The astrophysically important3+state in18Neand the

D. W. Bardayan

¹

,

J. C. Blackmon

²

,

C. R. Brune

³

et al.

Abstract

Knowledge of the 17 F(p,␥) 18 Ne reaction rate is important for understanding stellar explosions, but it was uncertain because the properties of an expected but previously unobserved 3 ϩ state in 18 Ne were not known. This state would provide a strong s-wave resonance for the 17 Fϩp system and, depending on its excitation energy, could dominate the stellar reaction rate at temperatures above 0.2 GK. We have observed this missing 3 ϩ state by measuring the 1 H( 17 F,p) 17 F excitation function with a radioactive 17 F beam at the ORNL Holifield Radioactive Ion Beam Facility ͑HRIBF͒. We find that the state lies at a center-of-mass energy of E r ϭ599.8 Ϯ1.5 stat Ϯ2.0 sys keV (E x ϭ4523.7Ϯ2.9 keV) and has a width of ⌫ϭ18Ϯ2 stat Ϯ1 sys keV. The measured properties of the resonance are only consistent with a J ϭ3 ϩ assignment.

Nuclear astrophysics with radioactive beams

“…Inverse-kinematics resonant proton scattering measurements have been performed, for example, with the thick-target technique at the TUDA facility at TRIUMF/ISAC, 21 Na + p [369,370] and 20 Na + p [371]; with the thin and thick-target approach at HRIBF/ORNL, 17 F + p [366,367] and 18 F + p [347,372]; at Louvain-la-Neuve with the thick-target technique, 13 [383]; as well as at Texas A&M [384,382], Notre Dame [385,386], ANL [387] and Spiral/GANIL [388].…”

“…In the thin-target approach, see for example [366,347,367], the energy region of interest is scanned by using beams at different energy. At ORNL, resonances in the compound nucleus 19 Ne were studied with a 18 F beam at 15 different energies between 10 and 14 MeV [347] irradiating a 35 µg/cm 2 CH 2 target. The scattered protons were detected in SIDAR and 18 F passing through the target was identified in an ionization chamber [347].…”

“…At ORNL, resonances in the compound nucleus 19 Ne were studied with a 18 F beam at 15 different energies between 10 and 14 MeV [347] irradiating a 35 µg/cm 2 CH 2 target. The scattered protons were detected in SIDAR and 18 F passing through the target was identified in an ionization chamber [347]. In the thick-target approach, the beam is slowed down and stopped in the target and the elastic proton scattering can be performed over a range of energies that depends on the choice of target thickness and beam energy.…”

“…The removal of two sectors from the complete annular LEDA detector allows the remaining six sectors to be arranged as a six-sided cone (referred to as the LAMP configuration) providing very large solid-angle coverage at poorer angular resolution [346]. ORNL's Silicon Detector Array (SIDAR) [347] consists of single-sided silicon strip detectors of the LEDAtype (128 strips each) and a smaller CD-like detector with 64 strips in total for the detection and identification of the heavy recoil [348,347]. The TRIUMF UK Detector Array (TUDA) facility at ISAC/TRIUMF is a cylindrical scattering chamber, where large-area silicon detectors of the LEDA-type or similar CD-shaped detectors can be mounted [349].…”

Advances in instrumentation for nuclear astrophysics

“…The jet nozzle can be fed directly from a gas cylinder, but as the gas throughput of such a system is large, a further refinement is to recollect the gas from the receiver and pumping stages, recompress it, and recirculate it through the nozzle in a continuous fashion. 18,21 Such an approach is critical to producing targets of rare or enriched gasses, such as 3 He. The JENSA gas target (Jet Experiments in Nuclear Structure and Astrophysics), 23,24 is a stateof-the-art recirculating gas-jet target, developed by a collaboration of physicists from Colorado School of Mines, Oak Ridge National Laboratory, Louisiana State University and Michigan State University.…”