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Register a new userCaloric curve for finite nuclei in relativistic models
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In this work we calculate the caloric curve (excitation energy per particle as a function of temperature) for finite nuclei within the non--linear Walecka model for different proton fractions. It is shown that the caloric curve is sensitive to the proton fraction. Freeze-out volume effects in the caloric curve are also studied.
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Isotopic effects in projectile fragmentation at relativistic energies have been studied with the ALADIN forward spectrometer at 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. Chemical freeze-out temperatures are found to be nearly invariant with respect to the A/Z ratio of the produced spectator sources, consistent with predictions for expanded systems. Consequences for the proposed interpretation of chemical breakup temperatures as representing the limiting temperatures predicted by microscopic models are discussed.
New Relativistic mean field parameter set IOPB-I has been developed.
Caloric curves have traditionally been derived within the microcanonical ensemble via dS/dE=1/T or within the canonical ensemble via E=T^2*d(ln Z)/dT. In the thermodynamical limit, i.e., for large systems, both caloric curves give the same result. For small systems like nuclei, the two caloric curves are in general different from each other and neither one is reasonable. Using dS/dE=1/T, spurious structures like negative temperatures and negative heat capacities can occur and have indeed been discussed in the literature. Using E=T^2*d(ln Z)/dT a very featureless caloric curve is obtained which generally smoothes too much over structural changes in the system. A new approach for caloric curves based on the two-dimensional probability distribution P(E,T) will be discussed.
The A/Z dependence of projectile fragmentation at relativistic energies has been studied with the ALADIN forward spectrometer at SIS. A stable beam of 124Sn and radioactive beams of 124La and 107Sn at 600 MeV per nucleon have been used in order to explore a wide range of isotopic compositions. Chemical freeze-out temperatures are found to be nearly invariant with respect to the A/Z of the produced spectator sources, consistent with predictions for expanded systems. Small Coulomb effects (Delta T approx 0.6 MeV) appear for residue production near the onset of multifragmentation.
We analyze the localization properties of two-body correlations induced by pairing in the framework of relativistic mean field (RMF) models. The spatial properties of two-body correlations are studied for the pairing tensor in coordinate space and for the Cooper pair wave function. The calculations are performed both with Relativistic-Hatree-Bogoliubov (RHB) and RMF+Projected-BCS (PBCS) models and taking as examples the nuclei $^{66}$Ni, $^{124}$Sn and $^{200}$Pb. It is shown that the coherence length have the same pattern as in previous non-relativistic HFB calculations, i.e., it is maximum in the interior of the nucleus and drops to a minimum in the surface region. In the framework of RMF+PBCS we have also analysed, for the particular case of $^{120}$Sn, the dependence of the coherence length on the intensity of the pairing force. This analysis indicates that pairing is reducing the coherence length by about 25-30 $%$ compared to the RMF limit.
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