J. Gomez del Campo

Coulomb excitation of giant resonances in 208Pb by E = 84 MeV/Nucleon 17O projectiles

Abstract Inelastic scattering of 84 MeV/nucleon 17 O on 208 Pb has been measured between 1.5° ⩽ θ CM ⩽5.0°. The giant resonance structure near 12 MeV is excited with a differential cross section of more than 2b/sr and exhibits a peak-to-continuum ratio as large as 6 to 1. The major part of the cross section can be ascribed to Coulomb excitation of the isovector giant dipole and the giant quadrupole resonance. From the Coulomb excitation of the GQR we deduce a B (E2) fx = 0.53 ±0.11 e 2 b 2 which is that expected for a nearly pure isoscalar resonance which exhausts ≈ 60% of the EWSR.

Resonant-coherent excitation of channeled ions.

A first-principles calculation of the resonant-coherent excitation of planar-channeled hydrogenic ions is presented. The interplay between coherent interaction with the periodic crystal lattice potential and inelastic electron-electron collisions is shown to be crucial in both intraionic transitions and electron loss from the ion. The magnitude of resonant-coherent excitation is predicted to oscillate with the amplitude of the oscillations of the ion trajectory. Good agreement is found with experiments.

Resonant coherent excitation of O7+, F8+, and C5+ in the 〈100〉 axial channel in gold

Abstract Previous studies have shown that when an ion moves in an axial channel with a velocity, v , such that hKv/ d = ΔE ij , transitions are coherently induced. K is an integer, d is the longitudinal atomic spacing in the channel, and ΔE ij , is an ionic transition energy. Since the ionization cross section for an excited state is much greater than that for the ground state, the effect for 1s → 2p transitions is observed as a minimum in the surviving, one-electron charge-state fraction as the velocity is scanned through a resonance. Resonant coherent excitation (RCE) for the following one-electron ions, moving in the 〈100〉 axial channel in gold, are reported here: O 7+ , K = 2, 85.9 MeV; F 8+ , K = 2, 163.6 MeV; and C 5+ , K = 1, 81.6 MeV. The K = 2 resonances have a single narrow dip superimposed on a broad minimum, in contrast to the doublet minimum previously observed for lower Z ions. Comparison is made to predictions based on the positions of the Stark components deduced from the rainbow scattering theory. A similar comparison is made for the stronger and broader K = 1 resonance of C 5+ .

Fusion of radioactive Sn-132 with Ni-64

Evaporation residue and fission cross sections of radioactive 132Sn on 64Ni 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 132Sn+64Ni with respect to stable Sn+64Ni. A systematic comparison of evaporation residue cross sections for the fusion of even 112-124Sn and 132Sn with 64Ni is presented.

Study of resonant reactions with radioactive ion beams

Abstract A fast and efficient method to study (p,p) and (p,α) resonances with radioactive beams in inverse kinematics is described. It is based on the use of thick targets and large area double-sided silicon strip detectors (DSSDs) to detect the recoiling light-charged particles and to determine precisely their scattering angle. The first nuclear physics experiments with the technique have been performed recently at the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge with stable beams of 17 O and radioactive beams of 17 F . The high-quality resonance measurements obtained demonstrate the capabilities of the technique. Pure 17 F beams from HRIBF were produced by fully stripping the ions and separating the interfering and more abundant 17 O ions by the beam transport system. The removal of interfering isobars is one of the various common challenges to both accelerator mass spectrometry (AMS) and radioactive ion beam (RIB) production. Experiments done with RIBs will benefit from the use of the most efficient techniques for production, isobar separation, transport and detection.

Resonant coherent excitation in planar channeling

Abstract Planar channeled ions (velocity = ν ) experience a coherent periodic perturbation of frequency ν = υ / d , where d is the distance along the ion path between planes orthogonal to the channeling plane. The velocity at which a given RCE harmonic, ( l , k ), occurs is tuneable with θ. This additional degree of freedom allows the measurement of (1) velocity dependence of the static and dynamic ( (wake) field on the ion, and (2) coincidences in velocity for more than one resonance. Using the enhanced ionization technique, we report on RCE for N 5+ and N 6+ in (100) planar channeling in Au.

Production of very neutron-deficient isotopes near 100Sn via reactions involving light-particle and cluster emission

Abstract The production of very neutron-deficient isotopes near 100Sn has been investigated by using on-line mass separation of evaporation residues produced by heavy-ion induced complete-fusion reactions. We measured the cross sections for 99Cd, 100In, 101Sn and 102In via 58Ni+58Ni fusion reactions followed by cluster emission, and via 58Ni+50Cr fusion reactions accompanied by evaporation of protons, neutrons or α particles. Both types of reactions yield similar cross sections for the production of exotic nuclei near 100Sn. The data are discussed in comparison with results obtained from statistical-model calculations.

Systematics of back angle 12C scattering — the 12C + 20Ne and 12C + 24Mg systems

Abstract The back angle scattering of 20 Ne and 24 Mg ions from 12 C display structured excitation functions and oscillatory angular distributions. These measurements bridge the gap between the previously studied 12 C + 16 O and 12 C + 28 Si systems.

Elastic scattering and breakup of 17 F at 10 MeV/nucleon

Angular distributions of fluorine and oxygen produced from 170 MeV 17^F incident on 208^Pb were measured. The elastic scattering data are in good agreement with optical model calculations using a double-folding potential and parameters similar to those obtained from 16^O+208^Pb. A large yield of oxygen was observed near \theta_lab=36 deg. It is reproduced fairly well by a calculation of the (17^F,16^O) breakup, which is dominated by one-proton stripping reactions. The discrepancy between our previous coincidence measurement and theoretical predictions was resolved by including core absorption in the present calculation.

States in 24Mg populated by the 10B(16O, d)24Mg and 12C(16O, α)24Mg reactions☆

Abstract States in 24 Mg were populated by the 10 B( 16 O, d) and 12 C( 16 O, α) reactions. Excitation functions at 7° for many of the levels were measured for bombarding energies between 40 and 46 MeV for the 16 O + 12 C reaction, and from 44 to 46 MeV for the 16 O + 10 B reaction. The reactions appear to be predominantly due to compound nucleus formation, and general agreement was found comparing the measured cross sections with Hauser-Feshbach calculations. The experimental cross sections for the members of the K π = 0 + and 2 + rotational bands are particularly well reproduced by the calculations up through the 8 + states.