Un piégeage d’ions optimal pour la mesure de masse de noyaux exotiques dans la région (magique ?) de N=40

Magic numbers or shell closures, are an important feature of nuclear structure, but now found to be modified far from stability. Determination of the nuclear binding energy via mass measurements of exotic nuclides represents one of the greatest challenges in the study of nuclear structure due to the high precision required and the low production rates and short half-lives. To solve the problem, the complementary spectrometers MISTRALand ISOLTRAP may be used, both located at ISOLDE/CERN (Geneva). MISTRAL is a transmission mass spectrometer for very short-lived nuclides, and ISOLTRAP a Penningtrap mass spectrometer providing exceptional precision. This thesis describes improvements in the limitations of these complementary instruments: a beam cooler to increase the sensitivity of MISTRAL and an optimization procedure to improve the definition ofthe ISOLTRAP trapping fields. High-precision mass measurements were performed at ISOLTRAP to extend the backbone of well-known nuclides in the mass table, and to finely examine the case for new magic numbers N = 32 and 40. The results illustrate a subtle effect of extra binding energy for $^{56}$Cr$_{32}$ in the presence of a probable deformation. Practically no additional binding is found for $^{68}$Ni$_{40}$ though a small effect is visible, perhaps in conjunction with a competitive mid-shell effect at N = 39.