A set of parameters has been derived for a global optical potential from elastic a-nucleus scattering with energies higher than 80 MeV. The geometry and energy dependence derived by Put and Paans was adopted. The optical model predictions were tested with data from elastic as well as from inelastic scattering.

Differential cross sections of elastic scattering of deuterons on the target nuclei 'Al, Y, ' Sn, and Pb were measured at Ed --58.7 MeV and Ed --85 MeV. "Best-fit" parameters in terms of the phenomenological optical model were extracted from the data including in addition differential cross section and analyzing power data from the literature. A set of global optical potential parameters is derived.

The search for a quasi bound η meson in atomic nuclei is reviewed. This tentative state is studied theoretically as well as experimentally. The theory starts from elastic η nucleon scattering which is derived from production data within some models. From this interaction the η nucleus interaction is derived. Model calculations predict binding energies and widths of the quasi bound state. Another method is to derive the η nucleus interaction from excitation functions of η production experiments. The s wave interaction is extracted from such data via final state interaction theorem. We give the derivation of s wave amplitudes in partial wave expansion and in helicity amplitudes and their relation to observables. Different experiments extracting the final state interaction are discussed as are production experiments. So far only three experiments give evidence for the existence of the quasi bound state: a pion double charge exchange experiment, an effective mass measurement, and a transfer reaction at recoil free kinematics with observation of the decay of the state.

We have studied the reaction p + 27 Al → 3 He + p + π − + X at recoil-free kinematics. An η meson possibly produced in this reaction would be thus almost at rest in the laboratory system and could therefore be bound with high probability, if nuclear η states exist. The decay of such a state through the N * (1535) resonance would lead to a proton-π − pair emitted in opposite directions.For these conditions we find some indication of such a bound state. An upper limit of ≈ 0.5 nb is found.

Energy and angular dependence of double differential cross sections d 2 σ/dΩdE was measured for reactions induced by 2.5 GeV protons on Au target with isotopic identification of light products (H, He, Li, Be, and B) and with elemental identification of heavier intermediate mass fragments (C, N, O, F, Ne, Na, Mg, and Al). It was found that two different reaction mechanisms give comparable contributions to the cross sections. The intranuclear cascade of nucleon-nucleon collisions followed by evaporation from an equilibrated residuum describes low energy part of the energy distributions whereas another reaction mechanism is responsible for high energy part of the spectra of composite particles. Phenomenological model description of the differential cross sections by isotropic emission from two moving sources led to a very good description of all measured data. Values of the extracted parameters of the emitting sources are compatible with the hypothesis claiming that the high energy particles emerge from pre-equilibrium processes consisting in a breakup of the target into three groups of nucleons; small, fast and hot fireball of ∼ 8 nucleons, and two larger, excited prefragments, which emits the light charged particles and intermediate mass fragments. The smaller of them contains ∼ 20 nucleons and moves with velocity larger than the CM velocity of the proton projectile and the target. The heavier prefragment behaves similarly as the heavy residuum of the intranuclear cascade of nucleon-nucleon collisions.

The energy and angular dependence of double differential cross sections d 2 σ/dΩdE were measured for p, d, t, 3,4 He, 6,7 Li, 7,9 Be, and 10,11 B produced in collisions of 0.175 GeV protons with Ni target. The analysis of measured differential cross sections allowed to extract total production cross sections for ejectiles listed above. The shape of the spectra and angular distributions indicate the presence of other nonequilibrium processes besides the emission of nucleons from the intranuclear cascade, and besides the evaporation of various particles from remnants of intranuclear cascade. These nonequilibrium processes consist of coalescence of nucleons into light charged particles during the intranuclear cascade, of the fireball emission which contributes to the cross sections of protons and deuterons, and of the break-up of the target nucleus which leads to the emission of intermediate mass fragments. All such processes were found earlier at beam energies 1.2, 1.9, and 2.5 GeV for Ni as well as for Au targets, however, significant differences in properties of these processes at high and low beam energy are observed in the present study.

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