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The relationship between the Coulomb displacement energy for the A=8, J=2 + , T=1 state and the low-energy astrophysical S 17 factor for the 7 Be(p,γ) 8 B reaction is discussed. The displacement energy is interpreted in a particle-hole model. The dependence of the particle displacement energy on the potential well geometry is investigated and is used to relate the particle displacement energy to the rms radius and the asymptotic normalization of the valence proton wave function in 8 B. The asymptotic normalization is used to calculate the astrophysical S 17 factor for the 7 Be(p,γ) reaction. The relationship to the 7 Li(n,γ) reaction, the 8 B quadrupole moment, radial density, and break-up momentum distribution are also discussed.

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A measurement of the direct two-proton removal from 42 Si has provided the first structural information on the N = 28 isotone 40 Mg. The value for the inclusive cross section for two-proton removal from 42 Si of 40 +27 −17 μb is significantly lower than that predicted by structure calculations using the recent SDPF-MU shell-model effective interaction combined with eikonal reaction theory. This observed discrepancy is consistent with the interpretation that only one of the predicted low-lying 0 + states in 40 Mg is bound. A two-state mixing analysis describing two-proton knockout cross sections along N = 28 provides support for the interpretation of a prolate-deformed 40 The study of nuclei far from the line of β stability is one of the most active and challenging areas of current nuclear structure physics. Exotic combinations of protons (Z) and neutrons (N ) can significantly affect the underlying shell structure, and for weakly bound nuclei at or near the dripline, the proximity to continuum states may further alter nuclear properties. Benchmarking and constraining theory at the very limits of existence is critical, and one of the most exotic neutron-rich nuclei currently accessible to experiment is 40 Mg.First observed following fragmentation of a 48 Ca primary beam at the National Superconducting Cyclotron Laboratory in 2007 (with three events) [1], 40 12 Mg 28 lies at an intersection for nucleon magic numbers and the neutron dripline. It is expected to exhibit [2] the collective and deformed properties characteristic of the N = 28 isotones below 48 Ca, which is a region of rapidly changing nuclear shapes. Large-scale shell-model calculations predict that 40 Mg should be a welldeformed prolate rotor [3]. In addition, the last bound neutron orbital is expected to be the low-l p 3/2 state, leading to the possibility that weak binding effects could play a role.Further, deformation along the Z = 12 isotopic chain has been of recent experimental interest, with the work of Doornenbal et al. [4], in which an extended region of deformation in the Mg isotopes from the quenched N = 20 gap out to N = 26 is observed, as determined by the ratio of E(4 + 1 )/E(2 + 1 ), and is expected to persist at N = 28. We present here the first experimental structure information on 40 Mg following measurement of the inclusive two-proton removal cross section from 42 Si and discuss the results as a part of the overall shape evolution along the N = 28 isotonic chain. We provide a limit on the number of bound states predicted by theory, and evidence supporting a prolate-deformed 40 Mg ground state based on a two-state mixing model.One-and two-proton knockout reactions from 42 Si were carried out at Radioactive Isotope Beam Factory (RIBF), operated by RIKEN Nishina Center and the Center for Nuclear Study, University of Tokyo. A primary beam of 48 Ca, at an energy of 345 MeV/nucleon, with an average intensity of approximately 70 pnA, was fragmented in a thick (15-mm) rotating Be production target to produce a cocktail of projectile...

The region of nuclei close to the neutron dripline is important in nuclear synthesis, and is one where weak nucleon binding and changes in the neutron-proton ratio (N/Z) can dramatically affect the underlying shell structure and nuclear properties. While technical advances continue to extend the frontier of neutron-rich nuclei, many remain beyond experimental reach and it is necessary to rely on calculation. In this context, the near-dripline fluorine and neon nuclei, with proton numbers Z = 9, 10 and neutron number N ∼ 20, provide a unique region accessible to experiment, where the effects of weak binding and increasing N/Z asymmetry coexist and can give rise to measurable effects. It is here, for example, that N = 20 ceases to be a "magic" shell closure [1] and a new shell gap emerges at N = 16. This is also where a dramatic jump in stability occurs between oxygen and fluorine, i.e., adding one proton extends the location of the dripline an extra six neutrons from 24 8 O 16 to 31 9 F 22 . The breakdown of the N = 20 shell gap is an example of nucleon-nucleon (spin-isospin, T = 0) interactions modifying single-particle energies and driving shell evolution [2] as well as deformation [3,4]. This gives rise to the well known "island of inversion" [5][6][7][8] around 32 Mg; where nuclear shapes switch from spherical to deformed due to the enhanced contribution from correlations generated by promoting neutron pairs across the reduced sd-fp (N = 20) shell gap. The enhanced stability of the most neutron-rich fluorine isotopes has also been linked [9] to a broken N = 20 shell and the increased contribution from correlations due to large fp-shell ("intruder") occupancy.In this Rapid Communication we present data and calculations on 30 10 Ne 20 , which is situated close to the last known, possibly last bound, isotopes of neon ( 34 Ne) and fluorine ( 31 F) and is also within the island of inversion. The cross section for the 32 Mg two-proton knockout reaction is measured and is found to be suppressed compared to calculation, indicating larger than predicted structural changes between the initial 32 Mg ground state and 30 Ne final states. The cross-section data are used to estimate the neutron fp-shell occupation probabilities in 30 Ne. We discuss these results in the context of the N = 20 shell gap and enhanced stability of neutron-rich 29,31 F.Data were taken in two experiments at the National Superconducting Cyclotron Laboratory at Michigan State University. In both experiments 32 Mg ions were produced by fragmenting a 140 MeV/nucleon 48 Ca beam on a 850 mg/cm 2 9 Be production target. The A1900 fragment separator [10], operated with a 2% momentum acceptance, was used to select and transport the 32 Mg ions to the S800 [11] beamline where they underwent reactions on a second 9 Be target at the target position of the S800 spectrograph. In the first (second) experiment the 32 Mg secondary beam energy was 99.7 (86.7) MeV/nucleon incident on a 565 (376) mg/cm 2 9 Be target.30 Ne fragments were identified by momentum and ener...