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The effect of entrance channel on the relative strength of pre-equilibrium emission, basic pre-equilibrium parameters, excitation functions for proton and alpha induced reactions on 64Ni have been analyzed over the energy range from threshold up to 40 MeV. The results have been compared with the theoretical cross-sections calculated by means of the code EMPIRE3.2.3-MALTA and TALYS 1.6. [ABSTRACT FROM AUTHOR]

Study of the mechanism of pre-equilibrium particle emission in alpha particle induced reactions has been done in the present work. The cross-sections for systems α + 144Sm and α + 154Sm have been calculated using the statistical model code ALICE-91. Significant pre-equilibrium particle emission contribution has been obtained for these systems at higher projectile energy. At higher projectile energies, the pre-equilibrium particle emission has been found to affect predominantly over the equilibrated compound nucleus emissions. The contribution of pre-equilibrium particle emission is found larger for α + 144Sm system than that of α + 154Sm system. The present results indicate that the systems having spherical targets have more contribution of pre-equilibrium particle emission than that of systems with deformed targets. These results suggest that the shape of target (spherical or deformed) also affect the dynamics of pre-equilibrium particle emission at energy above the fusion barrier. [ABSTRACT FROM AUTHOR]

To understand the mechanism of pre-equilibrium particle emission using light and heavy ion beams with different targets at energy above the Coulomb barrier, a study has been done. The cross-sections for twelve systems 4He + 59Co, 4He +124Sn, 4He + 165Ho, 12C + 59Co, 12C +124Sn, 12C + 165Ho, 16O + 59Co, 16O + 124Sn, 16O + 165Ho, 19F + 59Co, 19F + 124Sn and 19F + 165Ho have been calculated using the statistical model code ALICE-91. Significant pre-equilibrium particle emission contribution has been obtained for lighter systems at higher projectile energy. It has also been found that the pre-equilibrium particle emission affects predominantly over the equilibrated compound nucleus emissions at high projectile energies. Pre-equilibrium fraction (FPEQ) has been deduced from the excitation function data for different systems at different projectile energies. The present results indicate that the probability of pre-equilibrium particle emission depends not only on a single entrance channel parameter, but it also depends on various entrance channel parameters, namely: projectile energy, mass of the projectile, mass of the target and entrance-channel mass asymmetry. The present analysis of the data also suggests that the pre-equilibrium particle emission contributes significantly at higher projectile energy for lighter mass projectile and target. [ABSTRACT FROM AUTHOR]

Abstract The excitation functions of the proton induced A n a t g reactions were measured using the stack foil activation followed by the off-line γ -ray spectrometry. The present work was carried out at 14UD BARC-TIFR Pelletron accelerator, Mumbai, India. The proton beam of 22 MeV was used for the irradiation of the samples and was degraded along the stack of silver foils. The measured cross-section data were compared with the existing literature data available in EXFOR. The calculated excitation functions were also compared with the calculated values from TALYS-1.9 model code using a suitable input parameters for the pure compound nucleus (CN) and pre-equilibrium (PE) reaction cross-sections. ALICE-2014 code was also used to validate the present experimental findings as well as the TALYS-1.9 results. [ABSTRACT FROM AUTHOR]

We introduce and analyze an augmented mixed finite element method for the Navier–Stokes–Brinkman problem with nonsolenoidal velocity. We employ a technique previously applied to the stationary Navier–Stokes equation, which consists of the introduction of a modified pseudostress tensor relating the gradient of the velocity and the pressure with the convective term, and propose an augmented pseudostress–velocity formulation for the model problem. The resulting augmented scheme is then written equivalently as a fixed point equation, so that the well-known Banach fixed point theorem, combined with the Lax–Milgram lemma, are applied to prove the unique solvability of the continuous and discrete systems. We point out that no discrete inf–sup conditions are required for the solvability analysis, and hence, in particular for the Galerkin scheme, arbitrary finite element subspaces of the respective continuous spaces can be utilized. For instance, given an integer k ≥ 0 , the Raviart–Thomas spaces of order k and continuous piecewise polynomials of degree ≤ k + 1 constitute feasible choices of discrete spaces for the pseudostress and the velocity, respectively, yielding optimal convergence. We also emphasize that, since the Dirichlet boundary condition becomes a natural condition, the analysis for both the continuous an discrete problems can be derived without introducing any lifting of the velocity boundary datum. In addition, we derive a reliable and efficient residual-based a posteriori error estimator for the augmented mixed method. The proof of reliability makes use of a global inf–sup condition, a Helmholtz decomposition, and local approximation properties of the Clément interpolant and Raviart–Thomas operator. On the other hand, inverse inequalities, the localization technique based on element-bubble and edge-bubble functions, approximation properties of the L 2 -orthogonal projector, and known results from previous works, are the main tools for proving the efficiency of the estimator. Finally, some numerical results illustrating the performance of the augmented mixed method, confirming the theoretical rate of convergence and properties of the estimator, and showing the behavior of the associated adaptive algorithms, are reported. [ABSTRACT FROM AUTHOR]

We present a first principles approach to study the Chiral Magnetic Effect during the pre-equilibrium stage of a heavy-ion collision. We discuss the dynamics of the Chiral Magnetic Effect and Chiral Magnetic Wave based on real-time lattice simulations with dynamical (Wilson and Overlap) fermions simultaneously coupled to color and electromagnetic fields. While for light quarks we observe a dissipation-less transport of charges as in anomalous hydrodynamics, we demonstrate that for heavier quarks the effects of explicit chiral symmetry breaking lead to a significant reduction of the associated currents. [ABSTRACT FROM AUTHOR]

We calculate the yield of lepton pair production from jet-plasma interaction where the plasma is anisotropic in momentum space. We compare both the M and $ p_T$ distributions from such process with the Drell-Yan contribution. It is observed that the invariant mass distribution of the lepton pair from such process dominates over the Drell-Yan one up to 3GeV at RHIC and up to 10GeV at LHC. Moreover, it is found that the contribution from the anisotropic quark gluon plasma (AQGP) increases marginally compared to the isotropic QGP. In case of $p_{T}$ -distribution we observe an increase by a factor of 3-4 in the entire $p_{T}$ -range at RHIC for AQGP. However, at LHC the change in the p-distribution is marginal as compared to the isotropic case. It should be noted that we have used a two stage evolution scenario. First, the system evolves with pre-equilibrium state anisotropy up to $\tau_{iso}$ (the isotropization time). After that the system evolves hydrodynamically. [ABSTRACT FROM AUTHOR]

We discuss the importance of initial state and early time effects with regard to the theoretical understanding of long range azimuthal correlations observed in high-multiplicity p + p and p + A collisions. [ABSTRACT FROM AUTHOR]

For several years, various neutron evaluations of plutonium and uranium isotopes have been performed at Bruyères-le-Châtel (BRC), from 1 keV up to 30 MeV. Since only nuclear reaction models have been used to produce these evaluations, our approach was named the “Full Model” approach. Total, shape elastic and direct inelastic cross sections were obtained from the coupled channels model using a dispersive optical potential developed for actinides, with a large enough coupling scheme including the lowest octupolar band. All other cross sections were calculated using the Hauser-Feshbach theory (TALYS code) with a pre-equilibrium component above 8–10 MeV. In this paper, we focus our attention on the fission channel. More precisely, we will present the BRC contribution to fission modeling and the philosophy adopted in our “Full Model” approach. Performing evaluations with the “Full Model” approach implies the optimization of a large number of model parameters. With increasing neutron incident energy, many residual nuclei produced by nucleon emission also lead to fission. All available experimental data assigned to various fission mechanisms of the same nucleus were used to determine fission barrier parameters. For uranium isotopes, triple-humped fission barriers were required in order to reproduce accurately variations of the experimental fission cross sections. Our BRC fission modeling has shown that the effects of the class II or class III states located in the wells of the fission barrier sometimes provide an anti-resonant transmission rather than a resonant one. Consistent evaluations were produced for a large series of U and Pu isotopes. Resulting files were tested against integral data. [ABSTRACT FROM AUTHOR]

Background: The role of pre-equilibrium emission within the heavy-ion fusion process has not been fully characterized. An accurate description of this process is important for understanding the formation of the compound nucleus in fusion reactions. Purpose: We develop a systematic description, based on experimental measurements, of the strength of the pre-equilibrium process in heavy-ion fusion reactions. Method: With a view to study pre-equilibrium emission process, the excitation functions for some neutron emission channels occurring in the fusion of 12C with 128Te and 169Tm, and of 16O with 159Tb, 169Tm, and 181Ta, respectively, have been measured at incident energies from near the Coulomb barrier to ≈7 MeV/nucleon. The off-line γ-ray spectrometry-based activation technique has been used for the measurements of excitation functions. The measured excitation functions have been compared with theoretical predictions based on pure statistical model code pace4 and Geometry Dependent Hybrid (GDH)-based code alice-91. The strength of pre-equilibrium emission has also determined from comparison of the experimental excitation functions and the pace4 calculations. Results: The measured excitation functions are satisfactorily reproduced by the pace4 calculations in the energy region up to the peak position. However, at relatively higher energies, the enhancement of experimental cross sections in the tail portion of excitation functions as compared to the theoretical predictions of code pace4 has been observed. The observed deviation may be attributed to the pre-equilibrium emission of particles during the thermalization of the compound nucleus. Further, alice-91 calculations which include PE emission satisfactorily reproduce the experimental data even at higher energies, indicating the significant contribution of pre-equilibrium emissions. Conclusions: Analysis of data clearly indicates that pre-equilibrium emission is an important reaction mechanism even at low projectile energies where the compound nucleus reaction mechanism dominates, and pre-equilibrium fraction 'PFR strongly depends on excitation energy available for surface nucleons in composite systems above the Coulomb barrier and the mass of the composite system. [ABSTRACT FROM AUTHOR]

The article presents brief information on systematic study of neutron capture including the compound, pre-equilibrium, and direct mechanisms. Topics discussed include compound-nucleus capture reaction (CNC), pre-equilibrium capture reaction (PEC), and direct capture reaction, is discussed. Information on examination of astrophysical reaction rates, and nuclear-structure ingredients, is also offered.

Abstract: The ability to describe production of light fragments (LF) is important for many applications, such as cosmic-ray-induced single event upsets (SEUs), radiation protection, and cancer therapy with proton and heavy-ion beams. The cascade-exciton model (CEM) and the Los Alamos version of the quark-gluon string model (LAQGSM) event generators in the LANL transport code MCNP6, describe quite well the spectra of fragments with sizes up to 4He across a broad range of target masses and incident energies (up to ∼ 5 GeV for CEM and up to ∼ 1 TeV/A for LAQGSM). However, they do not predict the high-energy tails of LF spectra heavier than 4He well. Most LF with energies above several tens of MeV are emitted during the precompound stage of a reaction. The current versions of our event generators do not account for precompound emission of LF larger than 4He. The aim of our work is to generalize the precompound model to include such processes, leading to increased predictive power of LF production. Extending the model in this way provides preliminary results that have much better agreement with experimental data. [Copyright &y& Elsevier]

Abstract: A new approach is proposed for the calculation of non-equilibrium triton energy distributions in nuclear reactions induced by nucleons of intermediate energies. It combines models describing the nucleon pick-up, the coalescence and the triton knock-out processes. Emission and absorption rates for excited particles are represented by the pre-equilibrium hybrid model. The model of Sato, Iwamoto, Harada is used to describe the nucleon pick-up and the coalescence of nucleons from exciton configurations starting from (2p,1h) states. The contribution of the direct nucleon pick-up is described phenomenologically. Multiple pre-equilibrium emission of tritons is accounted for. The calculated triton energy distributions are compared with available experimental data. [Copyright &y& Elsevier]

Abstract: We discuss the general concept of exclusive emission cross sections and spectra and the exclusive spectra of the ENDF library. We briefly review the exclusive hybrid Monte Carlo simulation model and show how its exclusive cross sections can be integrated into the reaction code EMPIRE-3.1. We close by discussing several examples. [Copyright &y& Elsevier]

Abstract: We address the angular momentum effects within the state density approach to the Iwamoto-Harada-(Bisplinghoff) model of the pre-equilibrium cluster emission. Using this way, the cluster emission is independent of the cluster formation probability, which — using a rough approximation — contains also all angular momenta couplings related to the creation of a cluster in nuclear reaction. Consequently, the angular-momentum part of the cluster emission rate is formally the same as it is in the nucleon emission case (but energy parts are substantially different). The 197Au(p,α) reaction at 62 MeV serves as an illustration of the suggested model. Inclusion of spin variables causes the enhancement of the α channel (and a weakening of the sum of nucleon channels due to particle emission competition) compared to the spin-independent case. [Copyright &y& Elsevier]

Highlights: [•] Validates TALYS-1.4 code for calculating (n,p) cross-sections in mid mass region. [•] Importance of pre-equilibrium emission in (n,p) reaction from threshold to 20MeV. [•] Pre-equilibrium contribution is 90–99% for Gd and 83–85% for Dy isotopes at 14.7MeV. [ABSTRACT FROM AUTHOR]

Heavy quark RAA and v2 has been calculated at Relativistic Heavy Ion Collider energy considering initial conditions with and without pre-equilibrium phase to highlight the effect of the latter on heavy quark observables. The momentum evolution of the heavy quark has been studied by means of the Boltzmann transport equation. To model the pre-equilibrium phase we have used the KLN initial condition. We found that the pre-equilibrium phase impacts the RAA by about 20%–25% whereas the impact on v2 is very negligible. We also calculated heavy quark RAA and v2 in the case of initializations with early thermalized quark–gluon plasma (QGP). We checked that the particular form of the initial spectrum is not very important for RAA, the larger energy density being more important. In fact, comparing the results obtained within the two initializations we found that one can mimic the impact of the pre-equilibrium phase using an early thermalized QGP medium. [ABSTRACT FROM AUTHOR]

The drag and diffusion coefficients of heavy quarks (HQs) have been evaluated in the pre-equilibrium phase of the evolving fireball produced in heavy ion collisions at relativistic heavy ion collider and Large Hadron Collider energies. KLN and classical Yang–Mills spectra have been used for describing the momentum distributions of the gluons produced just after the collisions but before they thermalize. The interaction of the HQs with these gluons has been treated within the framework of perturbative quantum chromodynamics. We have observed that the HQs are dragged almost equally by the kinetically equilibrated and out-of-equilibrium gluonic systems. We have also noticed that the HQ diffusion in the pre-equilibrium gluonic phase is as fast as in the kinetically equilibrated gluons. Moreover, the diffusion is faster in the pre-equilibrium phase than in the chemically equilibrated quark–gluon plasma. These findings may have significant impact on the analysis of experimental results on the elliptic flow and the high momentum suppression of the open charm and beauty hadrons. [ABSTRACT FROM AUTHOR]