From Ge(Li) detectors to gamma-ray tracking arrays–50 years of gamma spectroscopy with germanium detectors

The structure of the atomic nucleus has been studied to a large extent by gamma-ray spectroscopy using germanium (Ge) detectors. Ge detectors were developed in the 1960s and still offer the best compromise between energy resolution and efficiency for high-resolution gamma-ray spectroscopy. In the 1970s and 1980s the main advances were in the purity and volume of the Ge crystals. More recently the development of highly-segmented Ge detectors has significantly increased the performance and power of detection systems. In a segmented Ge detector the crystal is divided into sections by isolating the contacts. This enables the position of interaction to be determined. The accuracy of the position determination can be improved by the analysis of the shape of the charge signals and of the transient signals in adjacent segments. This technique has led to the concept of gamma-ray tracking in a segmented Ge detector whereby the energy, time and position of all interactions are recorded and the full interaction is reconstructed. This enables a spectrometer system with unprecedented efficiency and energy resolution to be realized. In this article, the history of Ge detectors and Ge detector arrays for nuclear spectroscopy will be reviewed. The technology and properties of highly-segmented coaxial Ge detectors as developed for the European γ -ray tracking array AGATA will be highlighted.