Both one-proton and one-neutron knockout reactions were performed with fast beams of two asymmetric, neutron-deficient rare isotopes produced by projectile fragmentation. The reactions are used to probe the nucleon spectroscopic strengths at both the weakly and strongly bound nucleon Fermi surfaces. The one-proton knockout reactions 9 Be( 28 S, 27 P)X and 9 Be( 24 Si, 23 Al)X probe the weakly bound valence proton states and the one-neutron knockout reactions and 9 Be( 28 S, 27 S)X and 9 Be( 24 Si, 23 Si)X the strongly bound neutron states in the two systems. The spectroscopic strengths are extracted from the measured cross sections by comparisons with an eikonal reaction theory. The reduction of the experimentally deduced spectroscopic strengths, relative to the predictions of shell-model calculations, is of order 0.8-0.9 in the removal of weakly bound protons and 0.3-0.4 in the knockout of the strongly bound neutrons. These results support previous studies at the extremes of nuclear binding and provide further evidence that in asymmetric nuclear systems the nucleons of the deficient species, at the more-bound Fermi surface are more strongly correlated than those of the more weakly bound excess species.

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The breakdown of the N = 20 magic number in the so-called island of inversion around 32 Mg is well established. Recently developed large-scale shell-model calculations suggest a transitional region between normal-and intruder-dominated nuclear ground states, thus modifying the boundary of the island of inversion. In particular, a dramatic change in single-particle structure is predicted between the ground states of 30 Mg and 32 Mg, with the latter consisting nearly purely of 2p-2h N = 20 cross-shell configurations. Single-neutron knockout experiments on 30,32 Mg projectiles have been performed. We report on a first direct observation of intruder configurations in the ground states of these very neutron-rich nuclei. Spectroscopic factors to low-lying negative-parity states in the knockout residues are deduced and compare well with shell-model predictions.

The neutron-rich nucleus 144 Ba (t 1/2 =11.5 s) is expected to exhibit some of the strongest octupole correlations among nuclei with mass numbers A less than 200. Until now, indirect evidence for such strong correlations has been inferred from observations such as enhanced E1 transitions and interleaving positive-and negative-parity levels in the ground-state band. In this experiment, the octupole strength was measured directly by sub-barrier, multi-step Coulomb excitation of a postaccelerated 650-MeV 144 Ba beam on a 1.0-mg/cm 2 208 Pb target. The measured value of the matrix element, 3 − 1 M(E3) 0 + 1 = 0.65( +17 −23 ) eb 3/2 , corresponds to a reduced B(E3) transition probability of 48( +25 −34 ) W.u. This result represents an unambiguous determination of the octupole collectivity, is larger than any available theoretical prediction, and is consistent with octupole deformation.

We report on the first in-beam γ-ray spectroscopy of 23 Al using two different reactions at intermediate beam energies: inelastic scattering off 9 Be and heavy-ion induced one-proton pickup, 9 Be( 22 Mg, 23 Al+γ)X, at 75.1 MeV/nucleon. A γ-ray transition at 1616(8) keV -exceeding the proton separation energy by 1494 keVwas observed in both reactions. From shell model and proton decay calculations we argue that this γ-ray decay proceeds from the core-excited 7/2 + state to the 5/2 + ground state of 23 Al. The proposed nature of this state, [ 22 Mg(2 + 1 ) ⊗ πd 5/2 ] 7/2 + , is consistent with the presence of a γ-branch and with the population of this state in the two reactions.Since its discovery in 1969 [1], the neutron-deficient nucleus 23 Al has attracted much attention. 23 Al is four neutrons removed from stable 27 Al and is the last proton-bound, odd-mass aluminum isotope known to exist. The low proton separation energy of S p = 122(19) keV [2] made 23 Al a candidate for a proton halo system. From the measurement of an enhanced reaction cross section, 23 Al was indeed proposed to have a proton-halo structure with a J π = 1/2 +

The neutron-rich N = 50 isotones 82