The energies of the excited states in very neutron-rich (42)Si and (41,43)P have been measured using in-beam gamma-ray spectroscopy from the fragmentation of secondary beams of (42,44)S at 39A MeV. The low 2(+) energy of (42)Si, 770(19) keV, together with the level schemes of (41,43)P, provides evidence for the disappearance of the Z=14 and N=28 spherical shell closures, which is ascribed mainly to the action of proton-neutron tensor forces. New shell model calculations indicate that (42)Si is best described as a well-deformed oblate rotor.

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The 0 þ 2 state in 34 Si has been populated at the GANIL-LISE3 facility through the decay of a newly discovered 1 þ isomer in 34 Al of 26(1) ms half-life. The simultaneous detection of e þ e À pairs allowed the determination of the excitation energy Eð0 þ 2 Þ ¼ 2719ð3Þ keV and the half-life T 1=2 ¼ 19:4ð7Þ ns, from which an electric monopole strength of 2 ðE0Þ ¼ 13:0ð0:9Þ Â 10 À3 was deduced. The 2 þ 1 state is observed to decay both to the 0 þ 1 ground state and to the newly observed 0 þ 2 state [via a 607(2) keV transition] with a ratio Rð2Gathering all information, a weak mixing with the 0 þ 1 and a large deformation parameter of ¼ 0:29ð4Þ are found for the 0 þ 2 state, in good agreement with shell model calculations using a new SDPF-U-MIX interaction allowing np-nh excitations across the N ¼ 20 shell gap.

The structure of 44S has been studied by using delayed γ and electron spectroscopy. The decay rates of the 02+ isomeric state to the 2(1)+ and 0(1)+ states, measured for the first time, lead to a reduced transition probability B(E2: 2(1)+→0(2)+)=8.4(26) e(2) fm4 and a monopole strength ρ2(E0: 0(2)+→0(1)+)=8.7(7)×10(-3). Comparisons to shell model calculations point towards prolate-spherical shape coexistence, and a two-level mixing model is used to extract a weak mixing between the two configurations.

In-beam ␥-ray spectroscopy using fragmentation reactions of both stable and radioactive beams has been performed in order to study the structure of excited states in neutron-rich oxygen isotopes with masses ranging from A = 20 to 24. For the produced fragments, ␥-ray energies, intensities, and ␥-␥ coincidences have been measured. Based on this information new level schemes are proposed for