Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userEffects of unconventional breakup modes on incomplete fusion of weakly bound nuclei
178
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The incomplete fusion dynamics of $^6$Li + $^{209}$Bi collisions at energies above the Coulomb barrier is investigated. The classical dynamical model implemented in the {sc platypus} code is used to understand and quantify the impact of both $^6$Li resonance states and transfer-triggered breakup modes (involving short-lived projectile-like nuclei such as $^8$Be and $^5$Li) on the formation of incomplete fusion products. Model calculations explain the experimental incomplete-fusion excitation function fairly well, indicating that (i) delayed direct breakup of $^6$Li reduces the incomplete fusion cross-sections, and (ii) the neutron-stripping channel practically determines those cross-sections.
rate research
Read More
The optical potential of halo and weakly bound nuclei has a long range part due to the coupling to breakup that damps the elastic scattering angular distributions. In order to describe correctly the breakup channel in the case of scattering on a heavy target, core recoil effects have to be taken into account. We show here that core recoil and nuclear breakup of the valence nucleon can be consistently taken into account. A microscopic absorptive potential is obtained within a semiclassical approach and its characteristics can be understood in terms of the properties of the halo wave function and of the reaction mechanism. Results for the case of medium to high energy reactions are presented.
The classical dynamical model for reactions induced by weakly-bound nuclei at near-barrier energies is developed further. It allows a quantitative study of the role and importance of incomplete fusion dynamics in asymptotic observables, such as the population of high-spin states in reaction products as well as the angular distribution of direct alpha-production. Model calculations indicate that incomplete fusion is an effective mechanism for populating high-spin states, and its contribution to the direct alpha production yield diminishes with decreasing energy towards the Coulomb barrier. It also becomes notably separated in angles from the contribution of no-capture breakup events. This should facilitate the experimental disentanglement of these competing reaction processes.
The inclusive breakup of three-fragment projectiles is discussed within a four-body spectator model. Both the elastic breakup and the non-elastic breakup are obtained in a unified framework. Originally developed in the 80s for two-fragment projectiles such as the deuteron, in this paper the theory is successfully generalized to three-fragment projectiles. The expression obtained for the inclusive cross section allows the extraction of the incomplete fusion cross section, and accordingly generalizes the surrogate method to cases such as (t,p) and (t,n) reactions. It is found that two-fragment correlations inside the projectile affect in a conspicuous way the elastic breakup cross section. The inclusive non-elastic breakup cross section is calculated and is found to contain the contribution of a three-body absorption term that is also strongly influenced by the two-fragment correlations. This latter cross section contains the so-called incomplete fusion where more than one compound nuclei are formed. Our theory describes both stable weakly bound three-fragment projectiles and unstable ones such as the Borromean nuclei.
The influence on the fusion process of coupling to collective degrees of freedom has been explored. The significant enhancement of he fusion cross setion at sub-barrier energies was understood in terms of the dynamical processes arising from strong couplings to collective inelastic excitations of the target and projectile. However, in the case of reactions where breakup becomes an important process, conflicing model predictions and experimental results have been reported in the literature. Excitation functions for sub- and near-barrier total (complete + incomplete) fusion cross sections have been measured for the $^{6,7}$Li + $^{59}$Co at the Vivitron facility and at the 8UD Pelletron tandem facility using standard $gamma$-ray techniques. The data extend to medium-mass systems previous works exploring the coupling effects in fusion reactions of both lighter and heavier systems. Results of continuum-discretized coupled channel (CDCC) calculations indicate a small enhancement of total fusion for the more weakly bound $^{6}$Li at sub-barrier energies, with similar cross sections for both reactions at and above the barrier. A systematic study of $^{4,6}$He induced fusion reactions with the CDCC method is in progress. The understanding of the reaction dynamics involving couplings to the breakup channels requires th explicit measurement of precise elastic scattering data as well as yields leading to the breakup itself. Recent coincidence experiments for $^{6,7}$Li + $^{59}$Co are addressing this issue. The particle identification of the breakup products have been achieved by measuring the three-body final-state correlations.
A self-contained Fortran-90 program based on a classical trajectory model with stochastic breakup is presented, which should be a powerful tool for quantifying complete and incomplete fusion, and breakup in reactions induced by weakly-bound two-body projectiles near the Coulomb barrier. The code calculates complete and incomplete fusion cross sections and their angular momentum distribution, as well as breakup observables (angle, kinetic energy and relative energy distributions).
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
