NSCL Cosmic Ray Experiment

Originally a Word Document, PDF form: cosmic_directions.pdf

How the CRD Works | Operating the CRD | Experiment | Analysis

Cosmic Ray Experiment (with Real Nuclei from Outer Space!)

Materials:

earth
Figure 3  Cosmic rays approaching detectors
like those you will work with.

You Provide:
Pencil or Pen
Notebook

NSCL Provides:
Cosmic Ray Detector
Protractor
Plumbob
String
Supportive materials
Stopwatch
Calculator
Rulers

Universe Provides:
Cosmic Rays


Objective:  Find out how the frequency of cosmic rays changes with the angle between the detector and the earth’s surface.

Hypothesis:  From which direction do cosmic rays reach the earth’s surface?  Do you think they come in perpendicular to the earth, or parallel to the earth?  Write down your hypothesis.

Prediction:  How do you think the angle will affect the cosmic ray count rates?  Do you think the detector will report more counts when it is horizontal (catching rays perpendicular to the earth’s surface) or vertical (catching rays parallel to the earth’s surface)? **   Write down your prediction.

**For this experiment, the words horizontal and vertical refer to the detector while parallel and perpendicular to the earth’s surface refer to the cosmic rays.
 

Procedure: 

  1. Set the switches on the cosmic ray detector so that the buzzer (switch A) is off and coincidence events are counted (switch B).  Set the switch C to “hold count.”  Clear the count by moving switch D to “clear” and then moving it back to “count.”
  2. Set the cosmic ray detector on its end (vertical position) so that it catches rays coming in parallel to the earth’s surface.  You will have to hold it in this position.
  3. You and your partner should start the stop watch and switch the count mode to “infinite” at the same time. 
  4. Let the cosmic ray detector count for 180 seconds (3 minutes).
  5. Stop your watch, switch the count mode to “hold count,” and record the count in the table under 90 degrees.
  6. Using the protractor, string, and plumbob, set up your cosmic ray detector so that it is at an angle of 75 degrees from the ground.  Use the supports provided to hold it there.
  7. Move switch D to “clear” and switch C to “hold count.  Then put switch D back to “count.”
  8. Simultaneously put switch C back on “infinite count” and start the stopwatch, again counting for 180 seconds.
  9. Repeat the process until you have recorded times for 90˚, 75˚, 60˚, 45˚, 30˚, 15˚, and 0˚.  At zero degrees, the detector should be in the horizontal position, catching rays perpendicular to the earth’s surface.

 

Angle (degrees)

90

75

60

45

30

15

0

Number of counts

 

 

 

 

 

 

 

Count Rate (counts/second)

 

 

 

 

 

 

 

Error in Count Rate