Microscopic Nuclear Structure and Reaction Calculations in the FMD Approach

Fermionic Molecular Dynamics (FMD) is a microscopic many-body approach which has been used successfully to study the structure of light nuclei in the pand sd-shell. FMD uses a Gaussian wave packet basis which contains the harmonic oscillator shell model and Brink-type cluster model wave functions as limiting cases. A realistic effective interaction that has been derived from the Argonne V18 interaction by treating explicitly short-range central and tensor correlations is employed. We present here a first application of the FMD approach to low-energy nuclear reactions, namely the 3He(α ,γ)7Be radiative capture reaction. We divide the Hilbert space into an external region where the system is described as 3He and 4He clusters interacting only via the Coulomb interaction and an internal region where the nuclear interaction will polarize the clusters. Polarized configurations are obtained by a variation after parity and angular momentum projection procedure with respect to the parameters of all single particle states. A constraint on the radius of the intrinsic many-body state is employed to obtain polarized clusters at desired distances. The boundary conditions for bound and scattering states are implemented using the Bloch operator. The FMD calculations reproduce the correct energy for the centroid of the 3/2 and 1/2 bound states in 7Be. The charge radius of the ground state is in good agreement with recent experimental results. The FMD calculations also describe well the experimental phase shift data in the 1/2+, 3/2 and 5/2 channels that are important for the capture reaction at low energies. Using the bound and scattering many-body wave functions we calculate the radiative capture cross section. The calculated S factor agrees very well, both in absolute normalization and energy dependence, with the recent experimental data from the Weizmann, LUNA, Seattle and ERNA experiments.