Tracking Cosmic Ray Muons Using a Cloud Chamber

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Tracking Cosmic Ray Muons Using a Cloud Chamber

• Leah Wilson and Lori Wilson
• duPont Manual High School
• and
• Dr. Akhtar Mahmood
• Bellarmine University

KAPT 2009 SPRING MEETING MARCH 7,
2009 BELLARMINE UNIVERSITY
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Purpose and Hypothesis

• Cosmic rays are all around us, one type of cosmic
  ray that strikes the earth is a muon (µ).
• On average, one muon strikes the fingertip every
  single minute.
• In order to determine the muon flux count (number
  of muons hitting the earths surface in a given
  area per minute), a cloud chamber was constructed
  out of a basketball display case to determine the
  muon flux in the Louisville area.
• This experiment was conducted at Bellarmine
  University in a Physics Lab.
• The muon flux count obtained by our cloud chamber
  was also compared with the muon flux data
  obtained on-line from the Cosmic Ray Detector
  located at SLACs (Stanford Linear Accelerator
  Center) Visitors Center.

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Background Information

• The history of cosmic rays started in the
  beginning of the 20th century.
• In 1912, Victor Hess was in his hot air balloon
  soaring at an altitude of about 5,000 meters.
  When he was sailing around he noticed
  penetrating radiation coming from outer space.
• Following the ideas of Hess was Robert Millikan
  in 1925 who introduced the name cosmic rays.
• In 1929 Dimitry Skobelzyn built the first cloud
  chamber to test the theory of cosmic rays.

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Background Information

• In 1935, the Explorer II balloon mission ascended
  to 22,066 meters in space while collecting data
  about cosmic rays.
• In 1937, Seth Neddermeyer and Carl Anderson
  discovered the muon using a cloud chamber.
• In a major discovery in 1938, Pierre Auger
  discovered "extensive air showers" in the outer
  atmosphere. These showers were made up of
  secondary subatomic particles caused by the
  collision of high-energy cosmic rays with air
  molecules, which is now defined as a cosmic ray
  shower.
• In 1947, Cecil Powell of Bristol University in
  the United Kingdom, discovered a new type of
  cosmic ray called the pion (?).

Explorer II balloon
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Background Information (contd)

• Most muons come from what are known as cosmic
  rays. A muon is roughly 200 times heavier than an
  electron.
• There are two categories of cosmic rays primary
  and secondary cosmic rays.
• Primary cosmic rays can generally be defined as
  all particles that come to earth from outer
  space.
• When these primary cosmic rays hit Earth's
  atmosphere, they ionize the atmosphere forming a
  shower of matter and anti-matter particles.

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Background Information (contd)

• This is where the muons come from they are the
  results of an interaction between a proton (which
  are abundant in the universe) and the atmosphere
  that produces a pion that decays into a muon,
  among other particles.
• Primary cosmic rays are particles such as a
  single proton (nuclei of hydrogen about 90 of
  all cosmic rays) traveling through the
  interstellar medium. Most of these originate
  outside of the solar system (i.e. from
  Supernovae), but some of them come from the sun.
• When such a high-energy proton hits the earth's
  atmosphere at around 30000m above the surface, it
  will collide with a nuclei of the atmospheric gas
  molecules. As a result of this collision, many
  secondary particles are produced, including lots
  of particles called pions.

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Background Information (contd)

• A (charged) pion decays to a muon and two
  muon-neutrinos (which is neutral therefore can
  not be seen) at about 10000m (10 km) altitude.
• Some of these muons can make it through the
  earth's atmosphere which can be detected and
  measured using a suitable particle detector (such
  as a cloud chamber or a muon detector) at the
  earth's surface. In cosmic ray showers, both
  muons and anti-muons are produced.
• Although the muon at rest has a lifetime of only
  2.2 µs, it should have decayed after traveling a
  distance of only 660m. Thus one would conclude
  that muons produced at this high altitude of
  10000m from earth should not reach the ground.
• But muons can travel all the way down from a
  height of 10000m (10 km) above the surface of the
  earth while traveling at 99.8 the speed of
  light.

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Background Information (contd)

• The reason is that according to Einsteins
  Special Theory of Relativity, the muons age more
  slowly (in fact, about 16 times) since they are
  traveling very fast at about 99.8 the speed of
  light. This effect is called time-dilation.
• From the point of view of an observer on Earth
  the muons new lifetime can be determined from
  Einsteins Special Theory of Relativity.

• c speed of light, v speed of the muon which
  is 0.998c. (I.e. 99.8 the speed of light) and t0
  lifetime of muon at rest which is 2.2 x
  10-6 s.
• Thus this relativistic time dilation allows the
  muon to travel about 16 times farther (10000m
  instead of 657m) than would have been expected
  otherwise.

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Background Information (contd)

• We hypothesized that a using a cloud chamber, the
  muon flux count rate will be at least a factor of
  10 or less since we are using our naked eye to
  detect the muon tracks instead of the
  sophisticated muon detector.
• The latitudes of Palo Alto (37?) and Louisville
  (38?) are very close (within 1? of each other).
• Whereas Palo Altos elevation is about 262 ft.,
  and Louisvilles about 466 ft. The elevation of
  difference of about 200 ft should not result in
  any significant difference in the muon flux count
  rate except for the resolution of the two types
  of detectors.

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Background Information (contd)

• When a charged particle passes through a
  particular substance it can ionize the
  surrounding particles and leave a trail.
• For example, in a cloud chamber, the air is
  cooled to the point that when an atmospheric
  particle is ionized, it will cause the air to
  condense and thus leaves a visible trail.
• The cloud chamber is essentially saturated with
  alcohol vapor. The dry ice keeps the bottom very
  cold, while the top is at room temperature. The
  high temperature at the top of the chamber means
  that the alcohol in the felt produces a lot of
  vapor, which falls downwards. The low temperature
  at the bottom means that once the vapor has
  fallen, it is supercooled. It is in a vapor form,
  but at a temperature at which vapor normally
  can't exist. Since the vapor is at a temperature
  where it normally can't exist, it will very
  easily condense into liquid form.
• When an electrically charged cosmic ray comes
  along, it ionizes the vapor--that is, tears away
  the electrons in some of the gas atoms along its
  path. This leaves these atoms positively charged
  (since it removed electrons, which have negative
  charge). Other nearby atoms are attracted to this
  ionized atom. This is enough to start the
  condensation process.

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Types of Cosmic Ray Muon Tracks

• The Figure on the left is an example of a cosmic
  ray muon track.
• The muon track can be seen coming straight which
  then "kinks" off to the left sharply after
  knocking off an electron from the atom in the
  material.

Example of a Muon Track
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• Figure to the left is an example of a very jagged
  muon track. This is known as "multiple
  scattering", where a low-energy cosmic ray
  bounces off of one atom in the air to the next.
• Figure to the left is the third example of a muon
  track. It shows a muon decaying into an electron
  and two neutrinos (actually one electron-neutrino
  and one anti-electron neutrino)

Another Example of a Muon Track
Yet Another Example of a Muon Track
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Procedure

• The cloud chamber was constructed to consistently
  produce an environment
• where muon tracks could be detected.
• Felt pads were saturated with 91 isopropyl
  alcohol inside of the chamber (only on the top
  and bottom sides) with the goal of creating a
  super-saturated atmosphere of alcohol within the
  chamber.
• The chamber was then set on a block of dry ice
  and was cooled to create the required environment
  for muon detection.

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Procedure (contd)

• To build the cloud chamber the following
  materials were needed -
• A basketball display box, a conducting sheet of
  metal, silicon cement, razor blades,
  weather-strip, black felt, four push-pins,
  Windex, 91 pure isopropyl alcohol and
• paper towels.
• First, we replaced the bottom of the display box
  with the thin sheet of conducting metal.
• We used silicon cement to ensure firm
  placement of the metal at the bottom.
• Next, we took the same silicon cement
• and ran it around the inside and outside
  edges of the display box to make sure that no air
  will be able to get into the box when the
  experiment is going on.

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Pasteur Hall
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Procedure (contd)
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Procedure (contd)

• We placed the cloud chamber on top of the dry ice
  block and then turned off the lights and shone a
  high intensity light through the center/side of
  the chamber.
• We waited for the fog to form at the bottom and
  begin to time the twenty minutes.
• At every minute mark, we tallied the number of
  cosmic rays observed within the twenty minutes
  and repeated the experiment five times.

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CLOUD CHAMBER RESULTS
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Results
The cosmic ray muons detected in each 20 minute
five trial run varied from 0 17.
This figure shows the average number of muons per
minute.
This figure shows the same results, charted in a
bar graph.
This figure shows the average number of muons per
minute in each trial.
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Results (contd)
These are the actual pictures of muons tracks
that were detected inside the cloud chamber we
built.
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Conclusion

• The experimental data supported the goal of this
  research project, which was to measure the muon
  flux in Louisville.
• During a 100-minute time frame in 5 different
  trials, a total of 593 muons were observed or and
  average of about 119 muons per 20 minutes.
  Therefore we detected an average of 6 muons per
  minute.
• The limitation of the experimental setup was the
  effective area of observation was about one-ninth
  of the size of the box, due to the location of
  the light source that was directed at the cloud
  chamber.
• The chamber measured 30 cm (L) x 30cm (W), which
  equals an area of 900cm2, whereas the effective
  dimension of focus was about
• 10 cm (L) x 10cm (W) which gives the
  effective area of focus of about 100 cm2.

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Conclusion (contd)
SLAC Cosmic Ray Detector Data (Muon flux
count rate)
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Conclusion (contd)

• The SLAC data shows that the muon flux in Palo
  Alto was anywhere from 0.3 - 0.9 muons/min/cm2 or
  an average muon flux of 0.6
  muons/min/cm2 of during that time which
  corresponds to
• 60 muons/min/100cm2, to match with our
  effective area of observation which was about
  100cm2.
• Our hypothesis predicted that with a cloud
  chamber the expected resolution would be about
  ten times less (10 or less).
• Our cloud chamber experiment detected a mean flux
  of 6 muons/min/100cm2 (or
  0.06 events/minute/cm2) which was consistent with
  the hypothesis regarding the resolution of this
  experimental setup.

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Awards and Recognition

• March 7, 2008
• duPont Manual Science and Engineering Fair
• 2nd Place Team in Physical Science

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Awards and Recognition

• March 29, 2008
• (KYSEF) Kentucky Science and Engineering Fair
• Certificate for 1st Place Team
• Trophy for Best of Fair high school Team Project
• University of Kentucky Presidential Scholarship
  for 1st place prize in State Competition
• University of Louisville Trustee Scholarship for
  1st place prize in State Competition

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Awards and Recognition

• April 14, 2008
• Certificate of Recognition for duPont Manual High
  School Kentucky Science and Engineering Fair
  Winner presented by Jefferson County Board of
  Education

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Awards and Recognition

• April 19, 2008
• Kentucky Junior Academy of Science (KJAS) 1st
  Place Winner

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Awards and Recognition

• May 11-16 2008
• Finalist at the INTEL International Science and
  Engineering Fair
• Certificate Presented by Agilent Technologies