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EXOGAM detector characterisation

The EXOGAM Clover detectors will be used with digital electronics to allow the use of Pulse Shape Analysis (PSA) techniques to aid the identification of the interaction position of incident gamma-ray photons. The Liverpool group in collaboration with the EXOGAM collaboration is leading the characterisation of the detector response function in order to allow position information to be derived from the detector preamplifier signals.

The Liverpool automated scanning table and digital electronics system has been used to calibrate the response of the Ortec EXOGAM Clover detectors utilising both singles and coincidence measurements.

The picture (above right) shows the intensity as a function of position for 662 keV photons incident on a Clover detector. The data was collected using a 2mm collimator and 5 minutes acquisition at each position. The image was produced from the data by demanding all the energy is deposited inside a outer contact segment. The effective segmentation of the detector is clearly visible.

The rise time response of a detector is shown in the figure (left) . The observed range of rise times is 100-220ns. The picture shows the crystallographic lattice orientation of the germanium FFC crystals. A specification of the EXOGAM detector is that the lattice orientation should be aligned in all four crystals and that the 100 axis is aligned for maximum rise time differences (as shown).