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Stucture of N = 17,18 nuclei has been investigated via proton inelastic scattering and neutron removal reactions up to the neutron dripline in inverse kinematics by use of radioctive ion beams provided by the RIKEN isotope separator, RIPS. Low energy excited states have been found in all the 26,27F and 27Ne nuclei, which are out of the neutron sd shell configuration space and are considered as intruder states arisng from cross shell excitations. Monte-Carlo shell model calculations with the sdpf-m interaction predict low energy negative parity excited states from neutron cross shell excitation at N = 17,18, which is in agreement with our experimental results. Observation of intruder states even at N = 17, especially the p3/2 state in 27Ne at 765 keV is a clear indication of a vanishing N = 20 shell gap at Z = 8 as predicted by the sdpf-m shell model calculations.

A novel method has been established to realize the experiment of electron scattering off short-lived nuclei. The method was based on the well known "ion trapping" phenomenon in electron storage rings. In the R&D experiments at Kyoto University, stable nucleus, 133Cs, was employed as the target nucleus. The luminosity of scattering experiment was nearly 1026 cm−2s−1 at electron beam current around 75 mA. The angular distribution of elastically scattered electrons from trapped Cs ions was measured and the result was well fitted by theoretical calculation. It was indicated that higher luminosity can be reached with larger electron beam current.

We have studied the 2 1 + state in neutron-rich {sr16}C via inelastic proton scattering in inverse kinematics, using a 33 MeV/nucleon beam. From the angle-integrated cross-section, the deformation parameter β pp′ = 0.50(8) is obtained. This value is greater than the deformation parameter deduced from the lifetime measurement. With these two result combined, the ratio of the neutron and proton quadrupole matrix elements is deduced to be approximately 7, indicating a neutron-dominant quadrupole collectivity in 16C

The behavior of the nuclear shell structure far away from the valley of stability is discussed in this paper with an emphasis on the N = 20 magic number. Two experimental examples, namely γ-spectroscopy of 27Ne by 1H(28Ne, 27Ne) reaction and single-particle spectroscopy of 23O by 22O(d, p)23O* → 22O+n process in inverse kinematics, are shown providing indirect indication and a direct evidence for the extreme decrease of the N = 20 shell gap and, consequently, the vanishing N = 20 magicity.