Radioactive ion beams of 17F were used to study several resonance states in 18Ne. Clear evidence for simultaneous two-proton emission from the 6.15 MeV state (Jpi = 1(-)) in 18Ne has been observed with the reaction 17F+1H. Because of limited angular coverage, the data did not differentiate between the two possible mechanisms of simultaneous decay, diproton (2He) emission or direct three-body decay. The two-proton partial width was found to be 21+/-3 eV assuming 2He emission and 57+/-6 eV assuming three-body decay. The total width of the 1(-) state was measured to be 50+/-5 keV. Several additional resonances that decay by single proton emission were also studied.

Evaporation residue and fission cross sections of radioactive 132 Sn on 64 Ni were measured near the Coulomb barrier. A large subbarrier fusion enhancement was observed. Coupled-channel calculations, including inelastic excitation of the projectile and target, and neutron transfer are in good agreement with the measured fusion excitation function. When the change in nuclear size and shift in barrier height are accounted for, there is no extra fusion enhancement in 132 Sn + 64 Ni with respect to stable Sn + 64 Ni. A systematic comparison of evaporation residue cross sections for the fusion of even 112−124 Sn and 132 Sn with 64 Ni is presented. DOI: 10.1103/PhysRevC.75.054607 PACS number(s): 25.60.−t, 25.60.Pj 0556-2813/2007/75(5)/054607(9) 054607-1

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The elastic scattering of heavy ions at large angles has received much attention since the measurements of Braun-Munzinger et at. 1 first revealed an enhanced cross section for scattering of 16 0+ 28 Si at center-of-mass angles larger than 100°. 2 The backward-angle enhancement seems to be a general feature for projectiles and targets in this mass region, although the size of the enhancement can vary markedly from system to system. A number of explanations have been offered for this phenomenon, such as Regge poles, 3 resonances, 4 parity-dependent potentials, 5 diffraction, 6 and particle exchange. 7 The regular broad structures appearing in the excitation functions could also be explained by orbiting in the mutual potential. 8 It would be desirable to have additional experimental data which might help in distinguishing among these various pictures. Since the interpretation of backward-angle enhancement in terms of the orbiting of projectile 6 M 0 Berlanger et al. 9 and target should have general consequences for inelastic scattering as well, 9 we have investigated the gross features of the inelastic scattering at backward angles. Experimental data of this type are reported here for the first time. We find both for the system 12 C + 20 Ne, on which we report here, and for other systems as well, 10 a strong enhancement of the cross section for inelastic scattering with large negative Q values at backward angles. The gross features we observe for the inelastic scattering find a natural interpretation in terms of orbiting and support this mechanism as the origin of backward-angle enhancement of elastic scattering as well.A natural carbon target was bombarded with beams of 50-to 80-MeV 20 Ne 4+ from the Oak Ridge isochronous cyclotron. The reaction products with Z> 3 were identified with a positionsensitive AE-E counter 11 which spanned an angular range of 9° in 1° steps. Angular distributions An experimental study of the 20 Ne + 12 C systems reveals a large cross section for inelastic scattering with large negative Q values at backward angles. The differential cross section is proportional to l/sin0 Coirio >100° and has characteristics consistent with the decay of an orbiting 20 Ne + 12 C dinuclear system.

The rates of the 18 F͑p , ␣͒ 15 O and 18 F͑p , ␥͒ 19 Ne reactions in astrophysical environments depend on the properties of 19 Ne levels above the 18 F+ p threshold. There are at least eight levels in the mirror nucleus 19 F for which analogs have not been observed in 19 Ne in the excitation energy range E x = 6.4-7.6 MeV. These levels may significantly enhance the 18 F+ p reaction rates, and thus we have made a search for these levels by measuring the 1 H͑ 18 F, p͒ 18 F excitation function over the energy range E c.m. = 0.3-1.3 MeV. We have identified and measured the properties of a newly observed level at E x = 7.420± 0.014 MeV, which is most likely the mirror to the J = 7 2 + 19 F level at 7.56 MeV. We have additionally found a significant discrepancy with a recent compilation for the properties of a 19 Ne state at E x = 7.5 MeV and set upper limits on the proton widths of missing levels.

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We have discovered an error in our data analysis that affects the result presented in our recent Letter. The evaporation residue cross sections were calculated using the residue yield and the integrated beam. Because elements of the data array used to store the integrated beam did not have sufficient range (maximum 2 16 ), an overflow caused the integrated beam to be counted incorrectly. This was discovered by repeating some of the measurements and checked by reanalyzing the previous data with an appropriately sized data array, and using the originally sized data array but breaking up the analysis into smaller subsets. The correct cross section is presented here in Fig. 1 which replaces Fig. 2 of the original Letter. The size of the correction increases as the beam energy decreases because measurements at lower energies take longer times. At the lowest energy, the corrected cross section is a factor of 4 less than the previously published value. Since a thick target was used, the effective reaction energy was deduced by taking a cross-section-weighted average over the range of the energy loss in the target. The corrected excitation function has a steeper slope at lower energies; therefore, the calculated effective reaction energy is shifted to higher values. Fusion is still enhanced in 132 Sn on 64 Ni at sub-barrier energies with respect to a one-dimensional barrier penetration model prediction. The enhancement of fusion relative to lighter Sn isotopes is no larger than would be expected due to the larger nuclear radius of 132 Sn and transfer does not appear to play a major role in the sub-barrier fusion for this system.[1] W. S. Freeman et al., Phys. Rev. Lett. 50, 1563 (1983.[2] R. Bass, Nucl. Phys. A231, 45 (1974). FIG. 1 (color online). Fusion-evaporation excitation functions of 132 Sn 64 Ni and 64 Ni on even 112-124 Sn [1]. The reaction energy is scaled by the fusion barrier predicted by the Bass model [2] and the evaporation residue (ER) cross section is scaled by the size of the reactants using R 1:2A 1=3 p A 1=3 t , where A p (A t ) is the mass of the projectile (target). The filled circles are corrected data and the open circle is our measurement using a 124 Sn beam.