M. Marangoni

Photoreactions of 12C, 16O and 40Ca in self-consistent RPA theory: (II). Unpolarized (γ, p) and (γ, n) angular distributions below pion threshold

Abstract The (γ, p), (γ, n) and inverse capture reactions in 12 C, 16 O and 40 Ca below pion threshold have been analysed in the frame of a self-consistent RPA theory with a Skyrme force (Sk3). E1 and E2 transitions in LWA are present in the calculation. Thereby, EC linked by gauge invariance to the effective interaction are included in the predicted cross sections. Through an overall comparison with the available experimental data, we attain, in the present context, a good fit of data up to 80 MeV. The observed symmetric behaviour of (γ, p) and (γ, n) angular distributions is well reproduced. The role of nuclear correlations on the action of EC by gauge invariance is discussed.

Photoreactions of 16O in self-consistent RPA theory: (III). Polarized (γ, p) and (γ, n) angular distributions and inverse capture reactions below 60 MeV

Abstract Polarized 16 O(γ, p 0 ) and 16 O(γ, n 0 ) reactions below 60 MeV are analyzed in the framework of a self-consistent RPA theory with the Skyrme force Sk3. The calculations include dipole and quadrupole transitions in LWA. Asymmetries, polarizations and analyzing powers are calculated and compared with the available experimental data. Our aim is to show to what extent polarized results give additional information to that extracted from the unpolarized ones, both on the many-body structure of the nucleus and on the nature of the reaction mechanism at intermediate energies.

Collective excitations in 12C(e, e'p0) and 12C(e, e'n0) reactions at low momentum transfer

Abstract Predictions of coincidence 12 C(e, e′ x ) reactions at low momentum transfer are presented in a continuum self-consistent RPA theory with Skyrme forces. SK3 and SKM interactions are used. We investigate the role of different form factors and multipolarities in 12 C(e, e′p 0 ) and 12 C(e, e′n 0 ) angular distributions at forward and backward electron kinematics. The incident electron energy is E i = 126 MeV and ω = 22.5 MeV is the nuclear excitation energy. The sensitivity of 12 C(e, e′p 0 ) angular correlations in forward direction to monopole excitations is especially emphasized.

The one-nucleon energy continuum in RPA-SK3 40Ca(e, é) nuclear responses at q⩽550 MeV/c

Abstract Longitudinal and transverse nuclear responses on 40 Ca (e, e′) electron scattering have been calculated at q ⩽550 MeV/ c in self-consistent HF-SK3 and RPA-SK3 nuclear models with the full treatment of the one-nucleon energy continuum. We analyze the quenching phenomena of the charge response in terms of he RPA-SK3 nuclear dynamics. The isoscalar and isovector longitudinal currents, which fulfil the continuity equation with the Skyrme RPA hamiltonian density, are derived. The missing strength is located in the isoscalar channel.

Resonance and quasi-free electron scattering on 12C in self-consistent RPA theory

Abstract On the basis of a self-consistent RPA theory with a SK3 nucleon-nucleon force, the 12C(e,e) reaction is evaluated from particle threshold up to 100 MeV including both the giant resonance and the quasi-free scattering region. For momentum transfer q ≈ 1 fm−1, our results yield considerable electric and magnetic multipole strengths in the continuum above the giant resonances.

Giant resonance studies using the reaction (e, e′ γ)

Abstract We have calculated the electromagnetic decay of the giant resonance of 12 C following electroexcitation. The nuclear states have been described within the framework of a 1p-1h self-consistent continuum RPA using the Skyrme-3 effective interaction. The resonant amplitude adds coherently with the electronic bremsstrahlung amplitude, which leads to angular distributions dominated by the bremsstrahlung peaks in the direction of the incident and scattered electron. In order to suppress the bremsstrahlung background and to enhance the resonant amplitude, the experiments should be performed at high energy of the incident electron, relatively small momentum transfer and for non-coplanar kinematics. In this kinematical region the predicted cross sections are of the order of 10 −32 cm 2 MeV · sr 2 with a suppression of bremsstrahlung by about one order of magnitude over a wide angular range.

The RPA nuclear continuum in16O(e, e′) reactions at low momentum transfer decay on (e, e′p) and (e, e′n) reaction channels

A theoretical investigation has been performed of16O(e, e′) and16O(e, e′x) reactions at low momentum transfer in the frame of a self-consistent HF and RPA theory with a SK3 interaction. Nuclear responses and their multipole components have been calculated in the whole energy-range for the two electron kinematicsi) ɛi=67 MeV and θ=40°,ii) ɛi=130 MeV and θ=50°. The microscopic structure of HF and RPA resonating states in the energy continuum has been inferred from the calculation. Decay properties in the reaction channels (e, e′p) and (e, e′n) have been discussed in the two cases of a semidirect and a knockout reaction process.

12C(e, e′ p) missing momentum distributions in HF-Sk3 and RPA-Sk3 continuum theories

We study the momentum distribution or reduced cross-section for electron induced 1p3/2 proton knockout from12C in parallel kinematics. We refer to continuum self-consistent HF-Sk 3 and RPA-Sk 3 theories with a full treatment of the one-nucleon energy continuum. The PWIA limit is also shown. The12C(e, e′p0) missing momentum distribution is analyzed in connection with the energy dependence at fixed momentum transfer of the12C(e, e′) longitudinal and transverse responses. We compare our theoretical results with the available experimental data.

Charge transition densities for the excitation and nucleon decay of the giant dipole resonance in16O

Predictions on charge transition densities in16O for the excitation of the giant dipole resonance are given within a continuum self-consistent RPA-SK3 theory. The nuclear states are allowed to decay with proton or neutron ejection. The discussion is focused on the analysis of the radial behaviour of transition densities in terms of their microscopic structure. The rôle of RPA ground state correlations is clarified. The surface properties of resonant nuclear states extracted from photonuclear and (e, e′ x) reactions at low momentum transfer are confronted with the full radial dependence of the resonant structure shown in charge transition densities.