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Register a new userNegative heat capacity for hot nuclei using formulation from the microcanonical ensemble INDRA Collaboration
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By using freeze-out properties of multifragmenting hot nuclei produced in quasifusion central $^{129}$Xe+$^{nat}$Sn collisions at different beam energies (32, 39, 45 and 50 AMeV) which were estimated by means of a simulation based on experimental data collected by the $4pi$ INDRA multidetector, heat capacity in the thermal excitation energy range 4 - 12.5 AMeV was calculated from total kinetic energies and multiplicities at freeze-out. The microcanonical formulation was employed. Negative heat capacity which signs a first order phase transition for finite systems is observed and confirms previous results using a different method.
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A global protocol for the thermostatistical analysis of hot nuclear sources is discussed. Within our method of minimization of variances we show that the abnormal kinetic energy fluctuation signal recently reported in different experimental data (M.DAgostino et al.-Phys. Lett. B 473 (2000) 219, N. Le Neindre et al.- contr. to the XXXVIII Bormio Winter Meeting on Nucl. Phys. (2001) 404) is a genuine signal of a first order phase transition in a finite system.
We derive the microcanonical partition function of the ideal relativistic quantum gas of spinless bosons in a quantum field framework as an expansion over fixed multiplicities. Our calculation generalizes well known expressions in literature in that it does not introduce any large volume approximation and it is valid at any volume. We discuss the issues concerned with the definition of the microcanonical ensemble for a free quantum field at volumes comparable with the Compton wavelength and provide a consistent prescription of calculating the microcanonical partition function, which is finite at finite volume and yielding the correct thermodynamic limit. Besides an immaterial overall factor, the obtained expression turns out to be the same as in the non-relativistic multi-particle approach. This work is introductory to derive the most general expression of the microcanonical partition function fixing the maximal set of observables of the Poincare group.
We derive the microcanonical partition function of the ideal relativistic quantum gas with fixed intrinsic angular momentum as an expansion over fixed multiplicities. We developed a group theoretical approach by generalizing known projection techniques to the Poincare group. Our calculation is carried out in a quantum field framework and applies to particles with any spin. It extends known results in literature in that it does not introduce any large volume approximation and it takes particle spin fully into account. We provide expressions of the microcanonical partition function at fixed multiplicities in the limiting classical case of large volumes and large angular momenta and in the grand-canonical ensemble. We also derive the microcanonical partition function of the ideal relativistic quantum gas with fixed parity.
This review article takes stock of the progress made in understanding the phase transition in hot nuclei and highlights the coherence of observed signatures
The empirical heat capacities of $^{93-98}$Mo nuclei are re-investigated by using the latest updated and recommended nuclear level density (NLD) data below the neutron binding energy $B_n$ combined with the back-shifted Fermi-gas (BSFG) model for the energy region above $B_n$. For the latter, the BSFG formula with energy-dependent level density parameter is used and the new parameterization has been carried out in order to obtain the best fit to the new NLD data in the whole data range. The results obtained show that the S-shaped heat capacity, a fingerprint of the pairing phase transition, is more pronounced in even $^{94,96,98}$Mo nuclei than that in odd $^{93,95,97}$Mo isotopes. This result is different with those obtained in two previous studies by R. Chankova et al., [Phys. Rev. C {bf 73}, 034311 (2006)] and K. Kaneko et al., [Phys. Rev. C {bf 74}, 024325 (2006)], in which the old NLD data and the BSFG model with energy-independent level density parameter were used. Moreover, the present work suggests that the very strong S-shape observed in the heat capacities of both even and odd Molybdenum isotopes by K. Kaneko et al., [Phys. Rev. C {bf 74}, 024325 (2006)] should be re-investigated. The present work also suggests that obtain the correct heat capacity and associated pairing phase transition in excited nuclei, one should use the correct NLD data and the best fitted BSFG NLD in the entire region where the experimental data are available.
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