High-precision masses of 29-33 Mg and the N = 20 shell “closure”

. High-precision mass measurements have been performed on the exotic magnesium isotopes 29-33 Mg using the MISTRAL radiofrequency spectrometer, especially suited for very short-lived nuclides. This method, combined with the powerful tool of resonant laser ionization at ISOLDE, has provided a significant reduction of uncertainty for the masses of the most exotic Mg isotopes: a relative error of 7×10 -7 was achieved for the weakly produced 33 Mg that has a half-life of only 90ms. Moreover, the mass of 33 Mg is found to change by over 250keV. Verifying and minimizing binding energy uncertainties in this region of the nuclear chart is important for understanding the lack of binding energy that is normally associated with magic numbers.