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978-3-8439-0179-6, Reihe Physik

Andreas Wiens
Optimized high energy resolution in γ-ray spectroscopy with AGATA triple cluster detectors

123 Seiten, Dissertation Universität Köln (2011), Softcover, A5

Zusammenfassung / Abstract

The AGATA demonstrator consists of five AGATA Triple Cluster (ATC) detectors. Each triple cluster detector contains three asymmetric, 36-fold segmented, encapsulated high purity germanium detectors. The purpose of the demonstrator is to show the feasibility of position-dependent g-ray detection by means of g-ray tracking, which is based on pulse shape analysis. The thesis describes the first optimization procedure of the first triple cluster detectors. The signal quality was optimized and the energy resolution was improved through the modification of the electronic properties, of the grounding scheme of the detector in particular.

The first part of the work was the successful installation of the first four triple cluster detectors at INFN in Legnaro, Italy, in the demonstrator frame. The four ATC detectors combine 444 high resolution spectroscopy channels.

In the second part of the work new methods for enhanced energy resolution in highly segmented and position sensitive detectors were developed. The signal-to-noise ratio was improved through averaging of the core and the segment signals, which led to an improvement of the energy resolution of 21 % for g-energies of 60 keV to a FWHM of 870 eV. In combination with crosstalk correction, a clearly improved energy resolution was achieved for events of each hit-segment multiplicity. For g-ray energies of 1.33 MeV, an improvement of 20% was achieved.

The study of electron trapping using a new position-sensitive correction method for the energy measurement was completed.

The correction of electron trapping resulted in an additional improvement of the full width at half maximum of the peaks of the $\gamma$-spectra. A total energy resolution of $\unit[2.01]{keV}$ at $\unit[1.33]{MeV}$ was achieved with a segmented, large volume germanium detector. The position-sensitive operation enabled calculating the Fano factor, which resulted in $F=0.095\pm 0.005$. Eventually, a significant improvement of the energy resolution was achieved. Consequently, the novel segmented high-purity germanium AGATA detectors are operated at significantly improved conditions superior to the common Ge detectors in energy and position resolution. The essential improvement arises from the redundant energy measurement of independent core and segment electrodes and from the correction of the position-dependent trapping effects.