Encapsulated germanium γ-ray spectrometers performance characteristics and operational experience

Abstract
Hermetically sealed Ge(Li) diodes for γ-ray spectroscopy have now been manufactured and under study for approximately two years. During this time, 'planar' drifted encapsulated diodes have been increased in size from 2 cm2 × 2 mm deep (0.4 cm3) to ˜ 8 cm2 × 10 mm deep (8 cm3). Coaxially drifted diodes of 25 to 30 cm3 volume have also been encapsulated. Encapsulation details of both types of detector are given, together with performance characteristics. Measured intrinsic full-energy peak efficiency curves are given for four detector sizes. For an 8 cm3 planar diode this efficiency is 1.1% at 7 cm for 1 MeV γ-rays. The corresponding efficiency for a 27 cm3 coaxial diode is 3.1%. Voltage ratings of 1000 V/cm with leakage currents ⩽ 1 nA at operating voltage are achieved. Resolutions of 3.4 and 5.5 keV (fwhm) at 1173 keV γ-ray energy have been obtained with a 2 cm3 (5 mm deep) planar diode and a 27 cm3 coaxial detector respectively. Mounting and general application details are discussed.