A LARGE-VOLUME, COAXIAL, LITHIUM-DRIFT, GERMANIUM GAMMA-RAY SPECTROMETER

Abstract

A high-resolution, germanium p-i-n diode gamma-ray spectrometer has been made using the coaxial method of lithium drift. The detector described is ~ 16 cm 3 in sensitive volume, three to four times that of the largest "planar" drifted diodes of this type described to date. Its performance as a spectrometer is comparable with that of smaller diodes; resolutions (fwhm) of 3.3 and 4.8 keV were obtained at γ-ray energies of 122 and 1 333 keV respectively with a detector bias of 1 000 to 1 500 V. Typical γ-ray spectra obtained with sources of 57 Co, 60 Co, 137 Cs, and Th(B + C + C″) are shown. Also shown are curves of intrinsic full-energy peak efficiency over a range of energies. This efficiency is 2.5% at 1 300-keV γ-ray energy—comparable to that of a NaI scintillation spectrometer 1 in. in diameter by 1 in. long.