International Journal of Modern Physics E

We review current ideas on entropy production during the different stages of a relativistic nuclear collision. This includes recent results on decoherence entropy and the entropy produced during the hydrodynamic phase by viscous effects. We start by a discussion of decoherence caused by gluon bremsstrahlung in the very first interactions of gluons from the colliding nuclei. We then present a general framework, based on the Husimi distribution function, for the calculation of entropy growth in quantum field theories, which is applicable to the early ("glasma") phase of the collision during which most of the entropy is generated. The entropy calculated from the Husimi distribution exhibits linear growth when the quantum field contains unstable modes and the growth rate is asymptotically equal to the Kolmogorov–Sinaï entropy. We outline how the approach can be used to investigate the problem of entropy production in a relativistic heavy ion reaction from first principles. We show that the same result can be obtained in the framework of a completely different approach called eigenstate thermalization hypothesis. Finally we discuss some recent results on entropy production in the strong coupling limit, as obtained from AdS/CFT duality.

An attempt is made to study multifractal specific heat from F_q, modified G_q and Takagi moments, which can provide some interesting information about event-by-event fluctuations in heavy-ion collisions at high energies. It is an established fact that constancy of the specific heat (CSH) of solids and gases helps explain thermodynamical behavior of intermittency and multifractality in A–A collisions at different projectile energies. It is worthmentioning that the present paper deals with multifractal specific heat, c, extracted from F_q, modified G_q and Takagi moments for the experimental as well as FRITIOF generated data on 14.5A GeV/c²⁸Si-nucleus interactions. The results obtained using the three approaches are compared for both the data sets. The observed power law behavior reflects self-similar property of the multiparticle production process. The common feature of the multifractal specific heat obtained using the three approaches is that there is no systematic variation in its value for different orders of the moments. Furthermore, the value of c is found to be different for both the data sets and no strong target mass dependence is observed in any of the cases. A noteworthy observation is that a non-zero finite value of the multifractal specific heat may be considered a good signal for the presence of multifractality in the relativistic charged particle multiplicity distribution.

The ground state properties namely the binding energy, the root mean square (rms) radius (neutron, proton and charge) and the deformation parameter of 45 newly identified neutron-rich isotopes in the A~71–152 mass region have been predicted in the relativistic mean filed (RMF) framework along with the Bardeen–Cooper–Schrieffer (BCS) type of pairing. Validity of the RMF results with the NL3 effective force are tested for odd-A Zn and Rh isotopic chains without taking the time reversal symmetry breaking effects into consideration. The RMF prediction on the binding energies are in good agreement with the empirical/finite-range droplet model calculation. The shell effects on the rms radii of odd-A Zn and Rh isotopes are nicely reproduced. The possibility of shape-coexistence in the newly identified nuclei is discussed.

Formation cross-sections of evaporation residues have been measured in ¹⁹F+¹⁵⁹Tb reaction at E_lab=83, 88, 93, 98 and 103 MeV using recoil catcher technique followed by off-line gamma-ray spectrometry. Significant contribution from incomplete fusion has been observed at these low beam energies indicating the contribution to incomplete fusion from collision trajectories with angular momentum (l) less than the critical angular momentum for complete fusion (l_cr(CF)). Incomplete fusion cross-sections could be explained using a modified sum-rule model which allows effective competition from incomplete fusion for collision trajectories with l<l_cr(CF).

In the present work we describe our results concerning the calculation of equation of state of symmetric zero temperature nuclear matter and the microscopic optical potential using the soft-core Argonne inter-nucleon potentials in first order Brueckner–Hartree–Fock (BHF) theory. The nuclear matter saturates at a density 0.228 nucleon/fm³ with 17.52 MeV binding energy per nucleon for Argonne av-14 and at 0.228 nucleon/fm³ with 17.01 MeV binding energy per nucleon for Argonne av-18. As a test case we present an analysis of 65 and 200 MeV protons scattering from ²⁰⁸Pb. The Argonne av-14 has been used for the first time to calculate nucleon optical potential in BHF and analyze the nucleon scattering data. We also compare our reaction matrix results with those using the old hard-core Hamada–Johnston and the soft-core Urbana uv-14 and Argonne av-18 inter-nucleon potentials. Our results indicate that the microscopic potential obtained using av-14 gives marginally better agreement with the experimental data than the other three Hamiltonians used in the present work.

Isomeric state excitation in the ¹²⁰Te(γ,n)^119m,gTe reaction within the 10–20 MeV energy range has been studied with bremsstrahlung beams. Energy dependences of experimental isomeric yields ratios and reaction cross-sections have been obtained. Experimental results are compared with TALYS-1.2 calculations.

In this work we have discussed dependence of surface tension coefficient that appears in proximity potential and energy of incident nucleus. The obtained results from study of the fusion barrier heights and positions for 44 reactions with z≥8 reveal that this modification on the formalism of proximity model leads to a better agreement between computed fusion barrier heights and positions and experimental data.

The high-spin states of ¹⁰⁸Ag have been studied by the in-beam γ spectroscopy with the reaction ¹⁰⁴Ru(⁷Li,3n)¹⁰⁸Ag at a beam energy of 33 MeV. The previously known positive-parity band structures have been extended up to higher spins. Their configurations are discussed based on alignments, band-crossing frequencies, and B(M1)/B(E2) ratios.

Photofission cross-section of ²³⁸U was measured using bremsstrahlung radiation energy 7.4–9.0 MeV with energy step of 0.4 MeV by employing Lexan polycarbonate film as solid state nuclear track detector (SSNTD). The photon intensity from the Microtron accelerator at a distance of 15 cm from the bremsstrahlung converter (tantalum target) facility was estimated to be 10¹⁰ photons/sec using the code EGS-4. In this paper, details of the fission fragment angular distribution measurements of ²³⁸U target using Lexan polycarbonate have been discussed. The photofission cross-section was calculated using the angular distribution of fission fragments and the results were compared with those obtained using the code EMPIRE-II and various barrier parameters of the RIPL-1, RIPL-2 libraries and with the new analytical fission barrier formula based on the Hugenholtz–Van Hove theorem. The present experimental measurements were in good agreement with the results obtained from the Empire-II code predictions for potential parameter taken from RIPL-1 and a newly developed analytical fission barrier formula.

The model of transitions in the medium based on field-theoretical approach is considered. The time-dependence and corrections to the model are studied. The lower limit on the free-space oscillation time τ is in the range 10¹⁶yr>τ>1.2×10⁹s.

Based on the observation of the long-lived isotopes of roentgenium, ²⁶¹Rg and ²⁶⁵Rg(Z = 111, t_1/2≥10⁸y) in natural Au, an experiment was performed to enrich Rg in 99.999% Au. 16 mg of Au were heated in vacuum for two weeks at a temperature of 1127°C(63°C above the melting point of Au). The content of ¹⁹⁷Au and ²⁶¹Rg in the residue was studied with high resolution inductively coupled plasma-sector field mass spectrometry (ICP-SFMS). The residue of Au was 3×10^-6 of its original quantity. The recovery of Rg was a few percent. The abundance of Rg compared to Au in the enriched solution was about 2×10^-6, which is a three to four orders of magnitude enrichment. It is concluded that the evaporation rate of Rg from an Au matrix in vacuum at 63°C above the Au melting point is lower than that of Au. This experiment reinforces our first observation of Rg in a terrestrial material. As before it is concluded that a long-lived isomeric state exists in ²⁶¹Rg and that it probably belongs to a new class of isomeric states, namely high spin (K-type) super- or hyperdeformed isomeric states.

Negative results obtained in AMS searches by Dellinger et al. on mostly unrefined ores have led them to conclude that the very heavy long-lived species found in chemically processed samples with ICP-SFMS by Marinov et al. are artifacts. We argue that it may not be surprising that results obtained from small random samplings of inhomogeneous natural minerals would contrast with concentrations found in homogeneous materials extracted from large quantities of ore. We also point out that it is possible that the groups of counts at masses 296 and 294 seen by Dellinger et al. could be, within experimental uncertainties, due to ²⁹⁶Rg and ²⁹⁴eka-Bi in long-lived isomeric states. In such case, the experiments of Dellinger et al. lend support to the experiments of Marinov et al.