Investigation of the23Na(p, γ)24Mg and 23Na(p, α)20Ne reactions via (3He,d) spectroscopy

States near the 23Na+p threshold in 24Mg were investigated using the 23Na(3He,d)24Mg reaction over the angular range of 5° ≤ θlab ≤ 35° at E(3He)=20 MeV. Spectroscopic factors were extracted for states corresponding to resonances in the 23Na(p, γ) 24Mg and 23Na(p, α)20Ne reactions. We find that one state, corresponding to a previously unobserved resonance at Ec.m.= 138 keV, may make a significant contribution to the rates of both reactions at low temperatures. Another state, corresponding to a possible resonance at Ec.m.=37 keV may make a small contribution to the 23Na(p, α)20Ne reaction. New rates for the 23Na(p, γ)24Mg and 23Na(p, α) 20Ne reactions are presented and the astrophysical implications are discussed

Measurement of the O17(p,α)N14 cross section at stellar energies

The cross section for the astrophysically important O17(p,α)N14 reaction was measured at proton energies of 75 and 65 keV. Thick, high-purity Ta2O5 targets (77% enriched O17) and large-area detectors were used with beam currents of 0.45 mA. Backgrounds were measured using Ta2O5 targets of natural isotopic composition. The expected resonance at Ep=70 keV was observed in the data taken at 75 keV, and its proton width was found to be 22± 3stat±2target -1beam+2 neV

Investigation of the 22Ne(p,y)23Na reaction via a (3He,d) spectroscopy

States near the [Formula Presented] threshold in [Formula Presented] were investigated using the [Formula Presented] reaction over the angular range of [Formula Presented] at [Formula Presented] Spectroscopic factors were extracted for states corresponding to resonances in the [Formula Presented] reaction. Two previously suggested resonances at [Formula Presented] and 100 keV were not observed at any angle. A new rate for the [Formula Presented] reaction has been calculated and its implications are discussed

First on-line results for As and F beams from HRIBF target/ion sources

The first on-line tests of the ion sources to provide radioactive ion beams of 69/7OAs and 17>18F for the Holifield Radioactive Ion Beam Facility have been performed using the UNISOR facility at HRIBF. For 70As the measured efficiency is 0.8+ 0.3% with a hold-up time of 3.6 ± 0.3 hours as measured with ^As at a target temperature of 1270°C. For 17F the efficiency for A117F is 0.0024 + 0.0008% with a hold-up time of 16.4 + 0.8 m as measured with A118F at a target temperature of 1470°C

Measurement of 7Li(n,γ0)8Li cross sections at En=1.5-1340 eV

The 7Li(n,γ)8Li cross section is important in inhomogeneous big bang models, and as a constraint on model parameters used to determine the solar 7Be(p,γ)8B reaction rate. Values of the 7Li(n,γ0)8Li reaction cross section were measured for neutron energies between 1.5 and 1340 eV at the Oak Ridge Electron Linear Accelerator. The normalization of the cross section was determined by measuring the gamma-ray yield from the 7Li(n,γ0)8Li reaction relative to that from the 10B(n,αγ)7Li reaction. The cross section was found to have the inverse neutron-velocity relationship (1/υ) indicative of s-wave capture. These results help resolve ambiguities in previous measurements

Strength of the 18F(p, α)15O resonance at Ec.m. = 330 keV

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

γ spectroscopy of states in Cl 32 relevant for the S 31 (p,γ) Cl 32 reaction rate

Background: The S31(p,γ)Cl32 reaction becomes important for sulfur production in novae if the P31(p,α)Si28 reaction rate is somewhat greater than currently accepted. The rate of the S31(p,γ)Cl32 reaction is uncertain, primarily due to the properties of resonances at Ec.m.=156 and 549 keV. Purpose: We precisely determined the excitation energies of states in Cl32 through high-resolution γ spectroscopy including the two states most important for the S31(p,γ)Cl32 reaction at nova temperatures. Method: Excited states in Cl32 were populated using the B10(Mg24,2n)Cl32 reaction with a Mg24 beam from the ATLAS facility at Argonne National Laboratory. The reaction channel of interest was selected using recoils in the Fragment Mass Analyzer, and precise level energies were determined by detecting γ rays with Gammasphere. Results: We observed γ rays from the decay of six excited states in Cl32. The excitation energies for two unbound levels at Ex=1738.1 (6) keV and 2130.5 (10) keV were determined and found to be in agreement with a previous high-precision measurement of the S32(He3,t)Cl32 reaction [1]. Conclusions: An updated S31(p,γ)Cl32 reaction rate is presented. With the excitation energies of important levels firmly established, the dominant uncertainty in the reaction rate at nova temperatures is due to the strength of the resonance corresponding to the 2131-keV state in Cl32

Neutron single particle strengths from the (d,p) reaction on F18

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

Destruction of 18F via 18F(p,α) 15O burning through the Ec.m.=665 keV resonance

Knowledge of the astrophysical rate of the 18F(p,α)15O reaction is important for understanding the γ-ray emission expected from novae and heavy-element production in x-ray bursts. The rate of this reaction is dominated at temperatures above ∼0.4 GK by a resonance near 7.08 MeV excitation energy in 19Ne. The 18F(p,α)15O rate has been uncertain in part because of disagreements among previous measurements concerning the resonance strength and excitation energy of this state. To resolve these uncertainties, we have made simultaneous measurements of the 1H(18F,p)18F and 1H(18F,α)15O excitation functions using a radioactive 18F beam at the ORNL Holifield Radioactive Ion Beam Facility. A simultaneous fit of the data sets has been performed, and the best fit was obtained with a center-of-mass resonance energy of 664.7±1.6 keV (Ex = 7076±2 keV), a total width of 39.0±1.6 keV, a proton branching ratio of Γp/Γ = 0.39±0.02, and a resonance strength of ωγ= 6.2±0.3 keV

New constraints on the18F(p,α)15O rate in novae from the (d, p) reaction

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