T.W. O'Donnell

Transfer and/or Breakup Modes in The He-6+Bi-209 Reaction Near the Coulomb Barrier

Reaction products from the interaction of 6He with 209Bi have been measured at energies near the Coulomb barrier. A 4He group of remarkable intensity, which dominates the total reaction cross section, has been observed. The angular distribution of the group suggests that it results primarily from a direct nuclear process. It is likely that this transfer and/or breakup channel is the doorway state that accounts for the previously observed large sub-barrier fusion enhancement in this system.

An apparatus for applying strong longitudinal magnetic fields to clinical photon and electron beams

Monte Carlo studies have recently renewed interest in the use of the effect of strong transverse and longitudinal magnetic fields to manipulate the dose characteristics of clinical photon and electron beams. A 3.5 T superconducting solenoidal magnet was used to evaluate the effect of a longitudinal field on both photon and electron beams. This note describes the apparatus and demonstrates some of the effects on the beam trajectory and dose distributions for measurements in a homogeneous phantom. The effects were studied using film in air and in phantoms which fit in the magnet bore. The magnetic field focused and collimated the electron beams. The converging, non-uniform field confined the beam and caused it to converge with increasing depth in the phantom. Due to the fields collecting and focusing effect, the beam flux density increased, leading to increased dose deposition near the magnetic axis, especially near the surface of the phantom. This study illustrates some benefits and challenges associated with the use of non-uniform longitudinal magnetic fields in conjunction with clinical electron and photon beams.

Nuclear and Coulomb Interaction in 8B Breakup at Sub-Coulomb Energies

The angular distribution for the breakup of 8B-->7Be+p on a 58Ni target has been measured at an incident energy of 25.75 MeV. The data are inconsistent with first-order theories but are remarkably well described by calculations including higher-order effects. The comparison with theory illustrates the importance of the inclusion of the exotic proton halo structure of 8B in accounting for the data.

Nuclear and Coulomb Interaction in the 8B to 7Be + p Breakup Reaction at sub-Coulomb Energies

The angular distribution for the breakup of 8B-->7Be+p on a 58Ni target has been measured at an incident energy of 25.75 MeV. The data are inconsistent with first-order theories but are remarkably well described by calculations including higher-order effects. The comparison with theory illustrates the importance of the inclusion of the exotic proton halo structure of 8B in accounting for the data.

REACTION CROSS SECTIONS IN SI OF LIGHT PROTON-HALO CANDIDATES 12N AND 17NE

Abstract Total reaction cross sections, σ R , on Si were measured near 40 A MeV for the proton-halo candidate 12 N and the two-proton-halo candidate 17 Ne, and were compared with σ R for other light proton-rich nuclei. The A -dependence shows enhanced σ R s for 12 N and 17 Ne, relative to their neighbors, but the effect is smaller than for 8 B which has been argued to have a proton halo. In general, nuclei with loosely bound last protons ( S p ⩽ 1.5 MeV) have significantly larger σ R s than their neighbors. Cross sections for charge-removal from 12 N and 17 Ne also were obtained.

Gamma-ray spectroscopy with a low-energy 6He radioactive ion beam

Abstract A gamma-ray spectroscopy program has been established at the University of Notre Dame using a low-energy radioactive beam of 6 He for fusion–evaporation reactions. There are many experimental difficulties to overcome in the design of any such facility, most notably the large neutron flux associated with producing the secondary beam. Solutions to the problems are discussed and illustrated with the reaction 6 He + 63 Cu .

Installation and in-beam tests of a large-bore 7 T superconducting solenoid reaction-product collector

Abstract We have constructed and installed at the Michigan State University National Superconducting Cyclotron Laboratory a 40 cm bore, 1 m long, superconducting solenoid ( B oz ≈ 7 T) for use as a large-solid-angle reaction-product collector lens. The device has been used to produce short-lived isomeric secondary beams and very neutron-rich nuclei ( A = 40–80). These initial tests and the magnets performance are described.

Searching for resonance in the unbound 6Be and 5Li nuclei

Abstract Resonances in 6Be and 5Li have been investigated by deuteron transfer reactions with radioactive ion beams, 2H(8B,α)6Be, 2H(7Be,α)5Li, respectively. There is an indication of a possible resonance at excitation energy of 9.6 MeV in 6Be, just below the 3He+3He threshold. The structure of the 6Li nucleus has been also investigated by the neutron transfer reaction 3He(7Li,α)6Li. In 6Li, a new resonance is observed at about 12.4 MeV in excitation energy and the presence of a resonance at 15.2 MeV is confirmed. The data are preliminary and a detailed analysis is in progress. The instalation of a Radioactive Ion Beam facility in Brazil (RIBRAS) is also reported.

UNUSUAL ENERGY-DEPENDENCE OF THE TOTAL NUCLEAR-REACTION CROSS-SECTION FOR A SECONDARY ISOMERIC NUCLEAR BEAM (F-18(M), J(PI)=5(+), E(X)=1.1 MEV)

A primary O-17 beam has been used to produce a 22.3 MeV/nucleon F-18(m) isomeric secondary beam via a single nucleon transfer reaction on a carbon target. The total nuclear reaction cross sections for F-18(m) and F-18(g.s.) in silicon were measured in a stack of seven silicon solid-state detectors. The cross section for F-18(m) exhibits some unusual features at low energy not seen for F-18(g.s.) or other ions.