Projectile Breakup Research Articles

Coupled channel effect in elastic scattering and fusion for6,7Li+28Si

The fusion excitation and elastic angular distribution were measured for 6,7 Li+28 Si from below to above Coulomb barrier (≤ 3Vb ) energies. The barrier distribution derived from the fusion data was found to be broad and asymmetric at the sub-barrier region, compared to 1D BPM estimation. Effect of rotational coupling on fusion was found to be not so dominant. Phenomenological optical potential parameters, with surface and volume type imaginary potentials, were obtained from f tting of elastic scattering data and energy dependence of real and imaginary surface strengths were investigated around the barrier. CDCC calculations considering only breakup of projectile were performed for 6,7 Li+28 Si with the elastic scattering data, using the code FRESCO. The effects of breakup of projectile on elastic cross section do not agree with the energy dependence of real and imaginary strength with volume type imaginary potential around the barrier.

Measurement and analysis of excitation functions and observation of mass-asymmetry effect on incomplete fusion dynamics

Excitation functions for sixteen evaporation residues produced in the interaction of 20 Ne with 165 Ho have been measured in the projectile energy range ≈88-164 MeV, using catcher foil activation technique followed by gamma-ray spectrometry. It has been found in general that the excitation functions of evaporation residues produced via xn/pxn channels satisfactorily reproduced with the statistical model code PACE-2 after subtraction of precursor decay contribution. The significant enhancement in the measured excitation functions for the residues produced in alpha emission channels over the PACE-2 predictions has been observed. These alpha emission channels are attributed to incomplete fusion reaction process. The results indicate the occurrence of incomplete fusion involving break-up of projectile 20 Ne into 4 He + 16 O and /or 8 Be + 12 C followed by fusion of one of the fragments with target nucleus 165 Ho. The analysis of the present data suggest that probability of incomplete fusion increases with projectile energy. The ICF fraction F ICF also increases with increasing mass-asymmetry of the entrance channel.

Influence of projectile breakup on complete fusion

Complete fusion excitation functions for 11,10B+159Tb and 6,7Li+159Tb have been reported at energies around the respective Coulomb barriers. The measurements show significant suppression of complete fusion cross-sections at energies above the barrier for 10B+159Tb and 6,7Li+159Tb reactions, when compared to those for 11B+159Tb. The comparison shows that the extent of suppression of complete fusion cross-sections is correlated with the α-separation energies of the projectiles. Also, the measured incomplete fusion cross-sections show that the α-particle emanating channel is the favoured incomplete fusion process. Inclusive measurement of the α-particles produced in 6Li+159Tb reaction has been carried out. Preliminary CDCC calculations carried out to estimate the α-yield following 6Li breaking up into α+d fail to explain the measured α-yield. Transfer processes seem to be important contributors.

Projectile breakup dynamics for 6Li + 59Co : Kinematical analysis of $ \alpha$ - d coincidences

A study of the kinematics of the $ \alpha$ -d coincidences in the 6Li + 59Co system at a bombarding energy of E lab = 29.6 MeV is presented. With exclusive measurements performed over different angular intervals it is possible to identify the respective contributions of the sequential and direct projectile breakup components. The angular distributions of both breakup components are fairly well described by the Continuum-Discretized Coupled-Channels framework (CDCC). Furthermore, a careful analysis of these processes using a semiclassical approach provides information on both their lifetime and their distance of occurrence with respect to the target. Breakup to the low-lying (near-threshold) continuum is delayed, and happens at large internuclear distances. This suggests that the influence of the projectile breakup on the complete fusion process can be related essentially to the direct breakup to the 6Li high-lying continuum spectrum.

Probing the 6,7Li nucleon densities through a new break-up process approach

In this work we present a double folding optical model analysis of new near-barrier quasi-elastic experimental data for the 6,7Li + 120Sn systems. From the analysis, it was possible to confirm the ground-state nucleon densities assumed for the weakly bound 6,7Li isotopes. The apparent discrepancies between the experimental densities and those based on Dirac–Hartree–Fock–Bogoliubov (DHB) calculations were removed. A new approach that simulates the projectile break-up and a positive polarization from couplings of 6,7Li bound states with the continuum was considered in the reaction mechanism.

Extended optical model analyses for the 11B + 209Bi system at near-Coulomb-barrier energies

In the framework of an extended optical model approach in which the polarization potential is decomposed into direct-reaction (DR) and fusion parts, simultaneous \( \chi^{{2}}_{}\) analyses of elastic scattering and fusion cross-section data for the 11B$ + $209Bi system at near-Coulomb-barrier energies are performed. We show that the DR and fusion potentials extracted from \( \chi^{{2}}_{}\) analyses separately satisfy the dispersion relation and that the threshold anomaly exhibits in both DR and fusion parts. We find that the analyses using only elastic scattering and fusion data can produce reliable predictions of cross-sections even though the direct reaction cross-section data are not complete. By using the extracted DR potential, we investigate the effects of the projectile breakup on fusion cross-sections.

Breakup coupling effects on near-barrier quasi-elastic scattering ofLi6,7onSm144

Excitation functions of quasi-elastic scattering at backward angles have been measured for the $^{6,7}\mathrm{Li}+^{144}\mathrm{Sm}$ systems at near-barrier energies, and fusion barrier distributions have been extracted from the first derivatives of the experimental cross sections with respect to the bombarding energies. The data have been analyzed in the framework of continuum discretized coupled-channel calculations, and the results have been obtained in terms of the influence exerted by the inclusion of different reaction channels, with emphasis on the role played by the projectile breakup.

Resonant breakup of 6Li by 209Bi

The exclusive projectile breakup cross section in the Li6+Bi209 reaction has been measured at Elab=40 and 36 MeV. The sequential breakup, via the resonant state (3+, 2.18 MeV) of 6Li in the continuum, dominates the total α+d breakup. The inclusive breakup α cross section is, however, much larger implying that other competing breakup processes contribute to the α-particle yields. The corrected yields corresponding to two sequential breakup peaks in the α or d spectra were seen to be asymmetric. The average sequential breakup data corresponding to the resonant state are in good agreement with continuum discretized coupled channels (CDCC) calculations. Both Coulomb as well as nuclear field effects were found to be important for the breakup process.

Four-body calculation ofHe6breakup with the Coulomb-corrected eikonal method

The elastic breakup of a three-body projectile on a target is studied within the eikonal approximation with full account of final-state interactions. Bound and scattering states are calculated in hyperspherical coordinates on a Lagrange mesh. A correction is introduced to avoid the divergence of breakup cross sections due to the Coulomb interaction. The eikonal approximation allows the direct calculation of various cross sections, and in particular multidifferential cross sections can be obtained. The model is applied to the breakup of {sup 6}He on {sup 208}Pb. The {sup 6}He halo nucleus is described within a three-body {alpha}+n+n model involving effective {alpha}n and nn interactions. The eikonal phase is obtained from optical potentials between {alpha} and n, and the target. Around 0.8 MeV, the total breakup cross sections exhibit a narrow 2{sup +} resonant peak superimposed over a broad bump corresponding to a 1{sup -} resonance. These results suffer from a disagreement with experimental data at 240 MeV/nucleon, where cross sections are much smaller at low energies. The obtained E1 strength distribution resembles other theoretical results and reopens a long-standing problem about the existence of a 1{sup -} low-energy resonance in the {sup 6}He continuum.

Generalized optical potential for weakly bound nuclei: Two-cluster projectiles

A generalized optical potential for elastic scattering induced by light nuclei is calculated within the Feshbach projection operator method. The model explicitly takes into account the contribution of the projectile breakup continuum treated within a microscopic few-cluster model. In this work, we formulate the model, deriving an explicit expression for the optical potential, and demonstrate the ability of the model by applying it to deuteron elastic scattering.

Reaction cross sections forB8,Be7, andLi6+Ni58near the Coulomb barrier: Proton-halo effects

Elastic scattering of $^{8}\mathrm{B}$, $^{7}\mathrm{Be}$, and $^{6}\mathrm{Li}$ on a $^{58}\mathrm{Ni}$ target has been measured at energies near the Coulomb barrier. Optical-model fits were made to the experimental angular distributions, and total reaction cross sections were deduced. A comparison with other systems provides striking evidence for proton-halo effects on $^{8}\mathrm{B}$ reactions. As opposed to the situation for the neutron-halo nucleus $^{6}\mathrm{He}$, for which particle transfer dominates, the ``extra'' cross section observed for $^{8}\mathrm{B}$ appears to result entirely from projectile breakup.

Coulomb-corrected eikonal description of the breakup of halo nuclei

The eikonal description of breakup reactions diverges because of the Coulomb interaction between the projectile and the target. This divergence is due to the adiabatic, or sudden, approximation usually made, which is incompatible with the infinite range of the Coulomb interaction. A correction for this divergence is analyzed by comparison with the dynamical eikonal approximation, which is derived without the adiabatic approximation. The correction consists in replacing the first-order term of the eikonal Coulomb phase by the first-order of the perturbation theory. This allows taking into account both nuclear and Coulomb interactions on the same footing within the computationally efficient eikonal model. Excellent results are found for the dissociation of $^{11}\mathrm{Be}$ on lead at 69 MeV/nucleon. This Coulomb-corrected eikonal approximation provides a competitive alternative to more elaborate reaction models for investigating breakup of three-body projectiles at intermediate and high energies.

GENERALIZED OPTICAL POTENTIAL OF LIGHT WEAKLY BOUND CLUSTER NUCLEI

A generalized optical potential for elastic scattering induced by light weakly bound nuclei is calculated within the Feshbach projection operator method. The model explicitly takes into account the contribution of the projectile break-up continuum treated within a microscopic cluster model. The model is tested on deuteron and 6Lielastic scattering by different targets at intermediate energies. The optical potentials are then calculated for the 6 He(230 MeV) +12Creaction treating the projectile nuclei within two (α + 2n) and three (α + n + n) cluster models. The differences are analyzed.

Level structure of the odd–odd nucleus 54Mn

The energy levels of 54Mn were populated by a 145 MeV 20Ne beam incident on a 51V target nucleus. This, difficult to access, N = 29 nucleus was produced by projectile break-up followed by incomplete fusion of an alpha particle. The de-exciting gamma transitions were detected using a multi-clover array: Indian National Gamma Array (INGA). The level structure of 54Mn has been extended up to E* ≅ 5 MeV and Jπ = 15+ with an addition of nine new γ-transitions. The absence of any regular band-like structure in 54Mn indicates the dominance of the single-particle nature of this odd–odd nucleus. The polarization measurements indicate the possibility of a negative-parity level at 1925 keV.

Elastic scattering on a nucleus and the breakup of the composite projectile via wave-packet continuum discretization

The scattering of a composite particle off a nucleus with account of the breakup effect is solved via the original formalism of the stationary wave packets. The approach is based on the integral equation formalism of the scattering theory with a complete discretization of the three-body continuum. This allows one to find the elastic and breakup amplitudes from one nonsingular matrix equation and also to use a very convenient ${L}_{2}$ basis in numerical calculations. The efficiency of the approach is demonstrated by a realistic example of deuteron scattering on a ${}^{58}\mathrm{Ni}$ target.

Appropriate bare potentials for studying fusion induced byHe6

We analyze fusion cross sections induced by the $^{6}\mathrm{He}$ halo projectile in the framework of the double-folding S\~ao Paulo potential, which has already been shown to be a reliable potential for the analysis of fusion cross sections induced by stable weakly bound nuclei. The results show that the fusion cross sections of $^{6}\mathrm{He}+^{209}\mathrm{Bi}$, $^{238}\mathrm{U}$, $^{64}\mathrm{Zn}$ are suppressed at energies above the barrier when compared with coupled-channels calculations that do not take into account the projectile breakup, whereas they are in agreement with the calculations at subbarrier energies. The results for the $^{6}\mathrm{He}+^{209}\mathrm{Bi}$ system are contradictory to those reported previously.

Hindrance of fusion induced by 6He

We analyze fusion cross sections induced by the 6 He halo projectile in the framework of the double folding Sao Paulo potential, which has been shown to be a reliable potential for the analysis of fusion cross sections induced by stable weakly bound nuclei. The results show that the fusion cross sections of 6 He + 209 Bi, 238 U are suppressed at energies above the barrier, when compared with coupled channel calculations that do not take into account the projectile breakup, whereas they are in agreement with the calculations at sub-barrier energies.

Reaction mechanisms with loosely bound nucleiLi7+Li6at forward angles in the incident energy range 14–20 MeV

Emission of charged particles from the $^{7}\mathrm{Li}$+$^{6}\mathrm{Li}$ reaction at $E$($^{7}\mathrm{Li}$$)=14\text{\ensuremath{-}}20$ MeV is studied at forward angles. Analysis of the inclusive spectra are performed in terms of the statistical model for compound nuclear process and Serber model for inclusive breakup reactions. Compound nuclear calculations better reproduce the experimental data in comparison to the projectile breakup calculations even at extreme forward angles and above barrier energies.

Production of 3He and 6He fragments in the interaction of 12C with 93Nb at 400 MeV

Spectra of inclusive double differential cross sections of 3He and 6He fragments produced in the interaction of 12C with 93Nb at 400 MeV are measured and analyzed. As was found for the production of intermediate mass fragments in this and similar reactions involving light projectiles, the spectra can to a large extent be satisfactorily reproduced only by considering the contribution of projectile break-up as well as nucleon coalescence.

Two-neutron transfer in theHe6+Bi209reaction near the Coulomb barrier

The cross section for \ensuremath{\alpha}-particle emission in the $^{6}\mathrm{He}+^{209}\mathrm{Bi}$ reaction at energies near the Coulomb barrier is remarkably large. Possible reactions that may produce the observed \ensuremath{\alpha} particles include two-neutron transfer, one-neutron transfer, and direct projectile breakup. Each of these mechanisms results in a distinctive angular correlation between the \ensuremath{\alpha} particle and the outgoing neutron(s). A neutron-\ensuremath{\alpha}-particle coincidence experiment was performed to study two-neutron transfer to unbound states of $^{211}\mathrm{Bi}$. It is shown that approximately 55% of the observed \ensuremath{\alpha}-particle yield at and beyond the grazing angle is because of this process. This is more than 2.5 times the fraction attributable to single-neutron transfer. The corresponding 2n-transfer cross section is 0.4 \ifmmode\pm\else\textpm\fi{} 0.1 b.