Abstract : Proton and two proton emission from light neutron deficient nuclei around A=20 have been studied. A radioactive beam of 18Ne, 17F and 20Mg, produced at the Grand Accélérateur National d'Ions Lourds by fragmentation of a 24Mg primary beam at 95MeV/A, bombarded a 9Be target to form unbound states. Proton(s) and nuclei from the decay were detected respectively in the MUST array and the SPEG spectrometer. From energy and angle measurements, the invariant mass of the decaying nucleus could be reconstructed.
Double coincidence events between a proton and 17F, 16O, 15O, 14O and 18Ne were registered to obtain excitation energy spectra of 18Ne, 17F, 16F, 15F et 19Na. Generally, the masses measures are in agreement with previous experiments. In the case of 18Ne, excitation energy and angular distributions agree well with the predictions of a break up model calculation. From 17Ne proton coincidences, a first experimental measurement of the ground state mass excess of 18Na has been obtained and yields 24,19(0,15)MeV.
Two proton emission from 17Ne and 18Ne excited states and the 19Mg ground state was studied through triple coincidences between two proton and 15O, 16O and 17Ne respectively. In the first case, the proton-proton relative angle distribution in the center of mass has been compared with model calculation. Sequential emission from excited states of 17Ne, above the proton emission threshold, through 16F is dominant but a 2He decay channel could not be excluded. No 2He emission from the 1,288MeV 17Ne state, or from the 6,15MeV 18Ne state has been observed. Only one coincidence event between 17Ne and two proton was registered, the value of the one neutron stripping reaction cross section of 20Mg being much lower than predicted.