Jimmy McCarthy International Cosmic Ray Day 26 th September
2012 Detecting Cosmic Rays
Slide 2
The Detector
Slide 3
The Scintillation Counter Plastic scintillator Charged particle
goes through scintillator. Light emitted in all directions. Light
bounces around scintillator. Enters light guide. Directed into
PMT
Slide 4
Photomultiplier Tube Photon hits cathode. Electron is emitted
from cathode. Hits dynode and 2 or 3 electrons emitted. Amplified
at each stage Electrical signal produced. Photon Anode Electron
DynodesPhotocathode
Slide 5
The QuarkNet Card ddddfd Signal In Check for coincidences
Counting cosmic rays Connect to computer
Slide 6
The Experiments Split into 3 groups 3 different experiments
11:00 12:15 Getting familiar with equipment 12:15 1:15 Lunch 1:15
2:15 Collecting Data 2:15 3:15 Analysing Data
Slide 7
Measuring Flux (All 3 experiments) Flux is the number of cosmic
rays passing through the detector every second. Using the counter
on the QuarkNet board. What errors might arise using this method?
Using 6 people to get results. 1 person to keep time. 2 people to
record and process counts 3 people to read the counter each minute
Every 30 secs, 3 people shout out the number on the counter. Take
an average of the 3 numbers, and work out how many cosmic rays were
detected. Repeat for ~15 minutes (30 readings)
Slide 8
Exp1: Solid Angle Start with counters at fixed separation.
Measure the flux of cosmic rays Change the separation Measure the
flux again Discuss in groups: Do you expect to see a difference? If
so, what difference? Why? Calculate theoretical predictions. Does
it match your measurements?
Slide 9
Exp2: Zenith Angle Start at fixed separation. Measure the flux.
Change the angle of the detector to the vertical. Keep the
separation the same Discuss in groups: Do you expect to see a
difference? If so, what difference? Why? Measure more angles (from
0 90 ) Does it follow a pattern?
Slide 10
Exp3: Altitude. Start with fixed separation. Measure flux. Put
the detector on the trolley provided. Move to a different floor in
the building. Measure the flux again. Discuss in groups: Do you
expect to see a difference? If so, what difference? Why? Measure
the flux on each floor of the building. Estimate the height
difference between floors. Does the flux follow a pattern?
