1. Compton Scattering Experiment John Klumpp And Ainsley Niemkiewicz

2. What is Compton Scattering? Occurs when incident photon interacts with free electron Produces scattered photon and recoil electron

3. What Does it Predict? The energy of the scattered photon is dependent on the angle of its deflection. Expressing energy in terms of wavelength, this relation reads: Or, alternatively, 1/E – 1/E o = m -1 (1 – cos(θ))

4. What About the Scattering Cross Section? This is predicted by the Klein-Nishina Formula:

5. What Does Measuring Compton Scattering Tell Us? Electron Mass Highly suggestive of the particle properties of photons Refutes Classical Scattering

6. How Do We Measure Compton Scattering? Scatter gamma rays from a Cesium 137 source against a copper target Detect scattered photons using scintillation detector which revolves about the target

7. Calibrate MCA using peaks of Cs 137, Ba 133, Co 57, and Co 60 and their known energies Collect data for angles 30  -90  in increments of 10 , and angles 105  -150  in increments of 15 

8. Calibration Data IsotopePeak Value Channel NumberEnergy Co 60 (1 st Peak)16691.173 Ba 133 853.40.356 Co 60 (2 nd Peak)18341.330 Cs 137 12360.662 Co 57 299.80.1237

9. Scattering Data Angle (Degrees) Peak Position (Channel Number) Peak Position (Energy) Area (Number of Counts) 301106 0.552449 2878 401048 0.505295 2761 50981.8 0.454495 1520 60915.2 0.406636 2130 70846.1 0.360425 2120 80785.4 0.322725 1841 90734.5 0.293199 1688 105670.3 0.258671 209.5 120593.2 0.221207 554.6 135536 0.196235 2729 150496.9 0.180547 2868

10. Energy Peaks Subtract background Calculate energy at each angle

11. Energy vs. Angle The slope of this line represents the inverse of the electron mass. Result: M = 474 keV

12. Cross-Section Comparison

13. Sources of Uncertainty Statistical -Uncertainty on energy ~ 0.15% – 0.3% -Total statistical uncertainty ~ 1% Systematic -Placement of angle ~.5 o -Huge change in calibration constant ~5% Final result: M = 475 +/ 31 keV

14. Conclusion Substantial uncertainty Known value does lie within uncertainty Cross sections agree with quantum/ relativistic predictions Confirms particle properties of light Should be done in one day to minimize changes in calibration constant