Polarization of Gamma Rays Using Compton Scattering

1
Polarization of Gamma Rays Using Compton
Scattering

• Midn 2/c Tim Fitzgerald
• Advised by Dr. Daryl Hartley
• 2 May 2005

Sponsored by the National Science Foundation
2
Introduction

• Purpose
• Want to determine characteristics of excited
  nuclear states
• Show that types of gamma rays
• can have either electric or
• magnetic nature
• Method
• Excite nuclei of Mg-24 and Mg-25
• using proton beam
• Collect gamma rays with detector
• Analyze results

3
The Experiment

• NATALY
• 2.5 MeV incident protons
• Data collected for 28 min
• (approx. 16 billion particles)
• Detector
• Clover Detector
• Four separate Ge crystals
• 2-D spatial resolution

4
The Experiment

• Protons excite nucleus

5
The Experiment

• Excited nucleus emits gamma ray

6
The Experiment

• Gamma Ray hits detector

7
The Experiment

• Gamma ray hits detector
• Ray will excite electrons in crystal
• Electrons will be pulled off by bias voltage
• Compton scattering
• Rays can scatter after first incident into
  another crystal
• Detector sees two incidents in same coincidence
  window
• Total energy of original gamma ray found by
  summing the energies seen in the two crystals
• Analysis will determine the direction of scatter
• Magnetic vs. Electric
• If scatter is perpendicular to reaction plane,
  gamma is electric
• If scatter is parallel, it is magnetic

8
Results

• Perpendicular Scatter

9
Results

• Parallel Scatter

10
Results

• Difference in spectra

-.18
.56
13.32
11
Results

• What does this graph tell us?
• Change in height of peaks shows bias
• V counts of perpendicular scatters in peak
• H counts of parallel scatters
• A gt 0 means electric
• A lt 0 means magnetic
• Discussion of Result
• Found Strong E2 peak
• Found mixed M1/E2 peak
• Found mixed E2/M3 peak
• New lab for SP434