Extended Hauser-Feshbach method for statistical binary decay of light-mass systems

Abstract

An Extended Hauser-Feshbach Method (EHFM) is developed for light heavy-ion fusion reactions in order to provide a detailed analysis of all the possible decay channels by including explicitly the fusion-fission phase-space in the description of the cascade chain. The mass-asymmetric fission component is considered as a complex-fragment binary-decay which can be treated in the same way as the light-particle evaporation from the compound nucleus in statistical-model calculations. The method of the phase-space integrations for the binary-decay is an extension of the usual Hauser-Feshbach formalism to be applied to the mass-symmetric fission part. The EHFM calculations include ground-state binding energies and discrete levels in the low excitation-energy regions which are essential for an accurate evaluation of the phase-space integrations of the complex-fragment emission (fission). In the present calculations, EHFM is applied to the first-chance binary-decay by assuming that the second-chance fission decay is negligible. In a similar manner to the description of the fusion-evaporation process, the usual cascade calculation of light-particle emission from the highly excited complex fragments is applied. This complete calculation is then defined as EHFM+CASCADE.Calculated quantities such as charge-, mass-and kinetic-energy distributions are compared with inclusive and/or exclusive data for the 32 S+ 24 Mg and 35 Cl+ 12 C reactions which have been selected as typical examples. Finally, the missing charge distributions extracted from exclusive measurements are also successfully compared with the EHFM+CASCADE predictions.

Emission of intermediate mass fragments from hot116Ba* formed in low-energy58Ni +58Ni reaction

“…The neck-length parameter δR(β i ), introduced at the scission configuration, simulates the two-centre nuclear shape parametrization and is equivalent to the lowering of the barrier for the case of deformed fragments [27]. This method of inclusion of fragment deformations in the present calculations is quite similar to what has been achieved in both the saddle-point transition-state model of Sanders [3,4] and the scission-point Extended Hauser-Feshbach Method of Matsuse and collaborators [5]. The work of Ref.…”

“…Thus, for a given E c.m. , ∆R is fixed for all the fragments; on the other hand ∆R was fitted for each fragment separately in our earlier work [10], as well as in the statistical model calculations of other authors [4,5]. Note, the ∆R in our model is the same as the neck length parameter d in Refs.…”

“…(5), ∆R depends on η. In the following, however, based on our earlier works [10,22] and the works of other authors [4,5] (discussed later), we use a constant average value ∆R, independent of η, which also takes care of the additional δR(β i ) effects of the deformations of fragments and neck formation between them. The ∆R is the only parameter of the model, though we shall see later that the structure of the calculated (s-wave) mass spectrum is nearly independent of the exact choice of this parameter value.…”

“…complex fragments with masses lighter than A<20, are emitted from both the light (A∼60) and medium-mass (A∼110) compound systems, and may arise as multiple "clusters", and are accompanied by multiple light particles (Z≤2) production. This light-particle emission, associated with evaporation residues production, is very satisfactorily understood as the fusion-evaporation process from an equiliberated compound nucleus in the statistical Hauser-Feshbach formalism [1,2,3,4,5], described in evaporation codes such as LILITA and CASCADE or many other codes. The Hauser-Feshbach formalism has been extended to include the above noted observed complex IMFs, for example in the BUSCO code [2] or in the Extended Hauser-Feshbach Method based on the scission-point picture [5].…”

“…This light-particle emission, associated with evaporation residues production, is very satisfactorily understood as the fusion-evaporation process from an equiliberated compound nucleus in the statistical Hauser-Feshbach formalism [1,2,3,4,5], described in evaporation codes such as LILITA and CASCADE or many other codes. The Hauser-Feshbach formalism has been extended to include the above noted observed complex IMFs, for example in the BUSCO code [2] or in the Extended Hauser-Feshbach Method based on the scission-point picture [5]. An alternative process for the IMFs production is the binary decay of a compound nucleus in the statistical fission model of Moretto [6] or of Vandenbosch and Huizenga [7].…”