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The heaviest bound isotope of boron 19 B has been investigated using exclusive measurements of its Coulomb dissociation, into 17 B and two neutrons, in collisions with Pb at 220 MeV=nucleon. Enhanced electric dipole (E1) strength is observed just above the two-neutron decay threshold with an integrated E1 strength of BðE1Þ ¼ 1.64 AE 0.06ðstatÞ AE 0.12ðsysÞ e 2 fm 2 for relative energies below 6 MeV. This feature, known as a soft E1 excitation, provides the first firm evidence that 19 B has a prominent two-neutron halo. Three-body calculations that reproduce the energy spectrum indicate that the valence neutrons have a significant s-wave configuration and exhibit a dineutronlike correlation.

Detailed spectroscopy of the neutron-unbound nucleus 28 F has been performed for the first time following proton/neutron removal from 29 Ne/ 29 F beams at energies around 230 MeV/nucleon. The invariant-mass spectra were reconstructed for both the 27 F ( * ) + n and 26 F ( * ) + 2n coincidences and revealed a series of well-defined resonances. A near-threshold state was observed in both reactions and is identified as the 28 F ground state, with Sn( 28 F) = −199(6) keV, while analysis of the 2n decay channel allowed a considerably improved Sn( 27 F) = 1620(60) keV to be deduced. Comparison with shell-model predictions and eikonal-model reaction calculations have allowed spin-parity assignments to be proposed for some of the lower-lying levels of 28 F. Importantly, in the case of the ground state, the reconstructed 27 F+n momentum distribution following neutron removal from 29 F indicates that PACS numbers:

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