Study of low lying levels of 72Ni

The nuclear shell model has been proven to be very successful in explaining different properties of stable isotopes. In this model, nucleons inside the nucleus are arranged in discrete energy levels. Large gaps between the levels are interpreted as closed shells and give rise to the magic numbers 2, 8, 20, 28, 50, 82 and 126, which characterize more stable nuclei. However, it has been found that when going away from the valley of beta-stability, towards more exotic isotopes, the arrangements of the energy levels can change. Such modifications cause the appearance of new magic numbers as well as the disappearance of some of them and this behaviour is called shell evolution. Models to explain these changes have been proposed, pointing at the role of the residual interactions between nucleons. A particularly interesting region of the nuclear chart to study shell evolution is among the neutron-rich nickel isotopes. For these isotopes, the conservation of the Z=28 shell gap has been suggested up to 78Ni. Data on low-lying states of a few of these very neutron-rich nuclei has been obtained using radioactive beams at the world leading facility for in-flight production of exotic nuclei, the Radioactive Isotope Beam Factory (Japan). In the present work, a spectroscopic analysis is performed on 72Ni, populated by reactions of proton knockout and neutron knockout, where the gamma-ray signals were detected by the DALI2 NaI-scintillator array. A Geant4 simulation software is used to obtain a realistic response of the detector, which is employed in the process of the fitting of the spectra. After identifying the transitions between excited states, a coincidence analysis is performed on the found gamma-rays and a level scheme of the isotope is constructed. The discussion of the results is aided by the comparison with shell model theoretical calculations.