Mesure de masses de noyaux dans la region N=Z=40

Abstract : Mass measurement of very proton-rich nuclei is a way to study nuclear pairing far from stability. In particular, N=Z nuclei present strong effects called Wigner effects. Determination of the residual interaction between the last proton and the last neutron, by measuring masses, leads to a better understanding of these characteristics and a test of spin-isospin SU(4) symmetry. In the region N=Z=[34;40] nuclei have also an astrophysical interest in the modelling of the rp process. The second cyclotron of GANIL -CSS2- has been used as a mass spectrometer of high resolution. Exotic nuclei were produced by a fusion-evaporation reaction between a 58Ni (4.3 MeV.A) beam and 24Mg and 12C targets. They are injected simultaneously with ions with well-known masses which constitute references for the measurement. Ions are time-separated as they are accelerated and their relative mass difference are linearly related to their relative difference of total time-of-flight into CSS2. They are detected in an interceptive telescope placed on a radially moving rod inside the cyclotron. Simulations were previously used to optimise different parts of the method for this range of masses: production, simultaneous injection, time-separation and identification of the ions. Experiment analysis then leads to the new mass determination, with 4 reference nuclei, of 3 N=Z nuclei: 80Zr, 76Sr, 68Se and a second mass measurement for 80Y, with a precision of 10-6. Validity of SU(4) symmetry is tested in the fp shell and the new masses importance in terms of rp process path is highlighted, in comparison with some mass models.
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A.S. Lalleman. Mesure de masses de noyaux dans la region N=Z=40. Physique Nucléaire Expérimentale [nucl-ex]. Université de Caen, 2000. Français. ⟨in2p3-00004986⟩

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