The activity of the gamma spectroscopy group in Milano is devoted to the study of nuclear structure, having the gamma spectroscopy as main tool and focus. This research is set within the framework of wide international collaborations. Main topic is the study of shell structure and collective modes in both stable and exotic systems, exploiting different reaction mechanisms and decay modes. The experimental activity is based on the use of multi-detector arrays at stable and radioactive ion beam facilities. Our group is involved in detector R&D, in particular related to new scintillator materials and associated electronics.
Shell structure and warm rotation
The investigation of shell structure and collective excitations of nuclei far from the stability line has become a key topic of nuclear structure in recent years. Many experiments have been performed to measure observables, such as energy, spin and lifetimes, to constrain the shell model in such systems. Interesting results have been recently obtained in nuclei pointing to the presence of excited states as due to particle-vibration coupling. Moreover, the thermal response of nuclear systems at high excitation energy above the yrast line can be studied experimentally through the analysis of quasi-continuum spectra, providing information on the order-to-chaos transition undertaken by the nucleus at increasing temperature.
Giant resonances are collective excitations involving a large number of nucleons. They can be considered as a good testing ground to study basic properties of nuclear systems. As an example, detailed measurements of mirror nuclei to determine the isospin symmetry and isospin mixing in nuclear states are under analysis. Furthermone, in recent years many experiments have been performed at Laboratori Nazionali di Legnaro, GSI, Riken etc. to study the properties of resonances in exotic systems, where new modes of excitation have been observed, as the pigmy dipole resonance.
Deep-inelastic and multi-nucleon transfer reactions have been largely used in the past to study heavy systems, as a complementary tool to fusion-evaporation reactions to populate high-spin states in particular in neutron-rich systems. In this respect a series of experiments is being proposed at Laboratori Nazionali di Legnaro, Ganil, Isolde etc., employing both stable and radioactive beams. The aim of this campaign is to investigate the reaction mechanism itself and to perform γ-spectroscopy studies towards the neutron drip-line.
Beta decay studies of nuclei far from stability are an important tool to access first fundamental information such as the half-life and decay modes in the parent nucleus, and to get an insight in the structure of the daughter nucleus. The evaluation of half-lives is strictly related to the description of stellar nucleosynthesis, since they define the paths and waiting points of the processes involved.
The detector R&D is related to the characterization of phoswich detectors and of new scintillator materials, such as LaBr3:Ce, CLYC, GAGG, and GYGAG, used for the detection of both γ-rays and neutrons. The associated electronics and the data acquisition system are specifically designed, in Milan, for our large volume LaBr3:Ce detectors and for the phoswichs. The detector R&D activity addresses also the development of technology for γ-imaging, aimed at obtaining the interaction points of γ-rays inside a large volume scintillator crystal.