1. By Rebecca Denison, Joe Ditmar, Oxana Kachtanova, Caitlin Kearns, and Sam Tencer With the greatly appreciated assistance of Maureen Michael and Stephanie Stock

2. What are Cosmic Rays? Atomic nuclei (protons and neutrons) that constantly bombard the earth Possess an enormous range of energy Generally have a positive electrical charge, and are thus deflected by magnetic fields The exact origin of cosmic rays is still unknown due to their bent trajectories

3. Cosmic Ray Detection: Cosmic rays create showers of particles when they strike Earth’s atmosphere These particles, rather than the original cosmic rays, are detected on Earth A cosmic ray shower

4. The Cosmic Ray Detector: When cosmic rays strike the scintillator paddles, electrons in the scintillator release flashes of light, which cause electrons to be released in the photomultiplier tube. The photomultiplier “multiplies” the number of electrons until there are enough to produce an electric signal, which is shown as a count on the display.

5. Phototube Noise and Coincidence: Energy unrelated to cosmic rays can cause the detector to produce a signal, creating “phototube noise” To reduce “phototube noise,” we adjusted the detector to count only events that strike both paddles. Using the paddles “in coincidence” increases the accuracy of the cosmic ray count by weeding out false signals.

6. Hypothesis: The amount of counts will vary with the time of day due to varying quantities of solar energy interfering with the travel of cosmic rays.

7. Materials: - 12 V power supply - Cosmic Ray detector - Outlet - 5-8 ft extension cord - Stopwatch - Open Location

8. Procedure: Step 1: Place the detector in an open location Step 2: Connect the extension cords and the battery + connect it to the detector through an outlet. Step 3: Simultaneously switch the clear/count labeled switch on the detector on count, and start the timer on the watch. Step 4: Stop the timer and switch the infinity/hold switch to hold after precisely 5 minutes. Step 5: Record the counts displayed on the detector in a table and remember to fill in the rest of the table of observations (including: Date, Time, Counts, Weather & Reasons for Error)

9. Collected Data:

10. Graphs:

11. Graphs:

12. Graphs:

13. Conclusions: Through our experiment, we discovered that the time of day affects the count of cosmic rays, as predicted in our hypothesis. We found that even with an average 4.55% error in the counts, there is a significant increase in cosmic ray counts as the day progresses, with the highest counts during the night. We believe that the reason for this is the increased amount of collisions between photons and cosmic rays during the day. These collisions slow down the nuclei that compose cosmic rays and therefore make them undetectable.

14. Reasons for Error: Systematic: oOutlet and prongs of cord not securely connected during entire trial oUse of different watches during different trials oUse of different timekeepers during different trials oChange of outlet oCalibration of cosmic ray detector oWiring Random Uncertainty: oUse of umbrella and towel during certain trials oShadows from buildings and people during the day oDelay between starting/stopping watch and switching the switches off oVarying weather conditions (sunny, cloudy, rain, etc.) oVarying outdoor environment (electric lights, noise, traffic, etc.)

15. Suggestions for Improvement: Greater consistency in use of equipment (same watch, electrical outlet, etc.) Use one 15-minute trial rather than three 5-minute trials to reduce delay between starting timer and starting count Compare cosmic ray detector to another detector to ensure a more standard calibration Do all measurements on the same day to eliminate differences in sunrise/sunset and reduce differences in weather Change location to one with less traffic, lights, and shadows Do the same experiment, but change the factor we are looking at by changing time of day to weather