Paralleling Planar Ge(Li) Detectors for Counting Large Volume Biological Samples

Four planar Ge(Li) detectors have been operated in an array, in parallel electrically, and connected to a single preamplifier. The total active volume is 28 cm3. The photopeak efficiency of the four detector array at 1.33 MeV is about 4.8 times greater than the efficiency of one 7 cm3 detector. The resolution is 2.90 keV FWHM at 1.33 MeV and 2.01 keV FWHM at 122 keV. Some misalignment of the individual detector photopeaks is observed, probably caused by contact resistance. A technique which allows alignment of the peaks is presented.