Commissioning of the AGATA gamma-ray tracking array

The Advanced GAmma Tracking Array (AGATA) is a European project for a 4 pi new-generation gamma-ray tracking spectrometer. Thanks to the digital electronics, the traces of the single interactions of the photons are acquired to perform Pulse Shape Analysis (PSA) and localize the interaction points in the HPGe crystals with a precision up to 5 mm. Subsequently, the application of gamma-ray tracking algorithms can reconstruct the trajectories of the gamma rays within the detector. AGATA has performed a rich science program using both radioactive and stable ion beams in several European laboratories, coupled to different complementary detectors. In the second half of 2021, AGATA was installed at the Legnaro National Laboratories (LNL) and its experimental campaign started at the end of May 2022. Before the actual experimental campaign started, a series of commissioning experiments were planned to test both the AGATA array and the available complementary detectors. Such first tests are essential to verify the functioning of all the parts of the setup and evaluate the capabilities of the array in the new configuration with the most recent upgrades. The work in this master thesis focuses on the description and optimization of the processing of the AGATA data and the assessment of the detector performances both with gamma-ray sources and during the first in-beam commissioning experiment. All the preparatory stages for the operation of AGATA are introduced, from the electronics and the support systems for the detectors, to the sorting of the raw data. The data processing envisages different stages, starting by the local level processing that handles the crystals separately. Energy calibrations, time calibrations and cross-talk corrections are applied to ensure a good performance of the PSA. The PSA algorithm provides the position, energy and time of each interaction point of the gamma rays with accuracy for the tracking algorithm. Additionally, the PSA provides the information for the neutron damage correction for an improved energy resolution. Finally, a global level processing merges the information from the individual crystals and tracking is performed, combining multiple interactions to reconstruct a larger fraction of full-energy peak events. In this work, all the steps of the AGATA processing were examined and optimized up to the tracking reconstruction. The optimization was done by tuning a set of parameters that are obtained through measurements with radioactive sources. The output gamma-ray spectra of the sources were analyzed to assess the performances of AGATA in terms of energy resolution, efficiency and peak-to-total ratio. Simulations were also performed for the same radioactive sources and efficiency curves were compared for the measured and simulated data. Later, resolution and efficiency measurements have to be performed with the use of additional gamma-ray sources. In the thesis, the in-beam performances of the AGATA array in the first commissioning experiment were studied, where the detector was coupled to the PRISMA magnetic spectrometer. The studied reaction consisted of a multi-nucleon transfer with a 32S beam at 160 MeV on a 124Sn target. The different transfer channels were selected thanks to the A and Z identification in PRISMA and the gamma rays associated to the populated energy levels were observed in coincidence with AGATA after the Doppler correction of the photons emitted in flight. The Doppler-corrected spectra for the products of the -2p transfer channel, corresponding to the nuclei 30Si and 126Te, were analyzed and level schemes were constructed with the observed gamma rays.