A BASISFOR CALCULATINGEXPECTED DETECTOR EFFICIENCY

A methodispresented wherebytheintrinsic efficiency ofGe isutilized tocalculate theexpected peakefficiency ofdetectors havinga widerange of sizes.Theintrinsic efficiency ofGe,whichis the probability fortotal absorption, was measured at122 and136keVinGe(Li) coaxial detectors andHPGe planar detectors having an effective thickness ranging from5 to50mm. At136keVitis64%fora thickness of10mm and82%for20mm, after whichitlevelsoff reaching 89%at50mm. Itis shownthatthepeakefficiency ofa detector isa product ofonlytheintrinsic efficiency andthesolid angle, once lossesduetoedge escape anddetector imperfections (surface channels andhighdislocation densities) aredetermined. The absolute andrelative [toNaI(Tl)] peakefficiency ofa sampledetector, calculated on thebasisofintrinsic efficiency, are ingoodagreementwithmeasured values. Thismethodshould findapplications inthedesignof new detector systemsparticularly thosefordiagnostic imaging with"Tc(140keV).