An estimate of the average freeze-out volume for multifragmentation events is presented. Values of volumes are obtained by means of a simulation using the experimental charged product partitions ...measured by the 4π multidetector INDRA for 129Xe central collisions on natSn at 32 AMeV incident energy. The input parameters of the simulation are tuned by means of the comparison between the experimental and simulated velocity (or energy) spectra of particles and fragments.
Kinetic energy spectra and fragment velocity correlations, simulated by means of stochastic mean-field calculations, are successfully confronted with experimental data for single multifragmenting ...sources prepared at the same excitation energy per nucleon in 32
A MeV
129Xe
+
natSn and 36
A MeV
155Gd
+
natU central collisions. Relying thus on simulations, average freeze-out times of 200–240 fm/
c are estimated. The corresponding spatial distributions of fragments are more compact for the lighter system (
∼
3
–
4
V
0
vs.
∼
8
V
0
).
The blocking technique in single crystals has been applied to reaction time measurements for the $^{238}$U + Ge system at 6.1 MeV/nucleon. Backed up with a reaction mechanism analysis using the INDRA ...4$\pi$ detector, it provides a direct experimental evidence for Z = 124 compound nuclei living longer than 10−18s, indicating thus very high fission barriers for this element.
The residual nuclei produced in the spallation reaction of Xe-136 nuclei at 200A MeV on protons have been studied by measuring the isotopic distributions for the elements from cadmium (Z = 48) to ...cesium (Z = 55) by using the fragment separator (FRS) spectrometer at GSI and the inverse kinematics technique. This is one of the few measurements performed at such a low projectile energy, close to the validity limit for intranuclear cascade models such as INCL or ISABEL. The experimental results have been compared to these intranuclear cascade codes coupled to the evaporation code ABLA. Both code combinations reproduce qualitatively the measured isotopic distributions; however, both underestimate the production of residues with mass numbers between 126 and 134. The measured cross sections are of interest for the planning of future radioactive beam or neutron source facilities.
The intranuclear cascade (INC)+evaporation model is used to display the gross features of proton, neutron and deuteron induced spallation reactions between 200 MeV and 2 GeV incident energy per ...nucleon. Particular attention is focused on average particle multiplicities and their dependencies upon target mass number and incident energy. Simple formulae are derived to allow an easy use of these results. They are expected to provide a rapid survey of the gross features of spallation reactions. The decomposition of particle multiplicities and of cross-sections into cascade and evaporation components is performed and discussed. The impact parameter dependence is investigated. The excitation energy left in the target at the end of the cascade step is also studied, as well as the gross properties of the subsequent evolution of the target remnant. It is shown that neutron differential cross-sections can be split into components with reasonably identified physical origin, which exhibit simple power laws as functions of the target mass number.
In nuclear and atomic experiments at high incident ion energies, 20
MeV/
u
<
E
<
100
MeV/
u, the impact of swift heavy ions on thin solid targets is a source of fast electrons. The knowledge of their ...spatial and kinematical distributions is very useful for experimental nuclear and radiobiological applications as well as testing atomic ionization theories. An overview on the main mechanisms underlying the production of the electrons is given. Some recent results obtained at the Catania LNS superconducting cyclotron, mainly with a 45
MeV/
u
58Ni
19+ beam are shown. In particular, the production and the properties of binary encounter-, convoy-, in-flight Auger- and backward emitted electrons are discussed.
The N/Z dependence of projectile fragmentation at relativistic energies has been studied with the ALADIN forward spectrometer at the GSI Schwerionen Synchrotron (SIS). Stable and radioactive Sn and ...La beams with an incident energy of 600 MeV per nucleon have been used in order to explore a wide range of isotopic compositions. For the interpretation of the data, calculations with the statistical multifragmentation model for a properly chosen ensemble of excited sources were performed. The parameters of the ensemble, representing the variety of excited spectator nuclei expected in a participant-spectator scenario, are determined empirically by searching for an optimum reproduction of the measured fragment-charge distributions and correlations. An overall very good agreement is obtained. The possible modification of the liquid-drop parameters of the fragment description in the hot freeze-out environment is studied, and a significant reduction of the symmetry-term coefficient is found necessary to reproduce the mean neutron-to-proton ratios /Z and the isoscaling parameters of Z{<=}10 fragments. The calculations are, furthermore, used to address open questions regarding the modification of the surface-term coefficient at freeze-out, the N/Z dependence of the nuclear caloric curve, and the isotopic evolution of the spectator system between its formation during the initial cascade stage of the reaction and its subsequent breakup.
Insulating (MYLAR), semi-insulating (MYLAR-Au) and conducting foils have been bombarded by very energetic 64 MeV u
−1
78
Kr
32+
ions. The velocity spectra of fast electrons emitted in the backward ...and forward directions have been measured and analyzed as a function of the elapsed time in the run. A shift of binary encounter and convoy electrons emitted in the forward direction toward lower velocities has been observed with insulating targets. No such shift occurs with metallic targets. The surface potential evolves with time (i.e. ion fluence) both at forward and backward emission angle. It is shown that strong bulk charging of insulating targets leads to a positive potential as high as 9 kV before charge breakdown.
Spallation residues and fission fragments from 1A GeV 238U projectiles irradiating a liquid hydrogen target were investigated by using the fragment separator at GSI for magnetic selection of reaction ...products including ray-tracing, energy-loss and time-of-flight techniques. The longitudinal-momentum spectra of identified fragments were analyzed, and evaporation residues and fission fragments could be separated. For 1385 nuclides, production cross sections down to values of 10 microb with a mean accuracy of 15%, velocities in the uranium rest frame and kinetic energies were determined. In the reaction all elements from uranium to nitrogen were found, each with a large number of isotopes.
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