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Abstract. The energy of the lowest deformed 2-particle 2-hole (2p2h) 0 + state in even-even N = 20 nuclei is a key observable directly related to the size of the neutron N = 20 shell closure. 34 Si, with 14 protons and 20 neutrons, lies at the boundary of the "island of inversion", where the deformed 2p2h 0 + state is the ground state in even-A nuclei. In 34 Si, the 2p2h 0 + state is expected to be particularly low lying -in some theories it is even predicted to lie below the first 2 + state. While there have been a number of attempts, using various techniques, no experiment to date has been able to firmly locate the 34 Si 2p2h 0 + state although a number of candidates have been suggested. Here we present, for the first time, data obtained from a fusion-evaporation reaction 18 O( 18 O, 2p) to produce 34 Si. Gammasphere and Microball were used to detect γ-γ coincidences and charged particles (two protons), respectively. The increased sensitivity of this experiment using γ-γ coincidences and a high charged-particle detection efficiency helped to exclude previously reported candidates and provided a stringent limit on the anticipated γ decay from the first 2 + state to the 2p2h 0 + state.

The authors present an investigation of the modification caused by an intense laser field to the rates of mJ changing collisions for Hg perturbed by argon. They have studied experimentally the competition between radiative and collisional coupling between mJ states with a strong laser field tuned to the Hg J=1 to J=1 transition at lambda 435.8 nm. Population is pumped into the strongly dressed manifold from the ground state with a weak UV 'probe' laser detuned slightly from the lambda 253.7 nm intercombination line. The fluorescence observed at lambda 404.7 nm depends critically on whether the excitation proceeds via collisional redistribution or resonance through Stark shifted levels. The authors present data that clearly exhibit the effects of this competition. The data show in particular how one can produce excitation to transient Stark shifted levels in the presence of collisions. This will be critical in future experiments on collisions in strong fields.