[en] Radioactive ion beams of ¹⁷F were used to study several resonance states in ¹⁸Ne . Clear evidence for simultaneous two-proton emission from the 6.15MeV state (J^π=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

[en] Ion beam purity is of crucial importance to experimental research in nuclear structure and nuclear astrophysics at the Holifield Radioactive Ion Beam Facility (HRIBF). Mass selected beams are often mixtures of the radioactive isotope of interest and isobaric contaminants that complicate and sometimes compromise experiment. In order to maximize the use of the large radius magnetic mass separator at HRIBF for isobaric purification, the inherent energy spread of injected beams in the 25-MV tandem electrostatic accelerator must be minimized. The development of a negative ion beam cooler based on collisional cooling in a gas-filled RF ion guide has been reported to reduce negative ion beam spreads to a few eV. However, for some systems where magnetic separation is not sufficient, a novel technique based on selective non-resonant laser photodetachment inside the cooler has been developed. The interaction time of the laser radiation with the negative ions dramatically increases in the cooler, substantially increasing the efficiency of the selective photodetachment process. For example, due to a difference in the electron affinities of Co (0.661 eV) and Ni (1.156 eV), 2.5 W Nd:YAG laser radiation at 1.165 eV directed through the cooler achieved 95% suppression of 59Co- ions, while under identical conditions only 10% of 58Ni- ions were neutralized. Improvements in this proof-of-principle experiment and new results for O, F and S, Cl using laser radiation at 2.35 eV, are presented

[en] Sub-barrier fusion of ¹³²Sn and ⁶⁴Ni was measured at E_beam=465 MeV with an improved apparatus. The result of this new measurement is well reproduced by a coupled-channel calculation and a density-constrained time-dependent Hartree-Fock calculation. The previously measured cross section at E_beam=453 MeV was reanalyzed. Only an upper limit of the cross section was obtained

[en] The Holifield Radioactive Ion Beam Facility (HRIBF) is a national user facility for research with radioactive ion beams (RIBs) that has been in routine operation since 1996. It is located at Oak Ridge National Laboratory (ORNL) and operated by the ORNL Physics Division. The principal mission of the HRIBF is the production of high quality beams of shortlived radioactive isotopes to support research in nuclear structure physics and nuclear astrophysics. HRIBF is currently unique worldwide in its ability to provide neutron-rich fission fragment beams post-accelerated to energies above the Coulomb barrier for nuclear reactions. HRIBF produces RIBs by the isotope separator on-line (ISOL) technique using a particle accelerator system that consists of the Oak Ridge Isochronous Cyclotron (ORIC) driver accelerator, one of the two Injectors for Radioactive Ion Species (IRIS1 or IRIS2) production systems, and the 25-MV tandem electrostatic accelerator that is used for RIB post-acceleration. ORIC provides a light ion beam (proton, deuteron, or alpha) which is directed onto a thick target mounted in a target-ion source (TIS) assembly located on IRIS1 or IRIS2. Radioactive atoms that diffuse from the target material are ionized, accelerated, mass selected, and transported to the tandem accelerator where they are further accelerated to energies suitable for nuclear physics research. RIBs are transported through a beam line system to various experimental end stations including the Recoil Mass Spectrometer (RMS) for nuclear structure research, and the Daresbury Recoil Separator (DRS) for nuclear astrophysics research. HRIBF also includes two off-line ion source test facilities, one low-power on-line ISOL test facility (OLTF), and one high-power on-line ISOL test facility (HPTL). This paper provides an overview and status update of HRIBF, describes the recently completed $4.7M IRIS2 addition and incorporation of laser systems for beam production and purification, and discusses a proposed replacement of the ORIC driver accelerator.

[en] The time spreads of Mn ions produced by three-photon resonant ionization in a hot-cavity laser ion source are measured. A one-dimensional ion-transport model is developed to simulate the observed ion time structures. Assuming ions are generated with a Maxwellian velocity distribution and are guided by an axial electric field, the predictions of the model agree reasonably well with the experimental data and suggest that the ions are radially confined in the ion source and a substantial fraction of the ions in the transport tube are extracted.

[en] Gas stopping of reaction products has a key feature, fixed holdup time independent of element, making it possible to provide ion beams of essentially all element. Two classes of gas stopping have been developed over the last 40+ years, broadly classified as He Jet and Ion guide. A primary difference between these two techniques is the physical separation of the stopping cell and the ionization cell in the He Jet technique. In this paper we point out two applications of current interest where this physical separation is crucial: 1) ionization (ion beam intensity) is independent of primary beam intensity and 2) multiuser capability for accelerator facilities. Specific examples will be described.

[en] A resonant ionization laser ion source based on all-solid-state, tunable Ti:Sapphire lasers is being developed for the production of pure radioactive ion beams. It consists of a hot-cavity ion source and three pulsed Ti:Sapphire lasers operating at a 10 kHz pulse repetition rate. Spectroscopic studies are being conducted to develop ionization schemes that lead to ionizing an excited atom through an auto-ionization or a Rydberg state for numerous elements of interest. Three-photon resonant ionization of 12 elements has been recently demonstrated. The overall efficiency of the laser ion source measured for some of these elements ranges from 1 to 40%. The results indicate that Ti:Sapphire lasers could be well suited for laser ion source applications. The time structures of the ions produced by the pulsed lasers are investigated. The information may help to improve the laser ion source performance.

[en] The first investigation of the transverse emittance of a hot-cavity laser ion source based on all-solid-state Ti:sapphire lasers is presented. The emittances of ⁶³Cu ion beams generated by three-photon resonant ionization are measured and compared with that of the ⁶⁹Ga and ³⁹K ion beams resulting from surface ionization in the same ion source. A self-consistent unbiased elliptical exclusion method is adapted for noise reduction and emittance analysis. Typical values of the rms and 90% fractional emittances of the Cu ion beams at 20 keV energy are found to be about 2 and 8 π mm mrad, respectively, for the ion currents of 2-40 nA investigated. The emittances of the laser-produced Cu ion beams are smaller than those of the surface-ionized Ga and K ion beams.

[en] We have investigated the E1 strength function of ¹¹Be by Coulomb excitation and measurement of the subsequent projectile photon decay. The photons were measured in a wall of BaF₂ detectors. We have used the virtual photon method to extract the photabsorption cross section and hence the dipole strength function. We compare our findings with sum rule predictions. This is a first example of techniques we will extend to heavier mass nuclei

[en] This report describes the efforts made to develop a resonant-ionization laser ion source based on tunable Ti:sapphire lasers for nuclear physics and astrophysics research at Holifield Radioactive Ion Beam Facility. Three Ti:sapphire lasers have been upgraded with individual pump lasers to eliminate laser power losses due to synchronization delays. Ionization schemes for 14 elements have been obtained. Off-line studies show that the overall efficiency of the laser ion source can be as high as 40%. TaC surface coatings have been investigated for minimizing surface and bulk trapping of the atoms of interest.