Cosmic Rays are radiation from Space that enters the earths atmosphere. Cosmic radiation comes from
many sources. The Sun, Neutron stars, Black Holes, and Super Nova are examples of some of the
sources of cosmic radiation. The variety of particle energies suggests a wide variety of sources.
Cosmic Rays is really an incorrect term, they are not rays or beams of radiation. They are individual high
energy particles. About 90% of these particles are protons, about 9% are alpha particles, the remaining
1% are electrons. These particles can have extremely high energies. The magnetic fields of the galaxies
and stars alter the flight path of these particles. Because of this they generally can not be traced back to
When cosmic particles enter the earths atmosphere they interact
with the nuclui of the gas, primarily Nitrogen and Oxygen, in the
atmosphere (see fig 1). The cosmic particles from space are called
primary. The particles resulting from the collision are called
secondary. These interactions causes a stream of lighter particles.
This is sometimes called an air shower (see fig 1).
These collisions produce neutrons, and mesons (+ and - pions and
kaons).The pions are very unstable and degrade into electrons and
muons. The muons and some neutrons are the only particles that
reach the service of the earth. All of the secondary particles
follow a path that is within 1 degree of the path of the primary
Cosmic radiation also produces several unstable isotopes. A
common and useful isotope is Carbon 14. It is formed when a
proton interacts with Oxygen producing neutrons and pions (see
fig 2). The neutron than interacts with Nitrogen producing Carbon
14 (see fig 3). Cosmic radiation has kept the level of Carbon 14
in our atmosphere constant (about 70 tons) for over 100,000
We can not detect cosmic particles directly on the surface of the earth as they do not make it through
the atmosphere. What we can detect are the Muons produced in the air shower that results from the
cosmic particles interaction with the atmosphere. Muons are produced in relatively large numbers.
They are charged particles and can be detected easily with equipment designed to detect ionizing
Before you can detect Muons they must be separated from other back round radiation. One method
to do this is to use two detectors. The detectors are placed one over the other with their outputs
connected to an and gate. The and gate only produces an output pulse when there is an pulse at
both inputs at the same time. This requires that a particle has to pass through both detectors to
produce an output pulse that can be counted. This arrangement is called a coincidence detector.
I am using two Aware Electronics RM-60 detectors placed one on top of the other. The outputs are
wired to a coincidence detector and then to com 1 on a computer. One of the RM-60's output is
split, one going to the coincidence detector and the other going to com 2 on the same computer (see
The computer has two copies of the RM-60 software running in separate windows. One is
monitoring com 1 the other monitoring com 2. This gives two sets of data. One is the muon count
(com 1), the other is the back round count (com 2). The data is stored in text format and later
exported into Excel for display, graphing or study.
Cosmic Ray Detection