EPJ A Highlight - Germanium detectors get position sensitive

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Published on 21 June 2016

High purity germanium detectors have grown into the most popular devices within the field of gamma ray spectroscopy. The sensitive part of these detectors consist of the largest, purest and monocrystalline semi-conductors used on earth. In the past Ge, detectors were famous for their outstanding energy resolution and timing information for electromagnetic radiation, especially in the field of nuclear physics and nuclear astrophysics. Recently the introduction of digital data acquisition systems and the segmentation of the Ge crystals opened up new opportunities. The interaction position of the gamma rays inside the detector volume provides new additional information by means of the pulse shape of the various signals. In this way, the Ge detector becomes a position sensitive device and allows for a novel detection method called gamma-ray tracking.

New gamma ray spectrometers are currently under construction and implement the new method. The pulse shape analysis technique requires a very precise understanding of all detector properties and the article describes all the theoretical concepts. Moreover, detailed numerical calculations are performed to create a huge set of hundred thousands of detector pulses. These pulses are compared to measured pulses from individual gamma rays in order to extract the position where the radiation interacted with the detector material. A new and elaborate computer code, named ADL, was developed for this purpose. ADL utilizes all relevant aspects of signal creation and formation with the Ge detector and the subsequent electronics. Meanwhile the code is successfully implemented and used for position sensitive gamma-ray spectroscopy within the AGATA project.