Isotopic effects in the fragmentation of excited target residues following collisions of 12C on (112,124)Sn at incident energies of 300 and 600 MeV per nucleon were studied with the INDRA 4pi ...detector. The measured yield ratios for light particles and fragments with atomic number Z < or = 5 obey the exponential law of isotopic scaling. The deduced scaling parameters decrease strongly with increasing centrality to values smaller than 50% of those obtained for the peripheral event groups. Symmetry-term coefficients, deduced from these data within the statistical description of isotopic scaling, are near gamma = 25 MeV for peripheral and gamma < 15 MeV for central collisions.
Directed and elliptic flow for the Au + Au system at incident energies between 40 and 150 MeV per nucleon has been measured using the INDRA 4 pi multi-detector. For semi-central collisions, the ...elliptic flow of Z <= 2 particles switches from in-plane to out-of-plane enhancement at around 100 MeV per nucleon, in good agreement with the result reported by the FOPI Collaboration. The directed flow changes sign at a bombarding energy between 50 and 60 MeV per nucleon and remains negative at lower energies. The conditions for the appearance and possible origins of negative flow are discussed.
Invariant cross sections of intermediate mass fragments in peripheral collisions of 197Au on 197Au at incident energies between 40 and 150 MeV per nucleon have been measured with the 4π ...multi-detector INDRA. The maximum of the fragment production is located near mid-rapidity at the lower energies and moves gradually towards the projectile and target rapidities as the energy is increased. Schematic calculations within an extended Goldhaber model suggest that the observed cross section distributions and their evolution with energy are predominantly the result of the clustering requirement for the emerging fragments and of their Coulomb repulsion from the projectile and target residues. The quantitative comparison with transverse energy spectra and fragment charge distributions emphasizes the role of hard scattered nucleons in the fragmentation process.
Correlation functions, constructed from directional projections of the relative velocities of fragments, are used to determine the shape of the breakup volume in coordinate space. For central ...collisions of 129Xe+natSn at 50 MeV per nucleon incident energy, measured with the 4π multidetector INDRA at GSI, a prolate shape aligned along the beam direction with an axis ratio of 1:0.7 is deduced. The sensitivity of the method is discussed in comparison with conventional fragment–fragment velocity correlations.
We study the anisotropy effects measured with INDRA at GSI in central collisions of
129Xe+
natSn at 50
A
MeV and
197Au+
197Au at 60, 80, 100
A
MeV incident energy. The microcanonical ...multifragmentation model with non-spherical sources is used to simulate an incomplete shape relaxation of the multifragmenting system. This model is employed to interpret observed anisotropic distributions in the fragment size and mean kinetic energy. The data can be well reproduced if an expanding prolate source aligned along the beam direction is assumed. An either non-Hubblean or non-isotropic radial expansion is required to describe the fragment kinetic energies and their anisotropy. The qualitative similarity of the results for the studied reactions suggests that the concept of a longitudinally elongated freeze-out configuration is generally applicable for central collisions of heavy systems. The deformation decreases slightly with increasing beam energy.
Energy spectra for intermediate mass fragments produced in central Au+Au collisions at E/A=100 MeV indicate a collective expansion at breakup. For the first time, values for this collective expansion ...energy per nucleon are extracted independently for each charge. Typically, these values are one-third to one-half of the incident kinetic energy per nucleon in the cm system, but they decrease with Z sub , suggesting that all fragments do not participate equally in the collective expansion.
Multi-fragment decays of
129Xe,
197Au and
238U projectiles in collisions with Be, C, Al, Cu, In, Au and U targets at energies between
E
A
= 400
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.
INDRA@GSI: collective flow in Au+Au collisions Łukasik, J; Trautmann, W; Auger, G ...
Progress in Particle and Nuclear Physics,
2004, Letnik:
53, Številka:
1
Journal Article, Conference Proceeding
Recenzirano
Directed flow in symmetric heavy ion collisions has been studied using the
197Au+
197Au reactions at incident energies between 40 and 150 A MeV. The reactions have been measured with the 4
π ...multi-detector INDRA at the GSI facility. In particular, the bombarding energy at which the elliptic flow switches from in-plane to out-of-plane enhancement has been determined to be clearly above 100 A MeV in good agreement with the result obtained by the FOPI Collaboration. The new data also allows to extend the experimental excitation function of
v
2 to lower energies.
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