Multifragmentation - what the data tell us about the different models

We discuss what the presently collected data tell us about the mechanism of multifragmentation by comparing the results of two different models, which assume or show an opposite reaction scenario, with the recent high statistics $4\pi$ experiments performed by the INDRA collaboration. We find that the statistical multifragmentation model and the dynamical Quantum Molecular Dynamics approach produce almost the same results and agree both quite well with experiment. We discuss which observables may serve to overcome this deadlock on the quest for the reaction mechanism. Finally we proof that even if the system is in equilibrium, the fluctuation of the temperature due to the smallness of the system renders the caloric curve useless for the proof of a first order phase transition.Comment: Proceedings CRIS 200

Thermodynamics - a valuable approach to multifragmentation?

Since years it has been vividly debated whether multifragmentation is a thermal or a dynamical process. Recently it has been claimed \cite{toek1,po} that new data allow to decide this question. The conclusion, drawn in these papers, are, however, opposite. Whereas \cite{toek1} states that the behavior of different observables as a function of the fragment multiplicity excludes a thermal origin of the fragments in \cite{po} it has been argued that data show a first order phase transition between a liquid and a gaseous phase. It is the aim of this paper to show that both conclusions are premature. They are based on the salient assumption, that the system is sufficiently large to be susceptible to a canonical description. We will show that this is not the case. A micro canonical approach describes the data as good as dynamical calculations. Hence the quest for the physical origin of multifragmentation continues.Comment: 17 pages, 4 figures, completely revised, accepted for publication in NP

Dynamical fragment production in central collisions Xe(50 A.MeV)+Sn

For central collisions Xe(50 A.MeV)+Sn we compared experimental data from the INDRA detector with QMD simulations. Theory as well as experiment show a clear binary character of the fragment emission even for very central collisions. From the time evolution of the reaction (QMD simulation) we could built up a scenario for the dynamical emission of fragmentsComment: To appear in the Proceedings of the 36th International Winter Meeting on Nuclear Physics, Bormio, Italy, Jan. 26-31 199

On the origin of the radial flow in low energy heavy ion reactions

The average transverse energy of nucleons and intermediate mass fragments observed in the heavy ion reaction Xe(50A MeV)+Sn shows the same linear increase as a function of their mass as observed in heavy ion collisions up to the highest ene rgies available today and fits well into the systematics. At higher energies this observation has been interpreted as a sign of a strong radial flow in an otherwise thermalized system. Investigating the reaction with Quantum Molecular dynamics simulations we find in between 50A MeV and 200A MeV a change in the reaction mechanism. At 50A MeV the apparent radial flow is merely caused by an in-plane flow and Coulomb repulsion. The average transverse fragment energy does not change in the course of the reaction and is equal to the initial fragment energy due to the Fermi motion. At 200A MeV, there are two kinds of fragments: those formed from spectator matte r and those from the center of the reaction. There the transverse energy is caused by the pr essure from the compressed nuclear matter. In both cases we observe a binary event stru cture, even in central collisions. This demonstrates as well the non thermal character of the reaction. The actual process which leads to multifragmentation is rather complex and is discussed in detail.Comment: 12 pages, 9 figures, revised version (submitted to NPA

Role of the experimental filter in obtaining the Arrhenius plot in multifragmentation reactions

Recently it has been argued that the linear relation between the transverse energy and the apparent probability to emit a fragment proves that the total system is in thermal equilibrium. It is shown, for a specific reaction Xe+Sn at 50 A.MeV, that the same behavior is obtained in the context of Quantum Molecular Dynamical without invoking the idea of equilibrium. The linear dependance is shown to be a detector effect.Comment: 11 pages, 4 Postscript figures. Submitted Phys. Rev. Let

Microscopic approach to the spectator matter fragmentation from 400 to 1000 AMeV

A study of multifragmentation of gold nuclei is reported at incident energies of 400, 600 and 1000 MeV/nucleon using microscopic theory. The present calculations are done within the framework of quantum molecular dynamics (QMD) model. The clusterization is performed with advanced sophisticated algorithm namely \emph{simulated annealing clusterization algorithm} (SACA) along with conventional spatial correlation method. A quantitative comparison of mean multiplicity of intermediate mass fragments with experimental findings of ALADiN group gives excellent agreement showing the ability of SACA method to reproduce the fragment yields. It also emphasizes the importance of clustering criterion in describing the fragmentation process within semi-classical model

Concept For Automated Economic Evaluation Of AI Applications In The Production

An unclear economic benefit is one of the biggest obstacles for companies to use AI applications in their production. Various methods exist for deriving the economic efficiency of AI applications in a company's own production, but these have to be considered individually for each use case. In addition, they rely on the statements of the software manufacturers with regard to efficiency gains, quality gains, and other KPIs. In the course of the FabOS research project, a concept was developed that uses Asset Administration Shells and ML clustering for the automated economic evaluation of AI applications in the production

Transverse flow of nuclear matter in collisions of heavy nuclei at intermediate energies

The Quantum Molecular Dynamics Model (IQMD) is used to investigate the origin of the collective transverse velocity observed in heavy ion experiments. We find that there are three contributions to this effect: initial-final state correlations, potential interactions and collisions. For a given nuclear equation of state (eos) the increase of the transverse velocity with increasing beam energy is caused by the potential part. For a given beam energy the collective transverse velocity is independent of the nuclear eos but the relative contributions of potential and collisions differ. In view of the importance of the potential interactions between the nucleons it is not evident that the similarity of the radial velocities measured for fragments at beam energies below 1 AGeV and that for mesons at beam energies above 2 AGeV is more than accidental.Comment: 5 pages, 5 figures, revtex, OASIS ref PLB1700