The Advanced GAmma Tracking Array (AGATA) is a European project to develop and operate the next generation γ-ray spectrometer. AGATA is based on the technique of γ-ray energy tracking in electrically segmented high-purity germanium crystals. This technique requires the accurate determination of the energy, time and position of every interaction as a γ ray deposits its energy within the detector volume. Reconstruction of the full interaction path results in a detector with very high efficiency and excellent spectral response. The realisation of γ-raytracking and AGATA is a result of many technical advances. These include the development of encapsulated highly segmented germanium detectors assembled in a triple cluster detector cryostat, an electronics system with fast digital sampling and a data acquisition system to process the data at a high rate. The full characterisation of the crystals was measured and compared with detector-response simulations. This enabled pulse-shape analysis algorithms, to extract energy, time and position, to be employed. In addition, tracking algorithms for event reconstruction were developed. The first phase of AGATA is now complete and operational in its first physics campaign. In the future AGATA will be moved between laboratories in Europe and operated in a series of campaigns to take advantage of the different beams and facilities available to maximise its science output. The paper reviews all the achievements made in the AGATA project including all the necessary infrastructure to operate and support the spectrometer.
Key words: AGATA γ-Ray spectroscopy, γ-Ray tracking, HPG e detectors, Digital signal processing, Pulse-shape and γ-ray tracking algorithms, Semiconductor, detector performance and simulations.
The realisation of the AGATA spectrometer is a result of many technological advances. These range from advances in Ge detector technology, digital DAQ systems, signal decomposition and γ-ray interaction reconstruction, and in many areas of the infrastructure needed to support and operate such a complex device.
The AGATA spectrometer is now fully operational in its first physics campaign at INFN LNL in Legnaro, Italy, utilising the wide range of stable beams available. A view of AGATA at the target position of the PRISMA spectrometer is shown in Fig. 43. AGATA is designed to be a peripatetic instrument and will move between major laboratories in Europe to take advantage of the range of different beams and equipment at each laboratory and of the resulting scientific opportunities. AGATA will be operated in a series of campaigns, the one first at LNL, and subsequently at the GSI facility in Germany and the GANIL laboratory in France. At GSI, AGATA will be used at the exit of the Fragment Separator (FRS) to study very exotic nuclei produced following high-energy fragmentation and secondary Coulomb excitation. At GANIL it will use the wide range of radioactive ions from the coupled cyclotrons and SPIRAL. During these first three physics campaigns the array will continually increase its efficiency as more detector systems are added. The first stage is to build up the system to 60 detector crystals, and then proceed towards the full implementation of the 4π AGATA. Subsequent physics campaigns will take advantage of the new radioactive beams available as facilities such as FAIR, SPIRAL2, SPES and HIE-ISOLDE come online.
AGATA will have an enormous impact on nuclear physics research in particular the exploration of nuclear structure at the extremes of isospin, mass, angular momentum, excitation energy, and temperature. This radically new device will constitute a dramatic advance in γ-ray detection sensitivity that will enable the discovery of new phenomena in nuclei, which are only populated in a tiny fraction of the total reaction cross-section or that are only produced with rates of the order of a few per second or less. The unprecedented angular resolution afforded by its position sensitivity will facilitate high-resolution spectroscopy with fast and ultra-fast fragmented beams giving access to the detailed structure of the most exotic nuclei that can be reached. In addition, the capability to operate at much higher event rates will allow the array to be operated for reactions with intense γ-raybackgrounds.
The instrumentation and technical advances driven by this work, and the knowledge gained by those involved, are also important in a wide range of applications. These advances have potential impact in areas such as medical imaging systems, homeland security, environmental monitoring and the nuclear industry.
In addition to the technical advances, AGATA represents a tremendous human achievement in the successful collaboration of several hundred personnel in 12 countries and over 40 laboratories and institutes across Europe. The collaboration is now excited with the prospect of using this spectrometer and to capitalise on its discovery potential for the understanding of the atomic nucleus.
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