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Spectroscopy of exotic nuclei in a Magnetic Active Target

Final Report Summary - SPECMAT (Spectroscopy of exotic nuclei in a Magnetic Active Target)

Our knowledge about the nuclei at the centre of atoms was based for a long time on the information collected on the few stable nuclei existing in nature. In recent years, however, nuclei far from stability (with an excess of protons or neutrons) have become accessible at large accelerator facilities. Their study has revealed truly exotic properties (unexpected shapes, new decay modes, and others) that challenge our understanding of their structure and dynamics.

The SpecMAT project aims at providing crucial experimental information to answer key questions about the properties of the nuclei.
Nucleon-transfer reactions have proven to be a reliable probe for these studies. With SpecMAT, a novel instrument was realised, which overcomes the present challenges in performing such measurements with very weak beams of unstable nuclei. It combines the high luminosity, high efficiency and large dynamic range of an active-target detector (a gaseous detector where the detection gas is also the target of the nuclear collisions), with the detection of gamma-ray radiation in a compact array of scintillation detectors. The instrument will be placed in the magnetic field of a solenoidal magnet, to identify the charged particles emitted in the reaction through their cyclotron motion. The SpecMAT detector will be coupled to the HIE-ISOLDE facility for the production and post-acceleration of radioactive ion beams at CERN in Geneva.

The novel active target technology, developed in parallel for SpecMAT and other active-target detectors in Europe, was employed in measurements at the LNS (Catania, Italy) and GANIL (Caen, France) facilities. The measurements aimed at the clarification of the interplay between deformation and isoscalar strengths in light nuclei (20Ne, at LNS) and the precise determination of the isoscalar resonances in the unstable 68Ni nucleus (at GANIL). Preliminary results show an improvement of a factor 3-4 in the energy resolution of the latter measurement, which will impact the constraints on the value of the incompressibility of nuclear matter.