[en] The universal theory of order parameter fluctuations (Δ-scaling laws) is applied to a wide range of intermediate energy heavy-ion collision data obtained with INDRA. This systematic study confirms that the observed fragment production is compatible with aggregation scenarios for in- or out-of-equilibrium continuous phase transitions, while not showing any sign of critical behaviour or phase coexistence. We stress the importance of the methodology employed in order to gain further insight into the mechanism(s) responsible. (authors)

[en] Fragment production in central collisions of Xe+Sn has been systematically studied with the INDRA multidetector from 25 to 150 AMeV. The predominant role of collision dynamics is evidenced in multiple intermediate mass fragment production even at the lowest energies, around the so-called multifragmentation threshold. For beam energies 50 AMeV and above, a promising agreement with suitably modified Anti-symmetrized Molecular Dynamics calculations has been achieved. Intriguingly the same reactions have recently been interpreted as evidence for a liquid-gas phase transition in thermodynamically equilibrated systems. The universal fluctuation theory, thanks to its lack of any equilibrium hypothesis, shows clearly that in all but a tiny minority of carefully-selected central collisions fragment production is incompatible with either critical or phase coexistence behaviour. On the other hand, it does not exclude some similarity with aggregation scenarios such as the lattice-gas or Fisher droplet models. (authors)

[en] Characteristics of the primary fragments produced in central collisions of Xe + Sn system from 32 to 50 AMeV have been deduced. By using the relative velocity correlation technique between the light charged particles (LCP) and detected fragments, we were able to extract the multiplicities and average kinetic energy of the secondary evaporated LCP. We then reconstructed the size and excitation energy of the primary fragments. For each bombarding energy a constant value of the excitation energy per nucleon, over the whole range of fragment charge has been found, suggesting that on the average thermodynamical equilibrium has been achieved at the freeze-out. This value increases slightly from 2.8 to 3.8 AMeV with a large increase of bombarding energy, 32 to 50 AMeV. (authors)

[en] The wave packet shrinking effect, as well as the diffusion effect, is introduced into the quantum branching process of the antisymmetrized molecular dynamics through the memory effect in the fluctuation, so that the single particle dynamics can reproduce the prediction by the mean field models more precisely than before. The shrinking effect is expected to change the diffusion property of nucleons in nuclear matter. The central ¹²⁹Xe + Sn collisions at 50 MeV/u are calculated by the old and new methods, and it is shown that the new method for the wave packet shrinking has a large effect on the multifragmentation in a big expanding system with a moderate expansion velocity. (author)

[en] Isospin transport within a nuclear system is influenced by the density dependence of the symmetry energy. Studying isospin transport over relatively long times can therefore be a powerful tool to learn about the symmetry energy. The transiently deformed PLF^* formed in an intermediate energy heavy-ion collision presents an opportunity to study isospin transport for a variety of initial configurations. Isospin transport is found to persist over several hundred fm/c, establishing the timescale for isospin equilibration. (orig.)

[en] Antisymmetrized molecular dynamics with quantum branching is generalized so as to allow finite time duration of the unrestricted coherent mean field propagation, which is followed by the decoherence into wave packets. In this new model, the wave packet shrinking by the mean field propagation is respected as well as the diffusion, so that it predicts a one-body dynamics similar to that in mean field models. The shrinking effect is expected to change the diffusion property of nucleons in nuclear matter and the global one-body dynamics. The central ¹²⁹Xe+Sn collisions at 50 MeV/nucleon are calculated by the models with and without shrinking, and it is shown that the inclusion of the wave packet shrinking has a large effect on the multifragmentation in a big expanding system with a moderate expansion velocity

[en] Anti-symmetrized molecular dynamics with quantum branching is generalized so as to allow finite time duration of the unrestricted coherent mean field propagation which is followed by the decoherence into wave packets. In this new model, the wave packet shrinking by the mean field propagation is respected as well as the diffusion, so that it predicts a one-body dynamics similar to that in mean field models. The shrinking effect is expected to change the diffusion property of nucleons in nuclear matter and the global one-body dynamics. The central ¹²⁹Xe + Sn collisions at 50 MeV/nucleon are calculated by the models with and without shrinking, and it is shown that the inclusion of the wave packet shrinking has a large effect on the multifragmentation in a big expanding system with a moderate expansion velocity. (author)

[en] Noncentral collisions of ¹¹⁴Cd projectiles with ⁹²Mo target nuclei at E/A=50 MeV are explored with an antisymmetrized molecular dynamics model. These collisions are found to be essentially binary in character with formation of an excited projectile-like fragment (PLF*) and targetlike fragment (TLF*). The average excitation energy deduced for the PLF* and TLF* saturates for midcentral collisions, 3.5≤b≤6 fm, with its magnitude depending on the cluster recognition time. For short cluster recognition times (t=150 fm/c), an average excitation energy as high as ≅6 MeV is determined, indicating a short statistical lifetime for the fragments produced. Evidence for such a rapid deexcitation is observed in the present calculations

[en] A method for achieving good position resolution of low-intensity electron signals using a microchannel plate resistive anode detector is demonstrated. Electron events at a rate of 7 counts s"−"1 are detected using a Z-stack microchannel plate. The dependence of position resolution on both the distance and the potential difference between the microchannel plate and resistive anode is investigated. Using standard commercial electronics, a measured position resolution of 170 μm (FWHM) is obtained, which corresponds to an intrinsic resolution of 157 μm (FWHM)

[en] Invariant transverse-velocity spectra of intermediate-mass fragments were measured with the 4π multi-detector system INDRA for collisions of ¹⁹⁷Au on ¹⁹⁷Au at incident energies between 40 and 150 MeV per nucleon. Their scaling properties as a function of incident energy and atomic number Z are used to distinguish and characterize the emissions in (i) peripheral collisions at the projectile and target rapidities, and in (ii) central and (iii) peripheral collisions near mid-rapidity. The importance of dynamical effects is evident in all three cases and their origin is discussed. (orig.)