Doppler Broadening Spectroscopy:

1
Doppler BroadeningSpectroscopy
Analysis of Rubber Composites

• Chun Yang
• Mentor Dr. C.A. Quarles

2
Initial Goal

• To confirm non-uniformity found in rubber samples
  by V.O. Jobando and John Rhoads from previous
  Lifetime Analysis work.
• Composite rubber used in industry are possibly
  not homogeneous.
• Positron Annihilation Spectroscopy could be used
  to find non-uniformities in mixed rubber.
• Doppler Broadening was chosen in particular for
  better analysis of composition differences.

3
Some Background

• Doppler Broadening PAS involves the momentum
  distribution of electrons annihilated with
  positrons.
• Greater momentums of annihilation increase
  Doppler shift in the signal of the photon energy
  released.
• Para-positronium formed have a very low momentum
  of annihilation.
• Increasing carbon will decrease positronium
  formation.
• Fewer low-momentum distributions.
• DB signals directly related to uniformity.

4
Unexpected Challenges
5
Overcome!

• S-Parameter fluctuation appeared to be related to
  dead time.

6
Rate Dependency

• Dead Time is affected by both the number of
  channels counted and counting rate.
• The number of channels counted is dependent on
  the MCA card settting.

• Counting rate, which is dependent on the
  amplifier settings, is directly affected by the
  distance of the sample from the detector.

7
Once Again

• Reexamined SnSSBR rubber with a reasonably stable
  counting rate.

8
Uniformity Data

• Rubber with differing phr (parts per hundred
  rubber) of N774 carbon black analyzed.

9
Concentration Data

• Analysis conducted on N774 and N115 samples.
• Concentration of Carbon Black affects S-parameter.

10
Looking Ahead

• Technique Refinement
• Metal Covering
• Consider Temperature
• Look for non-uniformity based on mixing time.
• Possible application for faster material analysis
  due to rate dependence.

11
Acknowledgements

• I would like to thank
• The NSF for providing the funding for this
  program (and paying me).
• The TCU Department of Physics and Astronomy for
  their support.
• Dr. C.A. Quarles for guiding me on this project.