Advances in nuclear structure via charged particle reactions with AGATA

International audienceIn recent decades, $\gamma $-ray spectroscopy has undergone a major technological leap forward, namely the technique of $\gamma $-ray tracking, and has attained a sensitivity that is two orders of magnitude larger than that provided by the former generation of Compton-shielded arrays. Indeed the gain is comparable with the achievements since the dawn of $\gamma $-ray spectroscopy. Such sensitivity can be further heightened by coupling $\gamma $-ray spectrometers to other detectors that record complementary reaction products such as light-charged particles for transfer reactions and scattered ions for Coulomb excitation measurements. Nucleon transfer reactions offer an excellent mean to probe the energies of shell model single-particle orbitals and to study migration in energy of these orbitals as we venture away from stability. Such measurements can also estimate the cross sections of processes relevant to stellar evolution and nucleosynthesis. The measurement of $\gamma $ rays in coincidence with particles provides also information on the decay channel for unbound systems, which constitutes a useful input for astrophysics and nuclear structure near the drip-lines. Coulomb-excitation studies make it possible to infer collective structure in nuclei and to extract deformation properties of, in particular, open-shell systems. Here, selected examples will be presented, highlighting the power of these types of experiments when $\gamma $-ray observation is included. The development of the experimental methods is reviewed, showing the results achieved before the advent of $\gamma $-ray tracking. Examples of more recent experiments that have successfully exploited $\gamma $-ray tracking with AGATA are then presented as showcases for the outstanding performance of the composite detection systems. The outlook for experiments using newly developed devices such as GRIT and other detectors such as SPIDER is described