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AGATA Collaboration(Akkoyun, S. et al), Algora, A., Barrientos, D., Domingo-Pardo, C., Egea, F. J., Gadea, A., et al. (2012). AGATA-Advanced GAmma Tracking Array. Nucl. Instrum. Methods Phys. Res. A, 668, 26–58.
Abstract: The Advanced GAmma Tracking Array (AGATA) is a European project to develop and operate the next generation gamma-ray spectrometer. AGATA is based on the technique of gamma-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 gamma 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 gamma-ray tracking 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.
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AGATA Collaboration(Avigo, R. et al), Domingo-Pardo, C., Gadea, A., & Gonzalez, V. (2020). Low-lying electric dipole gamma-continuum for the unstable Fe-62(,)64 nuclei: Strength evolution with neutron number. Phys. Lett. B, 811, 135951–6pp.
Abstract: The gamma-ray emission from the nuclei Fe-62,Fe-64 following Coulomb excitation at bombarding energy of 400-440 AMeV was measured with special focus on E1 transitions in the energy region 4-8 MeV. The unstable neutron-rich nuclei Fe-62,Fe-64 were produced at the FAIR-GSI laboratories and selected with the FRS spectrometer. The gamma decay was detected with AGATA. From the measured gamma-ray spectra the summed E1 strength is extracted and compared to microscopic quasi-particle phonon model calculations. The trend of the E1 strength with increasing neutron number is found to be fairly well reproduced with calculations that assume a rather complex structure of the 1(-) states (three-phonon states) inducing a strong fragmentation of the E1 nuclear response below the neutron binding energy.
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AGATA Collaboration(Cederwall, B. et al), Gadea, A., Jurado, M., Domingo-Pardo, C., Huyuk, T., & Perez-Vidal, R. M. (2020). Isospin Properties of Nuclear Pair Correlations from the Level Structure of the Self-Conjugate Nucleus Ru-88. Phys. Rev. Lett., 124(6), 062501–6pp.
Abstract: The low-lying energy spectrum of the extremely neutron-deficient self-conjugate (N = Z) nuclide Ru-88(44)44 has been measured using the combination of the Advanced Gamma Tracking Array (AGATA) spectrometer, the NEDA and Neutron Wall neutron detector arrays, and the DIAMANT charged particle detector array. Excited states in Ru-88 were populated via the Fe-54(Ar-36, 2n gamma)Ru-88* fusion-evaporation reaction at the Grand Accelerateur National d'Ions Lourds (GANIL) accelerator complex. The observed gamma-ray cascade is assigned to Ru-88 using clean prompt gamma-gamma-2-neutron coincidences in anticoincidence with the detection of charged particles, confirming and extending the previously assigned sequence of low-lying excited states. It is consistent with a moderately deformed rotating system exhibiting a band crossing at a rotational frequency that is significantly higher than standard theoretical predictions with isovector pairing, as well as observations in neighboring N > Z nuclides. The direct observation of such a “delayed” rotational alignment in a deformed N = Z nucleus is in agreement with theoretical predictions related to the presence of strong isoscalar neutron-proton pair correlations.
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AGATA Collaboration(Clement, E. et al), Domingo-Pardo, C., Gadea, A., Perez-Vidal, R. M., & Civera, J. V. (2017). Conceptual design of the AGATA 1 pi array at GANIL. Nucl. Instrum. Methods Phys. Res. A, 855, 1–12.
Abstract: The Advanced GAmma Tracking Array (AGATA) has been installed at the GANIL facility, Caen-France. This setup exploits the stable and radioactive heavy-ions beams delivered by the cyclotron accelerator complex of GANIL. Additionally, it benefits from a large palette of ancillary detectors and spectrometers to address in-beam gamma-ray spectroscopy of exotic nuclei. The set-up has been designed to couple AGATA with a magnetic spectrometer, charged-particle and neutron detectors, scintillators for the detection of high-energy gamma rays and other devices such as a plunger to measure nuclear lifetimes. In this paper, the design and the mechanical characteristics of the set-up are described. Based on simulations, expected performances of the AGATA l pi array are presented.
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AGATA Collaboration(Goldkuhle, A. et al), Perez-Vidal, R. M., Domingo-Pardo, C., & Gadea, A. (2019). Lifetime measurements in Ti-52,Ti-54 to study shell evolution toward N=32. Phys. Rev. C, 100(5), 054317–12pp.
Abstract: Lifetimes of the excited states in the neutron-rich Ti-52,Ti-54 nuclei, produced in a multinucleon-transfer reaction, were measured by employing the Cologne plunger device and the recoil-distance Doppler-shift method. The experiment was performed at the Grand Accelerateur National d'Ions Lourds facility by using the Advanced Gamma Tracking Array for the gamma-ray detection, coupled to the large-acceptance variable mode spectrometer for an event-by-event particle identification. A comparison between the transition probabilities obtained from the measured lifetimes of the 2(1)(+) to 8(1)(+) yrast states in Ti-52,Ti-54 and that from the shell-model calculations based on the well-established GXPF1A, GXPF1B, and KB3G fp shell interactions support the N = 32 subshell closure. The B(E2) values for Ti-52 determined in this work are in disagreement with the known data, but are consistent with the predictions of the shell-model calculations and reduce the previously observed pronounced staggering across the even-even titanium isotopes.
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AGATA Collaboration(Lalovic, N. et al), Gadea, A., & Domingo-Pardo, C. (2018). Study of isomeric states in Pb-198, Pb-200, Pb-202, Pb-206 and Hg-206 populated in fragmentation reactions. J. Phys. G, 45(3), 035105–27pp.
Abstract: Isomeric states in isotopes in the vicinity of doubly-magic Pb-208 were populated following reactions of a relativistic Pb-208 primary beam impinging on a Be-9 fragmentation target. Secondary beams of Pb-198,Pb-200,Pb-202,Pb-206 and Hg-206 were isotopically separated and implanted in a passive stopper positioned in the focal plane of the GSI Fragment Separator. Delayed gamma rays were detected with the Advanced Gamma Tracking Array (AGATA). Decay schemes were reevaluated and interpreted with shell-model calculations. The momentum-dependent population of isomeric states in the two-nucleon hole nuclei Pb-206/Hg-206 was found to differ from the population of multi neutron-hole isomeric states in Pb-198,Pb-200,Pb-202.
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AGATA Collaboration(Liu, X. et al), Gadea, A., Jurado, M., Domingo-Pardo, C., Huyuk, T., & Perez-Vidal, R. M. (2022). Evidence for spherical-oblate shape coexistence in Tc-87. Phys. Rev. C, 106(3), 034304–6pp.
Abstract: Excited states in the neutron-deficient nucleus Tc-87 have been studied via the fusion-evaporation reaction 54Fe(36Ar, 2n1p) Tc-87 at 115 MeV beam energy. The AGATA gamma-ray spectrometer coupled to the DIAMANT, NEDA, and Neutron Wall detector arrays for light-particle detection was used to measure the prompt coincidence of gamma rays and light particles. Six transitions from the deexcitation of excited states belonging to a new band in Tc-87 were identified by comparing gamma-ray intensities in the spectra gated under different reaction channel selection conditions. The constructed level structure was compared with the shell model and total Routhian surface calculations. The results indicate that the new band structure in 87Tc is built on a spherical configuration, which is different from that assigned to the previously identified oblate yrast rotational band.
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AGATA Collaboration(Liu, X. et al), Gadea, A., Jurado, M., Domingo-Pardo, C., Huyuk, T., & Perez-Vidal, R. M. (2021). Evidence for enhanced neutron-proton correlations from the level structure of the N = Z+1 nucleus Tc-87(43)44. Phys. Rev. C, 104(2), L021302–5pp.
Abstract: The low-lying excited states in the neutron-deficient N = Z + 1 nucleus (87)(43)Tcc(44) have been studied via the fusion-evaporation reaction Fe-54(Ar-36, 2n1p)Tc-87 at the Grand Accelerateur National d'Ions Lourds (GANIL), France. The AGATA spectrometer was used in conjunction with the auxiliary NEDA, Neutron Wall, and DIAMANT detector arrays to measure coincident prompt gamma rays, neutrons, and charged particles emitted in the reaction. A level scheme of Tc-87 from the (9/2(g.s.)(+)) state to the (33/2(1)(+)) state was established based on six mutually coincident gamma-ray transitions. The constructed level structure exhibits a rotational behavior with a sharp backbending at (h) over bar omega approximate to 0.50 MeV. A decrease in alignment frequency and increase in alignment sharpness in the odd-mass isotonic chains around N = 44 is proposed as an effect of the enhanced isoscalar neutron-proton interactions in odd-mass nuclei when approaching the N = Z line.
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AGATA Collaboration(Siciliano, M. et al), Gadea, A., Perez-Vidal, R. M., & Domingo-Pardo, C. (2020). Pairing-quadrupole interplay in the neutron-deficient tin nuclei: First lifetime measurements of low-lying states in Sn-106,Sn-108. Phys. Lett. B, 806, 135474–7pp.
Abstract: The lifetimes of the low-lying excited states 2(+) and 4(+) have been directly measured in the neutron-deficient Sn-106,Sn-108 isotopes. The nuclei were populated via a deep-inelastic reaction and the lifetime measurement was performed employing a differential plunger device. The emitted gamma rays were detected by the AGATA array, while the reaction products were uniquely identified by the VAMOS++ magnetic spectrometer. Large-Scale Shell-Model calculations with realistic forces indicate that, independently of the pairing content of the interaction, the quadrupole force is dominant in the B(E2; 2(1)(+) -> 0(g.s)(+)) values and it describes well the experimental pattern for Sn104-114 ; the B(E2;(+)(4) -> 2(1)(+)) values, measured here for the first time, depend critically on a delicate pairing-quadrupole balance, disclosed by the very precise results in Sn-108.
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AGATA Collaboration, Domingo-Pardo, C., Bazzacco, D., Doornenbal, P., Farnea, E., Gadea, A., et al. (2012). Conceptual design and performance study for the first implementation of AGATA at the in-flight RIB facility of GSI. Nucl. Instrum. Methods Phys. Res. A, 694, 297–312.
Abstract: The main objective of the Advanced GAmma Tracking Array (AGATA) is the investigation of the structure of exotic nuclei at the new generation of RIB facilities. As part of the preparatory phase for FAIR-NUSTAR, AGATA is going to be installed at the FRS fragmentation facility of the GSI centre for an experimental campaign to be performed in 2012 and 2013. Owing to its gamma-ray tracking capabilities and the envisaged enhancement in resolving power, a series of in-flight gamma-ray spectroscopy experiments are being planned. The present work describes the conceptual design of this first implementation of AGATA at GSI-FRS, and provides information about the expected performance figures. According to the characteristics of each particular experiment, it is foreseen that the target-array distance is adjusted in order to achieve the optimum compromise between detection efficiency and energy resolution, or to cover an specific angular range of the emitted electromagnetic radiation. Thus, a comprehensive Monte Carlo study of the detection sensitivity in terms of photopeak efficiency, resolution and peak-to-total ratio, as a function of the target-array distance is presented. Several configurations have been investigated, and MC-calculations indicate that a remarkable enhancement in resolving power can be achieved when double-cluster AGATA detectors are developed and implemented. Several experimental effects are also investigated. This concerns the impact of passive materials between the target and the array, the angular distribution of the detection efficiency and the influence of target thickness effects and transition lifetimes in the attainable detection sensitivity. A short overview on half-life measurements via lineshape effects utilizing AGATA is also presented. (C) 2012 Elsevier B.V. All rights reserved.
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