Multiple emission of intermediate-mass fragments has been studied for the collisions of p, 4 He and 12 C on Au with the 4π setup FASA. The mean IMF multiplicities (for the events with at least one IMF) are saturating at the value of 2.2 ± 0.2 for the incident energies above 6 GeV. The observed IMF multiplicities cannot be described in a two-stage scenario, a fast cascade followed by a statistical multifragmentation. Agreement with the measured IMF multiplicities is obtained by introducing an intermediate phase and modifying empirically the excitation energies and masses of the remnants.The angular distributions and energy spectra from the p-induced collisions are in agreement with the scenario of "thermal" multifragmentation of a hot and diluted target spectator. In the case of 12 C+Au(22.4 GeV) and 4 He(14.6 GeV)+Au collisions, deviations from a pure thermal break-up are seen in the energy spectra of the emitted fragments, which are harder than those both from model calculations and from the measured ones for p-induced collisions. This difference is attributed to a collective flow.

Saturation effects affecting absorption and fluorescence spectra of an atomic vapor confined in an Extremely Thin Cell (cell thickness L < 1µm) are investigated experimentally and theoretically. The study is performed on the D2 line (λ = 852nm) of Cs and concentrates on the two situations L = λ/2 and L = λ, the most contrasted ones with respect to the length dependence of the coherent Dicke narrowing. For L = λ/2, the Dicke-narrowed absorption profile simply broadens and saturates in amplitude when increasing the light intensity, while for L = λ, sub-Doppler dips of reduced absorption at line-center appear on the broad absorption profile. For a fluorescence detection at L = λ, saturation induces narrow dips, but only for hyperfine components undergoing a population loss through optical pumping. These experimental results are interpreted with the help of the various existing models, and are compared with numerical calculations based upon a two-level modelling that considers both a closed and an open system.

No abstract

Multiple emission of intermediate-mass fragments has been studied for the collisions p + Au at 2.16, 3.6 and 8.1 GeV with the FASA setup. The mean IMF multiplicities for events with at least one IMF are equal to 1.7, 1.9 and 2.1 (±0.2) respectively. The multiplicity, charge distributions and kinetic energy spectra of IMF are described in the framework of a intranuclear cascade model followed by the statistical multifragmentation model. However, between the two parts of the calculation the excitation energies and the residual masses and charges are modified to take into account the losses during expansion. The results support a scenario of true thermal multifragmentation of a hot and expanded target spectator.