 2. Example of cosmic-ray data.
TV03I Cosmic Ray
300 400 500
continue towards the surface. A
secondary cosmic ray can create additional secondary cosmic rays though
collisions. The decreased cosmic ray
flux above 62,000 feet is therefore an
indication that only original (primary)
cosmic rays are being detected. They
haven’t yet had a chance to collide.
After enough collisions, however,
most secondary cosmic rays have
so little energy that they are
undetectable at the Earth’s surface.
So on the surface, we’re detecting
only those cosmic rays that survived
collisions with molecules in the air.
This introduction has so far
discussed only the history of a cosmic
ray after it enters our atmosphere, not
what a cosmic ray is. Most cosmic rays
are hydrogen nuclei or protons. There
are also some helium nuclei (alpha
particles) thrown into the mix along
with the nuclei of heavier atoms,
energetic electrons, and a few gamma
rays. Where does this zoo of subatomic particles come from? Today it’s
800 believed they originate in supernova
explosions and from the sun.