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Compton Scattering: Observation of the Compton wavelength shift

Tony Hyun Kim (Partner: Connor McEntee) 12/1/2008 8.13 MW2-5 Prof. Roland. Compton Scattering: Observation of the Compton wavelength shift. Topics to be discussed. Introduction Classical EM vs. Compton scattering Compton wavelength shift Compton scattering (Klein- Nishina ) cross-section

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Compton Scattering: Observation of the Compton wavelength shift

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  1. Tony Hyun Kim (Partner: Connor McEntee) 12/1/2008 8.13 MW2-5 Prof. Roland Compton Scattering:Observation of the Compton wavelength shift

  2. Topics to be discussed • Introduction • Classical EM vs. Compton scattering • Compton wavelength shift • Compton scattering (Klein-Nishina) cross-section • Experimental setup • Compton A vs. Compton B • Analysis and Results • Fitting the lineshape • Measured Compton shifts • Conclusions • Observation of wavelength shift in light scattering

  3. Classical (Rayleigh) scattering • Scattering is dipole radiation from a driven dipole oscillator. • Governed by Maxwell’s equations. • Linear physics: frequency and wavelength are invariant. Image source: http://www.azonano.com/details.asp?ArticleID=1239

  4. Compton scattering • Modern picture of light: photons • Basic results of QM and relativity: E = hc/ λ ; p = h/λ • Usual conservation laws yield: Image source: http://commons.wikimedia.org/wiki/Image:Compton_scattering-de.svg

  5. Compton scattering • Modern picture of light: photons • Basic results of QM and relativity: E = hc/ λ ; p = h/λ • Usual conservation laws yield: Image source: http://commons.wikimedia.org/wiki/Image:Compton_scattering-de.svg

  6. Compton scattering cross-section

  7. Experimental setup (Compton A)

  8. Complications: Geometry Angular spread (FWHM) of the beam ~12°

  9. Complications: Electronic Arbitrary discriminator level w.r.t. Target PMT

  10. Comparisons between Compton A, B • Due to these complications, high-angle measurements are preferred. • Source in Compton B is 2.4 times more intense than Compton A. • Fatal flaw: Compton A does not yield signal beyond ~70° • Longer lever arm in Compton B: better angular specificity. (Approx. 12.5° vs. 20.8°)

  11. Typical MCA data (Scatter PMT 110°)

  12. Compton shift results • Low angle measurements underestimate the Compton shift, as predicted by geometry. • Compton A underestimates incident energy at E = 635keV. Possibly caused by the set-point complication.

  13. Compton shift results (cont.) • Wavelength variation observed  Rayleigh picture is inadequate. • Fit to Compton B yields: • Incident energy: • Electron rest mass: • Goodness of fit:

  14. Conclusions • Observed the wavelength shift in light scattering. Unexplained by classical scattering. • Obtained 4 large-angle data points on Compton B, showing good agreement to Compton shift formula. Fit yields: • Incident energy: • Electron rest mass:

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