Enhanced Fusion-Evaporation Cross Sections in Neutron-Rich 132^{132}Sn on 64^{64}Ni

Evaporation residue cross sections have been measured with neutron-rich radioactive $^{132}$Sn beams on $^{64}$Ni in the vicinity of the Coulomb barrier. The average beam intensity was $2\times 10^{4}$ particles per second and the smallest cross section measured was less than 5 mb. Large subbarrier fusion enhancement was observed. Coupled-channels calculations taking into account inelastic excitation and neutron transfer underpredict the measured cross sections below the barrier.Comment: 4 pages including 1 table and 3 figure

Breakup of 17^{17}F on 208^{208}Pb near the Coulomb barrier

Angular distributions of oxygen produced in the breakup of $^{17}$F incident on a $^{208}$Pb target have been measured around the grazing angle at beam energies of 98 and 120 MeV. The data are dominated by the proton stripping mechanism and are well reproduced by dynamical calculations. The measured breakup cross section is approximately a factor of 3 less than that of fusion at 98 MeV. The influence of breakup on fusion is discussed.Comment: 7 pages, 8 figure

One-neutron transfer study of 135Te and 137Xe by particle-γ coincidence spectroscopy: The ν1i13/2 state at N = 83

Additional information is reported on single-neutron states above the doubly closed-shell nucleus 132Sn. A radioactive ion beam of 134Te(N=82) at 565 MeV and a stable ion beam of 136Xe(N=82) at 560 MeV were used to study single-neutron states in the N=8

T=1 states in Rb74 and their Kr74 analogs

Charge symmetry breaking effects that perturb analog symmetry between nuclei are usually small but are important in extracting reliable Fermi matrix elements from "superallowed" β decays and testing conserved vector current theory, especially for the heavier cases. We have used the Ca40(Ar36, pn)Rb74 and Ca40(Ca40,αpn)Rb74 reactions at 108, 123 and 160 MeV, respectively, to populate Rb74 and determine the analog distortion through comparison of T=1 states in Rb74 with their corresponding Kr74 levels. We have traced the analogs of the Kr74 ground-state band in Rb74 to a candidate spin J=8 state and determined the Coulomb energy differences. They are small and positive and increase smoothly with spin. New T=0 states were found that better delineate the deformed band structure and clarify the steps in deexcitation from high spin. A new T=0 band was found. No evidence was found for γ decay to or from a low-lying Jπ=0+ state in Rb74 despite a careful search

Terminating states in the positive-parity structures of As 67

The energy levels and γ-ray decay scheme of the positive-parity states in the Tz=12 nucleus As67 have been studied by using the Ca40(Ar36,2αp)As67 reaction at a beam energy of 145 MeV. Two new band structures have been identified which can be connected to the previously known levels. The results for these bands are compared with configuration-dependent cranked Nilsson-Strutinsky calculations. The good level of agreement between theory and experiment suggests that these structures can be interpreted in terms of configurations that involve three g92 particles and that both possess noncollective terminating states

Alignment delays in the N = Z nuclei 72Kr, 76Sr, and 80Zr

The ground state rotational bands of the N = Z nuclei 72Kr, 76Sr, and 80Zr have been extended into the angular momentum region where rotation alignment of particles is normally expected. By measuring the moments of inertia of these bands we have observed a consistent increase in the rotational frequency required to start pair breaking, when compared to neighboring nuclei. 72Kr shows the most marked effect. It has been widely suggested that these “delayed alignments” arise from np-pairing correlations. However, alignment frequencies are very sensitive to shape degrees of freedom and normal pairing, so the new experimental observations are still open to interpretation

Testing mean-field models near the N=Z line: γ-ray spectroscopy of the Tz=1/2 nucleus 73Kr

Excited states in the N=Z+1 nucleus 73Kr have been investigated using the 40Ca(36Ar, 2pn) and 40Ca(40Ca, α2pn) reactions at 145 and 160 MeV, respectively. γ rays were detected using the Gammasphere array and events were recorded in coincidence with charged-particle and neutron detectors. The three previously observed bands were extended to high spin, and a new unfavored positive-parity band has been observed. The alignment characteristics and decay properties of the bands are all consistent with large-deformation prolate rotation, with no clear evidence for oblate bands or shape coexistence. This is quite different from neighboring 72,74Kr, indicating a strong shape-stabilizing role for the valence neutron. The experimental results are compared to extended total Routhian surface, cranked Nilsson Strutinsky, and cranked relativistic mean-field calculations. The results suggest that the paired calculations lack some important physics. Neutron-proton correlations may be the missing ingredient. There is also evidence for an unusual band crossing in the negative-parity bands, which may indicate the presence of T=0 pairing correlations. At high spin all the models can reproduce the experimental data

Buang Merabak: Early evidence for human occupation in the Bismarck Archipelago, Papua New Guinea

[Extract] This paper reports new radiocarbon estimates for the age of human occupation of Buang Merabak, an archaeological site in central New Ireland, Papua New Guinea. Previously, the oldest radiocarbon date for human occupation in New Ireland was 35,410 ± 430 BP (Leavesley and Allen 1998:80). The radiocarbon determinations reported here, although preliminary, may extend the first evidence of human occupation in New Ireland to beyond 40,000 BP (uncalibrated) and indirectly support the evidence presented by Groube et al. (1986) and Chappell et al. (1994), for the occupation of the Huon Peninsula at a similar antiquity