[en] Low-spin states were studied in ³⁰Al following the β decay of ³⁰Mg produced in the fragmentation of 140-MeV/AMU ⁴⁸Ca. Analysis of the β-γ and β-γ-γ coincidences revealed a new 1⁺ state at 2413 keV, confirmation of the level scheme, and a more accurate half-life measurement of 315(6) ms for the ³⁰Mg ground state. Higher-spin states were investigated in the reaction of ¹⁴C on ¹⁸O at 22 MeV. Protons and deuterons were detected in a segmented E-ΔE Si telescope in coincidence with one or two γ rays in the FSU Ge detector array. A comparison of the resulting level and decay scheme with predictions of the sd shell model shows good agreement with all but six of the states in both excitation energy and γ-decay branching ratios. The root-mean-square deviations in energy of these states using the older USD and newer USDA and USDB interactions were 265, 176, and 173 keV, respectively. The remaining six states are well described as 4^- to 7^- states, similar in relative energy to those in ²⁸Al but shifted down by about 1200 keV. These states also agree well with the predictions of shell-model calculations using the WBP interaction. A comparison of the lowest 4^- states in even A Na, Al, and P isotopes shows a systematic decrease in energy with increasing N and with decreasing Z. The energies of the 4^- states are almost identical in nuclei with the same N-Z values

[en] The energy-level structure of ²²O with the recently identified N=14 subshell closure was investigated by the β decay of ²²N for the first time. A β-delayed-neutron, time-of-flight measurement revealed six new neutron transitions attributed to the β decay of ²²N. One- and two-β-delayed neutron decay of ²²N, with emission probabilities of 33(3)% and 12(3)%, respectively, were observed to correspond to four new negative-parity states in ²²O. The half-life of ²²N β decay was determined to be 20(2) ms. Three γ-ray transitions in ²²O and single γ rays in ²¹O and ²⁰O were observed following the β decay of ²²N. The observation of large Gamow-Teller strength for a highly excited state in ²²O indicates a halo structure for ²²N. A comparison of results with shell-model predictions showed overall poor agreement. The measured P_n values of ²⁴O and ²⁵F components of the secondary beam showed an enhancement relative to the P_n values of adjacent oxygen and fluorine isotopes, providing additional evidence for the N=14 closed subshell.

[en] The nuclear states in ²³F have been investigated following the β decay of ²³O. The measurement of ²³O was carried out at the National Superconducting Cyclotron Laboratory using fragments from the reaction of a ⁴⁸Ca beam in a Be target. The half-life and total neutron emission probability were determined to be 97(8) ms and 7(2)%, respectively, for ²³O β decay. Ten γ-ray decays in ²³F and a single γ-ray in ²²F were observed to establish the β decay scheme for ²³O. Shell model calculations are in reasonable agreement with the measured β branching and B(GT) values for the lowest energy state. The excitation energies of the first 1/2⁺ and 3/2⁺ states have been determined to be 2243(8) and 4066(16) keV, respectively, indicating a widening of the 5/2⁺-1/2⁺ state gap in ²³F. The decay scheme of the largest contaminant ²⁶Ne in the experiment was established

[en] Two-neutron knockout reactions from nuclei in the proximity of the proton dripline have been studied using intermediate-energy beams of neutron-deficient ³⁴Ar, ³⁰S, and ²⁶Si. The inclusive cross sections, and also the partial cross sections for the population of individual bound final states of the ³²Ar, ²⁸S and ²⁴Si knockout residues, have been determined using the combination of particle and γ-ray spectroscopy. Similar to the two-proton knockout mechanism on the neutron-rich side of the nuclear chart, these two-neutron removal reactions from already neutron-deficient nuclei are also shown to be consistent with a direct reaction mechanism

[en] The neutron-rich nucleus ³⁰Na in the vicinity of the 'Island of Inversion' was investigated using intermediate-energy Coulomb excitation. A single γ-ray transition was observed and attributed to the 3₁⁺→2_gs⁺ decay. A transition probability of B(E2;2_gs⁺→3₁⁺)=147(21) e² fm⁴ was determined and found in agreement with a previous experiment and with large-scale shell-model calculations. Evidence for the strong excitation of the 4₁⁺ state predicted by the shell-model calculations was not observed

[en] The shell structure underlying shape changes in neutron-rich nuclei between N=20 and N=28 has been investigated by a novel application of the transient field technique to measure the first-excited state g factors in ³⁸S and ⁴⁰S produced as fast radioactive beams. Details of the new methodology are presented. In both ³⁸S and ⁴⁰S there is a fine balance between the proton and neutron contributions to the magnetic moments. Shell-model calculations that describe the level schemes and quadrupole properties of these nuclei also give a satisfactory explanation of the g factors. In ³⁸S the g factor is extremely sensitive to the occupation of the neutron p_3/2 orbit above the N=28 shell gap as occupation of this orbit strongly affects the proton configuration. The g factor of deformed ⁴⁰S does not resemble that of a conventional collective nucleus because spin contributions are more important than usual

[en] The breakdown of the N=20 magic number in the so-called island of inversion around ³²Mg 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 ³⁰Mg and ³²Mg, with the latter consisting nearly purely of 2p-2h N=20 cross-shell configurations. Single-neutron knockout experiments on ^30,32Mg 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