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The three-body breakup 6 He→ 4 Heϩnϩn is studied experimentally, using a secondary 6 He ion beam of 240 MeV/nucleon incident on carbon and lead targets. Integrated cross sections for one-and two-neutron knockout and differential cross sections d/dE* and d/d for inelastic nuclear or electromagnetic excitations into the 6 He continuum are presented. The E1-strength distribution is deduced from electromagnetic cross sections and is found to exhaust (10Ϯ2)% of the energy-weighted Thomas-Reiche-Kuhn sum rule or (40Ϯ8)% of the cluster sum rule for excitation energies below 5 MeV. Both the energy-weighted and non-energy-weighted dipole cluster sum rules are almost exhausted integrating the strength up to 10 MeV, a fact from which the root-mean-square distance between the ␣ core and the two valence neutrons of r ␣Ϫ2n ϭ(3.36Ϯ0.39) fm is derived. The known I ϭ2 ϩ ͑1.80 MeV͒ resonance in 6 He is observed in nuclear inelastic scattering; model-dependent values of the quadrupole deformation parameter ␦ 2 ϭ(1.7Ϯ0.3) fm or B(E2,0 ϩ →2 ϩ )ϭ(3.2Ϯ0.6)e 2 fm 4 are derived. No clear signature could be obtained for predicted higherlying 2 ϩ resonances, but low-lying continuum strength of multipolarity other than dipole, likely of monopole and quadrupole multipolarity, is indicated by the data. Two-body correlations in the decaying 4 Heϩnϩn system are investigated. The astrophysical relevance of the data with regard to the two-neutron capture process 4 He(2n,␥) 6 He is briefly discussed.

Multi-fragment decays of 129 Xe, 197 Au, and 238 U projectiles in collisions with Be, C, Al, Cu, In, Au, and U targets at energies between E/A = 400 MeV and 1000 MeV have been studied with the ALADIN forward-spectrometer at SIS. By adding an array of 84 SiCsI(Tl) telescopes the solid-angle coverage of the setup was extended to θ lab = 16 • . This permitted the complete detection of fragments from the projectile-spectator source.The dominant feature of the systematic set of data is the Z bound universality that is obeyed by the fragment multiplicities and correlations. These observables are invariant with respect to the entrance channel if plotted as a function of Z bound , where Z bound is the sum of the atomic numbers Z i of all projectile fragments with Z i ≥ 2. No significant dependence on the bombarding energy nor on the target mass is observed. The dependence of the fragment multiplicity on the projectile mass follows a linear scaling law.The reasons for and the limits of the observed universality of spectator fragmentation are explored within the realm of the available data and with model studies. It is found that the universal properties should persist up to much higher bombarding energies than explored in this work and that they are consistent with universal features exhibited by the intranuclear cascade and statistical multifragmentation models.

HADES is a versatile magnetic spectrometer aimed at studying dielectron production in pion, proton and heavy-ion induced collisions. Its main features include a ring imaging gas Cherenkov detector for electron-hadron discrimination, a tracking system consisting of a set of 6 superconducting coils producing a toroidal field and drift chambers and a multiplicity and electron trigger array for additional electron-hadron discrimination and event characterization. A two-stage trigger system enhances events containing electrons. The physics program is focused on the investigation of hadron properties in nuclei and in the hot and dense hadronic matter. The detector system is characterized by an 85 % azimuthal coverage over a polar angle interval from 18• to 85• , a single electron efficiency of 50 % and a vector meson mass resolution of 2.5 %. Identification of pions, kaons and protons is achieved combining time-of-flight and energy loss measurements over a large momentum range. This paper describes the main features and the performance of the detector system.