Encapsulated germanium γ-ray spectrometers performance characteristics and operational experience

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.