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The astrophysical S factor for the radiative proton capture reaction on Be7 (S17) at low energies is affected by the s-wave scattering lengths. We report the measurement of elastic and inelastic scattering cross sections for the Be7+p system in the center-of-mass energy range 0.474-2.740 MeV and center-of-mass angular range 70-150. A radioactive Be7 beam produced at Oak Ridge National Laboratory's (ORNL) Holifield Radioactive Ion Beam Facility was accelerated and bombarded a thin polypropylene (CH2)n target. Scattered ions were detected in the segmented Silicon Detector Array. Using an R-matrix analysis of ORNL and Louvain-la-Neuve cross-section data, the s-wave scattering lengths for channel spins 1 and 2 were determined to be 17.34-1.33+1.11 and -3.18-0.50+0.55 fm, respectively. The uncertainty in the s-wave scattering lengths reported in this work is smaller by a factor of 5-8 compared to the previous measurement, which may reduce the overall uncertainty in S17 at zero energy. The level structure of B8 is discussed based upon the results from this work. Evidence for the existence of 0+ and 2+ levels in B8 at 1.9 and 2.21 MeV, respectively, is observed.

In atomic nuclei, the spin-orbit interaction originates from the coupling of the orbital motion of a nucleon with its intrinsic spin. Recent experimental and theoretical works have suggested a weakening of the spin-orbit interaction in neutron-rich nuclei far from stability. To study this phenomenon, we have investigated the spin-orbit energy splittings of single-hole and single-particle valence neutron orbits of $^{132}$Sn. The spectroscopic strength of single-hole states in $^{131}$Sn was determined from the measured differential cross sections of the tritons from the neutron-removing $^{132}$Sn(d, t)$^{131}$Sn reaction, which was studied in inverse kinematics at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. The spectroscopic factors of the lowest 3/2+, 1/2+ and 5/2+ states were found to be consistent with their maximal values of (2j+1), confirming the robust N=82 shell closure at $^{132}$Sn. We compared the spin-orbit splitting of neutron single-hole states in $^{131}$Sn to those of single-particle states in $^{133}$Sn determined in a recent measurement of the $^{132}$Sn(d, p)$^{133}$Sn reaction. We found a significant reduction of the energy splitting of the weakly bound 3p orbits compared to the well-bound 2d orbits, and that all the observed energy splittings can be reproduced remarkably well by calculations using a one-body spin-orbit interaction and a Woods–Saxon potential of standard radius and diffuseness. The observed reduction of spin-orbit splitting can be explained by the extended radial wavefunctions of the weakly bound orbits, without invoking a weakening of the spin-orbit strength.

GODDESS is a coupling of the charged-particle detection system ORRUBA to the gamma-ray detector array Gammasphere. This coupling has been developed in order to facilitate the high-resolution measurement of direct reactions in normal and inverse kinematics with stable and radioactive beams. GODDESS has been commissioned using a beam of 134Xe at 10 MeV/A, in a campaign of stable beam measurements. The measurement demonstrates the capabilities of GODDESS under radioactive beam conditions, and provides the first data on the single-neutron states in 135Xe, including previously unobserved states based on the orbitals above the N=82 shell closure.

WOS: 000237157300019, The F-19 nucleus has been studied extensively. However, there have been no comprehensive experimental studies of F-18+n single-particle components in F-19, and no measure of neutron vacancies in the F-18 ground state, as such experiments require a (radioactive) F-18 target or beam. We have used the H-2(F-18,p)F-19 reaction to selectively populate states in F-19 that are of F-18+n character. The 108.5-MeV radioactive F-18(+9) beam was provided by the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. Proton-recoil coincidence data were taken for both alpha-decaying and particle-stable final states. Angular distributions and spectroscopic factors were measured for nine proton groups, corresponding to 13 states in F-19. The results are compared to shell model calculations.

The F19 nucleus has been studied extensively. However, there have been no comprehensive experimental studies of F18+n single-particle components in F19, and no measure of neutron vacancies in the F18 ground state, as such experiments require a (radioactive) F18 target or beam. We have used the H2(F18,p)F19 reaction to selectively populate states in F19 that are of F18+n character. The 108.5-MeV radioactive F18+9 beam was provided by the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. Proton-recoil coincidence data were taken for both α-decaying and particle-stable final states. Angular distributions and spectroscopic factors were measured for nine proton groups, corresponding to 13 states in F19. The results are compared to shell model calculations.

The rates of the 18F(p, ?)15O and 18F(p, ?)19Ne reactions in astrophysical environments depend on the properties of 19Ne levels above the 18F + p threshold. There are at least 8 levels in the mirror nucleus 19F for which analogs have not been observed in 19Ne in the excitation energy range Ex = 6.4 - 7.6 MeV. These levels may significantly enhance the 18F + p reaction rates, and thus we have made a search for these levels by measuring the 1H(18F,p)18F excitation function over the energy range Ec.m. = 0.3 - 1.3 MeV. We have identified and measured the properties of a newly observed level at Ex = 7.420 ± 0.014 MeV, which is most likely the mirror to the J? = 7/2+ 19F level at 7.56 MeV. We have additionally found a significant discrepancy with a recent compilation for the properties of a 19Ne state at Ex = 7.5 MeV and set upper limits on the proton widths of missing levels. © 2005 Elsevier B.V. All rights reserved.

4th International Conference on Exotic Nuclei and Atomic Masses -- SEP 12-16, 2004 -- -- Pine Mt, GA, WOS: 000233934000181, The rates of the F-18(p, alpha)O-15 and F-18(p, gamma) Ne-19 reactions in astrophysical environments depend on the properties of Ne-19 levels above the F-18 + p threshold. There are at least 8 levels in the mirror nucleus F-19 for which analogs have not been observed in Ne-19 in the excitation energy range E-x = 6.4-7.6 MeV. We have made a search for these levels by measuring the H-1(F-18, p)F-18 excitation function over the energy range Ec.m. = 0.3-1.3 MeV. We have identified and measured the properties of a newly observed level at E, = 7.420 +/- 0.014 MeV, which is most likely the mirror to the J(pi) = 7/2(+) F-19 level at 7.56 MeV. This new level is found to increase the calculated F-18(p,alpha)O-15 reaction rate by 16%, 63%, and 106% at T = 1,2, and 3 GK, respectively.

The degree to which the (p,γ) and (p,α) reactions destroy 18F at temperatures (1-4) × 108 K is important for understanding the synthesis of nuclei in nova explosions and for using the long-lived radionuclide 18F, a target of γ-ray astronomy, as a diagnostic of nova mechanisms. The reactions are dominated by low-lying proton resonances near the I8F+p threshold (Ex = 6.411 MeV in 19Ne). To gain further information about these resonances, we used a radioactive 18F beam from the Holifield Radioactive Ion Beam Facility to selectively populate corresponding mirror states in 19F via the inverse 2H(18F,p)19F neutron transfer reaction. Neutron spectroscopic factors were measured for states in 19F in the excitation energy range 0-9 MeV. Widths for corresponding proton resonances in 19Ne were calculated using a Woods-Saxon potential. The results imply significantly lower I8F(p,γ)19Ne and I8F(p,α)15O reaction rates than reported previously, thereby increasing the prospect of observing the 511 keV annihilation radiation associated with the decay of 18F in the ashes ejected from novae.

WOS: 000228643500003, The degree to which the (p, gamma) and (p, alpha) reactions destroy F-18 at temperatures (1-4) x 10(8) K is important for understanding the synthesis of nuclei in nova explosions and for using the long-lived radionuclide F-18, a target of gamma-ray astronomy, as a diagnostic of nova mechanisms. The reactions are dominated by low-lying proton resonances near the F-18+p threshold (E-x = 6.411 MeV in Ne-19). To gain further information about these resonances, we used a radioactive F-18 beam from the Holifield Radioactive Ion Beam Facility to selectively populate corresponding mirror states in F-19 via the inverse H-2((18)p)F-19 neutron transfer reaction. Neutron spectroscopic factors were measured for states in F-19 in the excitation energy range 0-9 MeV. Widths for corresponding proton resonances in Ne-19 were calculated using a Woods-Saxon potential. The results imply significantly lower F-18(p, gamma)Ne-19 and F-18(p, alpha)O-15 reaction rates than reported previously, thereby increasing the prospect of observing the 511 keV annihilation radiation associated with the decay of F-18 in the ashes ejected from novae.

WOS: 000223590600061, The rates of the F-18(p, alpha) O-15 and F-18(p, gamma) Ne-19 reactions in astrophysical environments depend on the properties of Ne-19 levels above the F-18+p threshold. There are at least eight levels in the mirror nucleus F-19 for which analogs have not been observed in Ne-19 in the excitation energy range E-x=6.4-7.6 MeV. These levels may significantly enhance the F-18+p reaction rates, and thus we have made a search for these levels by measuring the H-1(F-18,p) F-18 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(pi) = 7/2 + F-19 level at 7.56 MeV. We have additionally found a significant discrepancy with a recent compilation for the properties of a Ne-19 state at E-x=7.5 MeV and set upper limits on the proton widths of missing levels.

The astrophysical rate of the 18F(p,α)15O reaction at nova temperatures is critical to understanding production of the radioisotope 18F, which may be used to constrain nova models via observations with the coming generation of satellite-based γ-ray telescopes. As such, a measurement is made of the strength of this resonance using a radioactive 18F beam at the HRIBF. As a result, it is indicated that the 18F(p,α)15O reaction rate is lower than previous estimates by a factor of ∼2.

Knowledge of the astrophysical [Formula Presented] rate is important for understanding gamma-ray emission from novae and heavy-element production in x-ray bursts. A state with [Formula Presented] in [Formula Presented] provides an s-wave resonance and, depending on its properties, could dominate the [Formula Presented] rate. By measuring a kinematically complete [Formula Presented] excitation function with a radioactive [Formula Presented] beam at the ORNL Holifield Radioactive Ion Beam Facility, we find that the [Formula Presented] state lies at a center-of-mass energy of [Formula Presented] has a total width of [Formula Presented] and a proton partial-width of [Formula Presented].

Knowledge of the [Formula Presented] reaction rate is important for understanding stellar explosions, but it was uncertain because the properties of an expected but previously unobserved [Formula Presented] state in [Formula Presented] were not known. This state would provide a strong s-wave resonance for the [Formula Presented] system and, depending on its excitation energy, could dominate the stellar reaction rate at temperatures above 0.2 GK. We have observed this missing [Formula Presented] state by measuring the [Formula Presented] excitation function with a radioactive [Formula Presented] beam at the ORNL Holifield Radioactive Ion Beam Facility (HRIBF). We find that the state lies at a center-of-mass energy of [Formula Presented] keV [Formula Presented] and has a width of [Formula Presented] The measured properties of the resonance are only consistent with a [Formula Presented] assignment.

The 17F(p, γ)18 reaction is important in stellar explosions, but its rate has been uncertain because of an expected 3+ state in 18Ne that has never been conclusively observed. This state would provide a strong l = 0 resonance and, depending on its excitation energy, could dominate the stellar reaction rate. We have observed this missing 3+ state by measuring the 1H(17F, p)17F excitation function with a radioactive 17F beam at the ORNL Holifield Radioactive Ion Beam Facility. We find that the state lies at a center-of-mass energy of Er = 599.8 ± 1.5stat ± 2.0sys keV (Ex = 4523.7 ± 2.9keV) and has a width of Γ = 18 ± 2stat ± 1sys keV.