Germanium Shells

The most efficient gamma ray spectroscopy apparatus attempts to completely surround the nucleus under investigation, covering as much of the 4Ï€ solid angle as possible. Conventional Ge gamma ray detector arrays are usually surrounded by escape suppression shields. These shields detect and reject coincident events in the Ge detector which increases the ratio of counts in the full energy peaks to the total number of counts. Gamma ray tracking allows us to remove the escape suppression shields, giving us two advantages. Firstly the Germanium detectors are packed closely together, giving better coverage of the 4-pi area (escape suppression shields in a 4-pi array cover 50% of the solid angle). Secondly the gamma rays which scatter out of one detector can be tracked using others if the relative positions of the detectors are well defined. So the escaping Compton scattered gammas and 511keV pairs can now be measured rather than rejected with a consequent improvement in the peak to total counts ratio.

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