A Diffusion Equation from the Relativistic Ornstein–Uhlenbeck Process

We derive, in the hydrodynamic limit (large space and time scales), an evolution equation for the particle density in physical space from the (special) relativistic Ornstein–Uhlenbeck process introduced by Debbasch, Mallick, and Rivet. This equation turns out to be identical with the classical diffusion equation, without any relativistic correction. We prove that, in the hydrodynamic limit, this result is indeed compatible with special relativity.     

Nuclear multifragmentation and phase transition for hot nuclei

This review article is focused on the tremendous progress realized during the last fifteen years in the understanding of multifragmentation and its relationship to the liquid-gas phase diagram of nuclei and nuclear matter. The explosion of the whole nucleus, early predicted by Bohr [N. Bohr, Nature 137 (1936) 351], is a very complex and rich subject which continues to fascinate nuclear physicists as well as theoreticians who extend the thermodynamics of phase transitions to finite systems.     

Excitation energy partition in deeply inelastic collisions between40Ar and Ag at 27 MeV per nucleon

The dynamics of the two partners produced in dissipative collisions has been experimentally studied for the system⁴⁰Ar + Ag at 27 MeV per nucleon. Primary masses of the fragments can then be calculated; the excitation energy partition between the two fragments is derived from the number of particles evaporated by each fragment. We found that this division evolves from equipartition to a repartition close to thermal equilibrium in the excitation energy range 300–350 MeV or interaction times 5-10×l0^?22 s.     

Deeply inelastic transfer reactions induced by heavy ions in rare-earth targets

Recoil techniques have been used for a systematic study of deeply inelastic transfer reactions induced in rare earth targets by⁴⁰Ar,⁵²Cr,⁵⁶Fe and⁶³Cu projectiles. The targets were separated isotopes of Eu, Sm, Nd and Pr. The residual nuclei^149gTb,¹⁵⁰Dy and¹⁵¹Dy were identified by their radioactive properties. The reactions studied involved the transfer of 3 to 7 charges from projectile to target. The c.m. angular and energy distributions were measured over the whole angular range from 0 to 180° (c.m.). A special device was used to measure accurately the c.m. energy of products emitted in the angular range 170–180° in the c.m.s. The c.m. angular distributions depend strongly on the ratio of the incident energy to the strong interaction barrier, and slightly on the number of transferred charges. The c.m. energy distributions are typical of completely damped collisions for 6-charge transfer reactions, and include a contribution of partially damped collisions for 4-charge transfer reactions. A kinematic analysis was used to determine the most probable number of neutrons transferred in the first reaction step with a given number of protons. The numbers found correspond to equilibration of the neutron to proton ratio in the composite system.     

Break-up stage restoration in multifragmentation reactions

In the case of Xe + Sn at 32MeV/nucleon multifragmentation reaction break-up fragments are built up from the experimentally detected ones using evaluations of light-particle evaporation multiplicities which thus settle fragment internal excitation. Freeze-out characteristics are extracted from experimental kinetic energy spectra under the assumption of full decoupling between fragment formation and energy dissipated in different degrees of freedom. The thermal kinetic energy is determined uniquely while for the freeze-out volume - collective energy a multiple solution is obtained. The coherence between the solutions of the break-up restoration algorithm and the predictions of a multifragmentation model with identical definition of primary fragments is regarded as a way to select the true value. The broad kinetic energy spectrum of ³He is consistent with the break-up genesis of this isotope.     

Energy measurement and fragment identification using digital signals from partially depleted Si detectors

In this work we devise a new method to study quark-anti-quark interactions beyond simple ladder-exchange that yield massless pions in the chiral limit. The method is based on the requirement to have a representation of the quark-gluon vertex that is explicitly given in terms of quark dressings functions. We outline a general procedure to generate the Bethe-Salpeter kernel for a given vertex representation. Our method allows not only the identification of the mesons' masses but also the extraction of their Bethe-Salpeter wave functions exposing their internal structure. We exemplify our method with vertex models that are of phenomenological interest.     

Thermal and chemical equilibrium for vaporizing sources

Vaporized sources produced in collisions between ³⁶Ar and ⁵⁸Ni at 95 MeV per nucleon have been detected with the multidetector INDRA. Complete information concerning the deexcitation properties of quasi-projectiles, including second moments of chemical composition, is compared to a quantum statistical model describing a gas of fermions and bosons in thermal and chemical equilibrium. Inclusions in the calculation of all known discrete levels of nuclear species which deexcite into light particles and of a final state excluded volume interaction are found decisive to very well reproduce the experimental data, which strongly supports that thermodynamical equilibrium was achieved at freeze-out for such sources. Received: 6 April 1999