Systematic description of evaporation spectra for light and heavy compound nuclei

Abstract

To systematically describe evaporation spectra for light and heavy compound nuclei over a large range of excitation energies, it was necessary to consider three ingredients in the statistical model. Firstly, transmission coefficients or barrier penetration factors for charged-particle emission are typically taken from global fits to elastic-scattering data. However, such transmission coefficients do not reproduce the barrier region of evaporation spectra and reproduction of the data requires a distributions of Coulomb barriers. This is possibly associated with large fluctuations in the compound-nucleus shape or density profile. Secondly for heavy nuclei, an excitation-energy dependent level-density parameter is required to describe the slope of the exponential tails of these spectra. The level-density parameter was reduced at larger temperatures, consistent with the expected fadeout of long-range correlation, but the strong A dependence of this effect is unexpected. Lastly to describe the angular-momentum dependence of the level density in light nuclei at large spins, the macroscopic rotational energy of the nucleus has to be reduced from the values predicted with the Finite-Range Liquid-Drop model.where J d is the spin of the daughter nucleus, S i , J, and ℓ, are the spin, total and orbital angular momenta of the evaporated particle, ε and B i are is its kinetic and separation energies, T ℓ is its transmission coefficient or

Reaction mechanisms and staggering in collisions

“…The purpose of the calculation being simply to enlighten the physical mechanism leading to the presence (absence) of odd-even effects in the different thermodynamic conditions, we have simply fixed in the GEMINI [34] evaporation model a source with Gaussian-distributed parameters with E * = 1 A MeV, σ E * = 0.1 A MeV, Z = 16 and σ Z = 1. The source mass number is then fixed as A = 2Z.…”

Transport properties of isospin asymmetric nuclear matter using the time-dependent Hartree-Fock method

“…It is expected that the primary fragments will undergo various processes to approach the β −stability line in time [16]. However, assuming that it is statistical in character, the deexcitation process can be calculated with programs like GEMINI [85,86] provided realistic inputs can be obtained. In addition to the mass and charge of the PLF we calculate the excitation energy of each primary fragment (discussed in the next section) as well as the angular momentum "loss" (i.e., transfer from initial orbital angular momentum to intrinsic angular momentum of the fragments).…”

Non-equilibrium processes in p + Ag collisions at GeV energies

“…The first, nonequilibrium step of the process was described by the INCL4.6 model [17], which takes into consideration the intranuclear cascade of nucleon-nucleon and nucleon-pion collisions as well as the emission of complex particles created due to the coalescence of the nucleon escaping from the cascade with other nucleons which are sufficiently close to it in the coordinate and momentum space. The deexcitation of the equilibrated remnant of the first stage of the reaction was calculated by means of four different models, namely, GEM2 [21,22], ABLA07, [23], GEMINI++ [28][29][30], and SMM [24][25][26][27].…”

“…The INCL4.6 model [17] was used for this purpose. The emission of particles from equilibrated target remnants of the first stage of the reaction was calculated using four different models: the generalized evaporation model GEM2 of Furihata [21,22], the ABLA07 statistical model of Kelić et al [23], the statistical multifragmentation model (SMM) of Botvina et al [24][25][26][27], and the sequential binary decay model GEMINI++ of Charity [28][29][30].…”

“…The deexcitation of large fragments (with mass number larger than 16) is described by the evaporation-fission model, whereas that of smaller fragments is described by the Fermi break-up model [27]. The GEMINI++ code by Charity [28][29][30] is a modified version of GEMINI [33] which describes the deexcitation of the compound nucleus by sequential binary decays proceeding until the final products are unable to undergo further division. The Hauser-Feshbach formalism is used to describe an asymmetric decay of the compound nucleus resulting in the emission of light particles (with Z up to 4), whereas Moretto's generalized transition-state formalism [34] is applied to heavier asymmetric divisions.…”