M. Y. Lee

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.

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 .

Twinsol: A dual superconducting solenoid system for low-energy radioactive nuclear beam research

A unique type of apparatus is currently under construction as part of an upgrade to the radioactive ion beam facility at the University of Notre Dame Nuclear Structure Laboratory. The device will consist of a pair of large in-line superconducting solenoids (B0=6 tesla, bore=30 cm) which will be used to produce, collect, transport, focus and analyze both stable and radioactive nuclear beams. This apparatus in conjunction with the recently upgraded accelerators at Notre Dame is especially well suited for the production and utilization of intense (viz. >106/sec), low-energy (1–10 MeV/u), stable and radioactive nuclear beams relevant to the study of reactions involved in astrophysical processes. These improvements will allow for the production of radioactive beams of greater intensity, higher purity and at both higher and lower energies than previously available at this facility. The first phase of construction and results of initial tests will be reported.

Investigation of 8B structure at low excitation energies

The 7Be(p,γ)8B reaction plays a very important role in nuclear astrophysics, since it is the source of the high-energy solar neutrinos. However, it is not possible to measure the cross section of this reaction at solar energies (20 keV) directly so one must rely on extrapolations from higherenergy data. It is clear, that extrapolation procedure can be strongly influenced by higher lying broad resonances [1]. This makes knowledge of the structure of 8B nucleus crucial for the correct interpretation of the results of the direct radiative capture measurements.

Direct measurement of the L/K ratio in the electron capture decay of 7Be with cryogenic micro-calorimeters

Using a cryogenic micro-calorimeter originally developed for x-ray astrophysics, we have the performed the first direct investigation of the L/K capture ratio in 7Be electron capture decay. The low background and excellent energy resolution clearly resolve capture from the individual shells, resulting in a direct determination of the L/K ratio.Using a cryogenic micro-calorimeter originally developed for x-ray astrophysics, we have the performed the first direct investigation of the L/K capture ratio in 7Be electron capture decay. The low background and excellent energy resolution clearly resolve capture from the individual shells, resulting in a direct determination of the L/K ratio.