Kirby W. Kemper

Coupling effects in the elastic scattering of the exotic nucleus 6He on protons

Abstract Cross sections for the elastic scattering of 6He radioactive nuclear beam on proton targets have been measured at 38.3 MeV/nucleon. With a view to test the ability of general optical potentials to reproduce the data for scattering of unstable nuclei, the present results, as well as other existing data for 6,8He, have been analyzed within the framework of the microscopic Jeukenne–Lejeune–Mahaux nucleon–nucleus potential. The angular distributions were found to be best reproduced by reducing the real part of the optical potential. This renormalization can be seen as a consequence of the complex polarization potential produced by the coupling to the continuum due to the weakly bound nature of the unstable nuclei. This effect can be simulated in a phenomenological analysis by a surface potential.

Elastic scattering of 4He from 6Li and 7Li at 12.0 to 18.5 MeV

Abstract An optical model analysis has been applied to measured angular distributions of elastic scattering of α-particles by 6 Li and 7 Li at several bombarding energies between 12.0 and 18.5 MeV. The optical model gives a good representation of the data when a target spin-orbit, V I · l , potential is included. With V I · l ≠ 0 , a large interaction radius, ≈ 3.5 fm, for the real potential is preferred over a smaller radius, ≈ 2.5 fm.

MoNA—The Modular Neutron Array

The Modular Neutron Array (MoNA), a highly efficient time-of-flight neutron detector, is being constructed for use at the National Superconducting Cyclotron Laboratory. The modular design of the detector provides significant flexibility and allows the bulk of the assembly and testing to be done by undergraduates at nine of the schools participating in the project.

Constraining the 6.05 MeV 0 + and 6.13 MeV 3 − Cascade Transitions in the C 12 ( α , γ ) O 16 Reaction Using the Asymptotic Normalization Coefficients

The 12C(α,γ)^16O reaction plays a fundamental role in astrophysics and needs to be known with accuracy better than 10%. Cascade γ transitions through the excited states of 16 O are contributing to the uncertainty. We constrained the contribution of the 0+ (6.05 MeV) and 3- (6.13 MeV) cascade transitions by measuring the asymptotic normalization coefficients for these states using the α-transfer reaction 6 Li(12C,d)^16O at sub-Coulomb energy. The contribution of the 0+ and 3- cascade transitions at 300 keV is found to be 1.96 ± 0.3 and 0.12 ± 0.04  keV b for destructive interference of the direct and resonance capture and 4.36 ± 0.45 and 1.44 ± 0.12  keV b for constructive interference, respectively. The combined contribution of the 0+ and 3- cascade transitions to the 12C(α,γ)16O reaction cross section at 300 keV does not exceed 4%. Significant uncertainties have been dramatically reduced.

Two-neutron knockout from neutron-deficient Ar-34, S-30, and Si-26

Department of Physics, School of Electronics and Physical Sciences,University of Surrey, Guildford, Surrey GU2 7XH, United Kingdom(Dated: February 8, 2008)Two-neutron knockout reactions from nuclei in the proximity of the proton dripline have beenstudied using intermediate-energy beams of neutron-deficient

A useful spectroscopic tool: The (7Li, 6He) reaction☆

Angular distribution measurements for the reactions 24Mg(7Li, 6He)25 Al and 52Cr(7Li, 6He)53 Mn atE(7Li) = 34 MeV show that for angles less than 15°, the shapes of the measured angular distributions allow d52 or d32, and f72 or f52 final-state configurations to be distinguished when compared with finite-range DWBA calculations.

High momentum transfer RT,L inclusive response functions for 3,4He.

Inclusive electron scattering cross sections for {sup 3,4}He have been measured in the quasielastic region at electron energies between 0.9 and 4.3 GeV, and scattering angles of 15{degree} and 85{degree}. Longitudinal ({ital R}{sub {ital L}}) and transverse ({ital R}{sub {ital T}}) response functions have been extracted using a Rosenbluth separation at constant {vert bar}{bold q}{vert bar} of 1.050 GeV/{ital c}. The ratio of the longitudinal to the transverse reduced response functions in the negative {ital y} region reaches unity.

Shell structure at N=28 near the dripline: Spectroscopy of Si-42, P-43, and S-44

Measurements of the N=28 isotones 42Si, 43P and 44S using one- and two-proton knockout reactions from the radioactive beam nuclei 44S and 46Ar are reported. The knockout reaction cross sections for populating 42Si and 43P and a 184 keV gamma-ray observed in 43P establish that the d_{3/2} and s_{1/2} proton orbits are nearly degenerate in these nuclei and that there is a substantial Z=14 subshell closure separating these two orbits from the d_{5/2} orbit. The increase in the inclusive two-proton knockout cross section from 42Si to 44S demonstrates the importance of the availability of valence protons for determining the cross section. New calculations of the two-proton knockout reactions that include diffractive effects are presented. In addition, it is proposed that a search for the d_{5/2} proton strength in 43P via a higher statistics one-proton knockout experiment could help determine the size of the Z=14 closure.

Quadrupole effects in the elastic scattering of 10B, 11B, and 12C by 27Al

Abstract Differences in the elastic differential cross section for 10,11 B + 27 Al at 50 MeV and 12 C + 27 Al at 55 MeV at back angles are attributed to expected quadrupole terms in the elastic scattering potentials. The theoretical results presented are based on a microscopic model.

Elastic scattering of deuterons by 6Li and 7Li at 8.0–12.0 MeV

Abstract Absolute differential cross sections for the elastic scattering of protons and deuterons by 6 Li and 7 Li have been measured with an error of ≈ 2% at selected angles and bombarding energies. The optical model is used to describe the angular distributions of the deuteron scattering at E d = 8.0, 10.0 and 12.0 MeV. The model parameters found when one uses a real potential radius between 3 fm and 4 fm are more nearly constant with changes in bombarding energy than are those obtained using a value ≈ 2 fm. The two sets of parameters represent a phase equivalent ambiguity.