Abstract

Muons are created when cosmic radiation (usually protons) decay upon interacting with Earth's atmosphere.  We used a scintillation detector with four seperate counters in order to measure the time delay between events in each counter.  We graphed the time delays against the distance between each counter and used the slope of the graph to determine the average speed of the incoming muons.

Introduction

We are interested in finding the velocity of incoming muons in an effort to gain more information about them.  Specifically, we are attempting to determine if they move at relativistic speeds.

Procedures

1. Place two scintillator counters (counters 1 and 4) a specific vertical distance apart.
2. Record the number of signals from each counter in a given time interval.
3. Discard all data that doesn't correspond to a coincidence between the two counter signals.
4. Find the difference in time between counter signals for each coincidence.
5. Repeat the above steps for multiple distances.
6. Graph time difference vs. distance and calculate the slope as velocity^-1.

Results

A graph of the average time versus counter distances was created.  See Figure 1.  A best fit line was added to the graph.  The muon velocity was calculated by taking the inverse of the slope.  The average muon velocity was 0.303 m/ns.  However, there appears to be an outlier at a distance of 1.645 meters.  A second graph omitting this data point was also created and analyzed.  See Figure 2.  According to this graph, the average muon velocity was 0.311 m/ns.  

Discussions & Conclusions

The average velocities of a muon were calculated to be 0.303 and 0.311 m/ns.  These velocities are faster than the speed of light.  The experiment should be repeated.  More data points should also be collected by continuing to vary the counter distances.  Using a more precise method for measuring counter distance should be employed as well.        

Bibliography

Special thanks to Matthew Jones