Compton Scattering

James DurginPhysics 521March 19, 2009

Background

Collecting energies at several points lets one find electron mass and cross section

Image from user-review.ca

Photomultiper tube

Scintillator

Lead shielding

Copper cylinder

Source inside shielding

Experimental Theory

Calibrate multichannel analyzer Collect energy spectrums with copper

cylinder Collect energy spectrums without copper

cylinder Fit points to find electron mass and

experimental cross section

Calibration

IsotopeFirst DecayEnergy

First Decay Percentage

Second DecayEnergy

Second Decay Percentage

Co-57 122.06 keV 85.60% 136.47 keV 10.60%

Co-60 1173.24 keV 100% 1332.50 keV 100%

Cs-137 661.66 keV 85.10%    

Ba-133 356.02 keV 62.10%    

Isotope energies v. channel number

Energy Spectrums

Counts per channel v. channel number Net counts v. channel number

Slope (inverse electron mass) 0.001985

95% interval (0.001928, 0.002043)

Y intercept 7.23E-05

95% interval (1.04e-05, 0.0001342)

Degrees of freedom 9

R2 0.9984

Electron mass 503.8 keV

Uncertainty ± 14.6 keV

Graphical Compton’s Equation

Net counts v. channel numberFit for Compton Scattered Photons

Cross section comparison

Collected data follows Klein-Nishina cross section

Thomson cross sectionThomson equation

Klein-Nishina cross sectionKlein-Nishina equation

Uncertainty Analysis

Statistical nature of counts Setup uncertainty Conversion uncertainty Negligible events

Conclusion

Experimental electron mass of 503.8 ± 14.6 keV v. actual electron mass of 510.998910±0.000013 keV

Collected data has closer agreement with Klein-Nishina model