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Simone Ceruti, who graduated at the Department of Physics of Milano University has been awarded the 2016 Claudio Villi prize for the best Ph.D. Thesis in nuclear physics in Italy. The Ph.D thesis work, done in collaboration with the INFN section of MIlano, concerns the isospin symmetry violation and was supervised by Prof. Franco Camera.

The isospin symmetry is associated with the charge independence of the strong force.  This symmetry is violated in nuclei by the Coulomb force, so that  isospin is a good quantum number only to a first approximation.  It is important to have a reliable and quantitative estimates of the amount of isospin violation. This affects properties like the lifetime for superallowed Fermi beta decays and the coupling term between u- and d- quarks  in the Cabibbo-Kobayashi-Maskawa matrix.

Nuclear spectroscopy techniques can provide unique information on these quantities, as was demonstrated in Simone Ceruti’s thesis work. Ceruti studied the mixing between states of different isospin looking at its effects on dipole electromagnetic transitions.

Ceruti studied the giant dipole resonance gamma decay in the excited nucleus ⁸⁰Zr. The nucleus was produced by the fusion of two ⁴⁰Ca ions at the INFN Legnaro laboratories. Scintillator detectors (LaBr3:Ce) and  segmented Germanium detectors of the multi detector AGATA (Advanced Gamma Tracking Array) have been used to measure  low (≈1 MeV)  and high  (> 10 MeV)  gamma rays respectively.

An advanced statistical model analysis was carried out on the experimental data, in order to determine the value of the isospin mixing probability α² as well as the isospin term δ_c correcting the lifetime for Fermi decay in ⁸⁰Zr, at a temperature of about 2 MeV. From the latter, and using reliable theoretical models, it is then possible to deduce the value of  δ_c of ⁸⁰Zr in the ground state (δ_c = 0.81% ± 0.16%).