Strong Evidence for

The boundaries of the chart of nuclides contain exotic isotopes that possess extreme proton-to-neutron asymmetries. Here we report on strong evidence of ^{9}N, one of the most exotic proton-rich isotopes where more than one half of its constitute nucleons are unbound. With seven protons and two neutrons, this extremely proton-rich system would represent the first-known example of a ground-state five-proton emitter. The invariant-mass spectrum of its decay products can be fit with two peaks whose energies are consistent with the theoretical predictions of an open-quantum-system approach; however, we cannot rule out the possibility that only a single resonancelike peak is present in the spectrum.

Observation of the Exotic Isotope

A ^{13}F resonance was observed following a charge-exchange reaction between a fast ^{13}O beam and a ^{9}Be target. The resonance was found in the invariant-mass distribution of 3p+^{10}C events and probably corresponds to a 5/2^{+} excited state. The ground state was also expected to be populated, but was not resolved from the background. The observed level decays via initial proton emissions to both the ground and first 2^{+} state of ^{12}O, which subsequently undergo 2p decay. In addition, there may also be a significant proton decay branch to the second 2^{+} level in ^{12}O. The wave function associated with the observed level may be collectivized due to coupling to the continuum as is it located just above the threshold for proton decay to the 2_{2}^{+} state of ^{12}O.

Systematic Matter and Binding-Energy Distributions from a Dispersive Optical Model Analysis.

We present the first systematic nonlocal dispersive optical model analysis using both bound-state and scattering data of ^{16,18}O, ^{40,48}Ca, ^{58,64}Ni, ^{112,124}Sn, and ^{208}Pb. In all systems, roughly half the total nuclear binding energy is associated with the most-bound 10% of the total nucleon density. The extracted neutron skins reveal the interplay of asymmetry, Coulomb, and shell effects on the skin thickness. Our results indicate that simultaneous optical model fits of inelastic scattering and structural data on isotopic pairs are effective for constraining asymmetry-dependent nuclear structural quantities otherwise difficult to observe experimentally.

First Observation of Unbound

The structure of the extremely proton-rich nucleus _{8}^{11}O_{3}, the mirror of the two-neutron halo nucleus _{3}^{11}Li_{8}, has been studied experimentally for the first time. Following two-neutron knockout reactions with a ^{13}O beam, the ^{11}O decay products were detected after two-proton emission and used to construct an invariant-mass spectrum. A broad peak of width ∼3.4 MeV was observed. Within the Gamow coupled-channel approach, it was concluded that this peak is a multiplet with contributions from the four lowest ^{11}O resonant states: J^{π}=3/2_{1}^{-}, 3/2_{2}^{-}, 5/2_{1}^{+}, and 5/2_{2}^{+}. The widths and configurations of these states show strong, nonmonotonic dependencies on the depth of the p-^{9}C potential. This unusual behavior is due to the presence of a broad threshold resonant state in ^{10}N, which is an analog of the virtual state in ^{10}Li in the presence of the Coulomb potential. After optimizing the model to the data, only a moderate isospin asymmetry between ground states of ^{11}O and ^{11}Li was found.

Large Longitudinal Spin Alignment of Excited Projectiles in Intermediate Energy Inelastic Scattering.

We study the sequential breakup of E/A=24.0 MeV ^{7}Li projectiles excited through inelastic interactions with C, Be, and Al target nuclei. For peripheral events that do not excite the target, we find very large spin alignment of the excited ^{7}Li projectiles longitudinal to the beam axis. This spin alignment is independent of the target used, and we propose a simple alignment mechanism that arises from an angular-momentum-excitation-energy mismatch. This mechanism is independent of the potential used for scattering and should be present in many scattering experiments.