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  • 25.70.Np  (4)
  • 21.60−n  (1)
  • 25.70. Jj  (1)
Materialart
Erscheinungszeitraum
Schlagwörter
  • 1
    Digitale Medien
    Digitale Medien
    Springer
    The European physical journal 337 (1990), S. 81-95 
    ISSN: 1434-601X
    Schlagwort(e): 25.70.-Z ; 25.70.Np
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We have used scaling properties of nuclear multifragmentation, which have been observed with emulsion data, to investigate the properties of some approaches based on percolation. We have studied different percolation models on a cubic lattice and shown that they can rather well reproduce the data except for binary break up. We have described what the mean field approximation would give in this context and showed that it cannot reproduce the experimental results. Most of the paper is focused on the restructured aggregation model introduced earlier which allows to well reproduce the scaling properties observed experimentally. This model has been studied in details and extended to take account of bonds breaking. It is shown that, in some cases, a nucleus can break up in two pieces. This process cannot be obtained in conventional percolation or aggregation but is observed experimentally in the emulsion data. Other features like the dimensionality of the aggregation model, the restructuration of the clusters and a schematic constraint in momentum space have also been investigated.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    ISSN: 1434-601X
    Schlagwort(e): 25.40.Sc ; 25.70.Np
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We have studied the fragmentation of Au projectiles interacting with targets of C, Al and Cu at an incident energy ofE/A=600 MeV. The employed inverse kinematics allowed a nearly complete detection of projectile fragments with chargeZ≧2. The recorded fragmentation events were sorted according to three observables, the multiplicityM lp of light charged particles, the largest atomic numberZ max within an event, and a new observable,Z bound, representing the sum of the atomic numbersZ of all fragments withZ≧2. Using these observables, the impact parameter dependence of the fragmentation process was investigated. For all three targets, a maximum mean multiplicity of 3 to 4 intermediate mass fragments (IMFs) is observed. The corresponding impact parameters range from central collisions for theC target to increasingly peripheral collisions for the heavier targets. It is found that the correlation between the IMF multiplicity andZ bound, extending from evaporation type processes (largeZ bound) to the total disassembly of the projectile (smallZ bound), is independent of the target nucleus. This universal behaviour may suggest an — at least partial — equilibration of the projectile fragment prior to its decay.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    The European physical journal 325 (1986), S. 347-355 
    ISSN: 1434-601X
    Schlagwort(e): 25.70.−Z ; 25.70.Np ; 25.70.Gh ; 25.70.Jj ; 05.90+m
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We have used a spherical time dependent Thomas Fermi model to study the expansion of hot and/or compressed nuclei. This approach was coupled to a site-bond percolation model to study the disassembly of the nucleus into many pieces (multifragmentation). We find that a non compressed nucleus undergoes multifragmentation if the thermal excitation energy is larger than 70% of its binding energy. If the nucleus is compressed this value is notably decreased.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    Springer
    The European physical journal 323 (1986), S. 419-435 
    ISSN: 1434-601X
    Schlagwort(e): 21.60−n ; 25.70 Gh ; 27.80+W
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract A hydrodynamical approach and the Thomas Fermi approximation have been used to study the evolution of hot and compressed nuclei. Spherical symmetry was assumed in the calculation. The dynamical equations have been transformed into “Schrödinger like” equations (using the Madelung transformation) and were solved numerically. Dissipation was simulated in the same way as in the Navier-Stokes equation by introducing shear and bulk viscosities. Global as well as local thermal equilibrium have been studied. The model has been applied to small amplitude oscillations (the breathing mode) and to the stability of hot and compressed nuclei. It was found that compression is more efficient to break nuclei than thermal excitation. The relaxation time for global equilibrium was estimated to be of the order of 10−22 s. It was found that the results obtained in the case of global and local thermal equilibrium are very similar.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    Springer
    The European physical journal 322 (1985), S. 419-426 
    ISSN: 1434-601X
    Schlagwort(e): 25.70. Jj
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We have developed a very schematic static model to calculate the most probable amount of linear momentum transfer, $$\tilde \rho$$ , that a projectile can transmit to a fusing system in heavy ion collisions at bombarding energies between ∼10 and 20 MeV/u. This approach estimates the conditions necessary in phase space for nucleons to be emitted by the mean field of one of the two nuclei. Due to its simplicity this model gives a qualitative description of the data and it is only expected to provide some general numerical trends of $$\tilde \rho$$ as a function of the macroscopic parameters of the reaction. It is found that $$\tilde \rho$$ depends not only on the bombarding energy per nucleon but also on the masses of the projectiles and targets. Finally, the question of the amount of maximum energy that a nucleus can sustain under the condition of global statistical equilibrium is investigated. It is found that the mass asymmetry of the system is an all important parameter in determining the limits of fusion related to this maximum excitation energy content.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    Springer
    The European physical journal 328 (1987), S. 101-113 
    ISSN: 1434-601X
    Schlagwort(e): 25.70-z ; 25.70.Np ; 25.70.Gh ; 25.70.Jj ; 05.90.+m
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We present a simple model to describe the evolution of hot and compressed nuclei. It is based on irrotational hydrodynamics and a 3-dimensional site-bond percolation model. Hydrodynamics is used if the evolution of the system is dominated by the mean field. This situation occurs when the fluctuations of the mean field are small. These latter are evaluated using the percolation model. In some cases it turns out that these fluctuations become very large and the system breaks up into several pieces (multifragmentation). The results of this process are described by the percolation model. We have obtained analytical or fitted expressions for all the results which compare well with those obtained in a previous and more involved model based on the same physical ideas. In particular we found that a noncompressed nucleus undergoes multifragmentation if the thermal excitation energy is larger than 70% of its binding energy. If the nucleus is compressed this value is notably decreased.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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