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Positron-Electron Creation\Annihilation

LEVEL 3 LABORATORY

High Energy Physics

High Resolution Gamma-ray Spectroscopy: e+-e– creation/annihilation

Objectives of the Project

  • Become familiar with the characteristics of a coaxial solid state Germanium (Ge) detector.
  • Investigate the spectra of gamma rays transmitted by various materials to determine how the efficiency of e+-e– pair creation varies with atomic number.


Apparatus

  • Elemental samples.
  • Coaxial Ge detector.
  • High voltage supply.
  • Electronics: Spectroscopy amplifier, Multi-channel Analyser (MCA).

Experimental Procedure

  1. Measure the efficiency of the detector as a function of gamma-ray energy at the recommended operating voltage of the detector.
  2. Measure the resolution of the detector as a function of gamma-ray energy at the recommended operating voltage of the detector.
  3. At a gamma-ray energy of 0.662 MeV, determine the efficiency and resolution of the detector for various applied voltages up to the recommended operating voltage. What area of the detector is functioning at low applied voltages?
  4. Study the spectral energy distributions of several radioactive sources, e.g. Na22, Cs137, Co60.
  5. Measure the gamma-ray background with the detector inside and outside the lead shielding. Identify any lines in the background spectrum.
  6. Modify the experimental setup so that solid materials (targets) may be placed between the source and the detector. Measure the gamma ray spectra to investigate the variation of e+-e– creation/annihilation as a function of the atomic number of the target and as a function of initial gamma ray energy.

Safety and Precautions

The gamma ray emitting sources (e.g. Co60, Cs137 and Na22) must only be handled using the tweezers that are provided.


References

  • Knoll, G.F: Radiation Detection and Measurement.
  • Leo W.R.: Techniques for Nuclear and Particle Physics Experiments
  • Useful statistics


Useful Links