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The
Cosmic Ray Observatory Project (CROP), headed by principal investigators
Dr Dan Claes
and Dr Greg Snow of the University of Nebraska-Lincoln, enlists
high schools across the state of Nebraska to join a study of cosmic
rays. Equipped with detectors from a cosmic ray experiment which
had run its lifetime, CROP hopes to situate detectors in schools
across the state of Nebraska. Initiated in 2000, CROP began with
five high schools and has now expanded to sixteen schools.
 To report progress
with the study of cosmic rays, to resolve problems with equipment, to answer
questions and to establish future goals for the experiment, the participants
of CROP gather at the University of Nebraska twice year. The most recent meeting
took place January 18, 2003. The first significant event of the meeting was the
announcement of Dr Claes and Dr Snow that data acquisition cards for the CROP
experiment will be going into production in February 2003. The data acquisition
cards allow a computer to monitor and record the arrival of cosmic rays when
they are seen by the detectors. To the present time, all data from the experiment
has been recorded manually. The data acquisition cards will allow more information
to be recorded and stored with much less human intervention. In addition the
cards are fitted with a Global Positioning Satellite (GPS) receiver. The GPS
system allows the time and location of any place on earth to be determined by
monitoring signals from an array of satellites in space. With the GPS system
on board the data acquisition cards, the location and arrival time of cosmic
rays can be carefully recorded. This information is significant for determining
the direction from which cosmic rays arrive at the earth.
The second significant event was the distribution of new high voltage power supplies.
To allow the detectors to see cosmic ray particles, a high voltage is required.
The first high voltage power supplies distributed were not stable. Instead of
holding at the required voltage, they tended to vary widely and unpredictably.
The new power supplies use a regulator to keep the voltage from changing. Additionally,
a display on board the power supply allows for the voltage to be monitored.
Mount Michael students
made two presentations at the January CROP meeting. The first report was given
by seniors Dan Olson, Mark Hotovy and Ryan Steifvater.
The seniors attempted an experiment to measure the mean lifetime of a muon. When
a particle from space collides with nuclei in the earth's atmosphere, a shower
of particles is produced. A major constituent of these showers is the muon. The
muon is a close relative of a more familiar particle, the electron, which is
found in all ordinary matter. The muon however is not a stable particle like
the electron, and it will eventually decay into other particles. Since so many
muons are produced in cosmic ray showers, it is possible to catch a few of them
in the act of decaying. With enough information, one can then find the average
lifetime of the muon. Though many hours were put into the experiment, Olson,
Hotovy and Stiefvater reported that they had not yet collected enough meaningful
data to make a statement about the lifetime of the muon. It is hoped that the
experiment will continue into the next semester of school. By that time, it should
be possible to make some statement about the muon's lifetime.
The second report
was given by juniors Mike Lundgren, A J Killeen and Ben Swiniarski. The juniors
compared the flux of cosmic rays to the radioactive background monitored
by a Geiger counter. To determine the cosmic ray flux, three detectors were stacked
vertically, one atop another. A count was recorded only if all three detectors
saw the passage of a cosmic ray. The CROP detectors are sensitive primarily to
muons, electrons and positrons. On the other hand, a Geiger counter sees alpha
rays, beta rays and gamma rays. Alpha rays are helium nuclei minus their electrons.
Beta rays are electrons and positrons. Gamma rays are high energy photons. The
two detectors overlap in seeing electrons and positrons, but not in the other
particles. The purpose of the experiment was to see if there was any relation
between cosmic ray activity and radioactivity. Each day, three times a day, the
studetns would simultaneously measure the cosmic ray activity and the radioactivity.
Beginning in September, the students continued their measurements until the end
of November. Plotting the cosmic ray activity versus the radioactivity showed
no significant dependence of one on the other.
The papers produced
by the students ("The Mean Lifetime of a Muon",
Olson, Hotovy and Stiefvater and "Comparing Cosmic Rays and Radioactivity",
Lundgren, Killeen and Swiniarski) can be found on the CROP page of the Mount
Michael web site. The power point presentations which the students made as a
part of their report are also posted on the CROP page.
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