Search

We present the Internal Target Facility of the NIKHEF 900 MeV polarized electron storage ring. We give some results which illustrate the presently unique opportunity offered by this facility to study the spin structure of the nucleon, 2-body and 3-body system by the measurement of spin-dependent electron scattering observables.

The (e, e'd) reaction has been measured on 4 He, 6 Li, and 12 C. The theoretical description of this reaction is discussed both in a quasielastic cluster-knockout approach and in a microscopic approach. Results of these descriptions are compared with the measured (e, e'd) cross sections as a test of the deuteron-knockout mechanism and of the possibility of extracting nuclear-structure information. It is shown that a quasielastic approach is valid only in limiting cases like the 6 Li(e, e'd) reaction. The excitation of a T = 1 state in the 12 C(e, e'd) 10 B reaction can be described in the microscopic approach as a transition from a 1 S 0 pn cluster to a 3 S 1 deuteron. The form of the momentum distributions extracted from the data within a semi-microscopic approach, representing the motion of the pn cluster in the nucleus, is in global agreement with model calculations. However, the dependence of the measured cross sections as a function of momentum transfer is not well described, which results in a sizable uncertainty in the absolute normalization of the extracted momentum distributions.

Coincidence cross sections obtained with the (e, e′p) reaction are presented for the 4He nucleus. From the measurements, performed in non-parallel kinematics at a relative p-3H kinetic energy in the center-of-mass system of 75 MeV, the proton-triton momentum distribution for recoil momenta up to 350 MeV/c has been extracted. The results show a strong dependence on the kinematical configuration. In order to study this in more detail we extended the 4He(e,e′p)3H experiments to other kinematics, both parallel and non-parallel, and compare these data to phenomenological and microscopic calculations. The phenomenological treatment consists of a distorted-wave impulse approximation (DWIA) analysis using an optical potential. Charge-exchange effects in the final state are accounted for through coupled-channels calculations using the Lane formalism. These phenomenological calculations do not agree with the data. The microscopic calculation, which employs a diagrammatic treatment including the charge-exchange process (e, e′n)(n, p), proton rescattering effects and the contributions from meson-exchange currents, accounts fairly well for the empirical observations. The momentum dependence of the data is compared with theoretical calculations obtained with the VMC and ATMS variational methods for the Urbana and RSC nucleon-nucleon potentials. The results for the Urbana V14 NN potential, including corrections to PWIA using the microscopic model, are in good agreement with the data. The (e, e′n)(n, p) two-step contribution turns out to be an important ingredient for obtaining a satisfactory description of the 4He(e, e′p)3H cross sections. Sum-rule results are presented and the data are compared to results of (p, 2p) and other (e, e′p) experiments.

The differential cross section for excitation of the 1 + state at E x = 3.486 MeV in 88 Sr by inelastic electron scattering has been measured for values of the momentum transfer f between 0.22 and 2.57 fm −1 . Both nuclear core polarization and Δ -hole polarization seem to be necessary to describe the observed reduction of the B (M1) value and data at low q and the behaviour of the cross section at intermediate values of q .