Showing papers by "V. V. Parkar published in 2011"

Fusion of Li 6 with Tb 159 at near-barrier energies

Abstract: Complete and incomplete fusion cross sections for $^{6}\mathrm{Li}$ $+$ $^{159}\mathrm{Tb}$ have been measured at energies around the Coulomb barrier by the $\ensuremath{\gamma}$-ray method. The measurements show that the complete fusion cross sections at above-barrier energies are suppressed by $~$34% compared to coupled-channel calculations. A comparison of the complete fusion cross sections at above-barrier energies with the existing data for $^{11,10}\mathrm{B}$ $+$ $^{159}\mathrm{Tb}$ and $^{7}\mathrm{Li}$ $+$ $^{159}\mathrm{Tb}$ shows that the extent of suppression is correlated with the $\ensuremath{\alpha}$ separation energies of the projectiles. It has been argued that the Dy isotopes produced in the reaction $^{6}\mathrm{Li}$ $+$ $^{159}\mathrm{Tb}$ at below-barrier energies are primarily due to the $d$ transfer to unbound states of $^{159}\mathrm{Tb}$, while both transfer and incomplete fusion processes contribute at above-barrier energies.

Reaction mechanisms involving weakly bound Li 6 and Bi 209 at energies near the Coulomb barrier

Abstract: The elastic, inelastic, and transfer cross sections are measured for the ${}^{6}\mathrm{Li}+{}^{209}\mathrm{Bi}$ reaction at energies around the Coulomb barrier. The optical model analysis of elastic scattering shows a breakup threshold anomaly in the energy dependence of the real and imaginary potentials. The observed energy dependence is found to be consistent with the dynamic polarization potential obtained from the coupled-channels calculations that explain the above measured reaction channels simultaneously. A comparison of different reaction probabilities reveals that the relative contribution of breakup starts increasing at energies below the Coulomb barrier, in contrast to the behavior of other reaction channels, which get closed as energy is lowered. The large probability of projectile breakup at sub-Coulomb energies leads to the observation of a nonzero imaginary potential even at ${E}_{\text{lab}}\ensuremath{\leqslant}0.8{V}_{B}$.

Investigation of cluster structure of 9 Be from high precision elastic scattering data

Abstract: The cluster structure of ${}^{9}$Be has been investigated through high precision elastic scattering cross-section measurements of a ${}^{9}$Be $+$ ${}^{208}$Pb system at below barrier energies, $E=$ 24--34 MeV.The observed deviation from the Rutherford scattering can only be explained by an $n$ $+$ ${}^{8}$Be cluster description of ${}^{9}$Be, whereas the $\ensuremath{\alpha}$ $+$ ${}^{5}$He cluster picture fails to explain the measured data, indicating the dominance of the $n$ $+$ ${}^{8}$Be cluster structure of ${}^{9}$Be. In addition to sequential and direct breakup, the coupling effect of one neutron stripping on elastic scattering is significant even at 10 MeV below the barrier. The sensitivity of the high precision elastic scattering data to the cluster structure of ${}^{9}$Be has been demonstrated.

Coupled channel effect in elastic scattering and fusion for 6,7Li+28Si

Abstract: 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.

Fusion of $^8$He with $^{206}$Pb around Coulomb barrier energies

Abstract: The experimental study of the fusion of light neutron-rich nucleus 8 He with 206 Pb is reported in this work. A fusion stack of 206 Pb targets has been used for this study. The most prominent evaporation residue ( 210 Po), which has half-life of 138 days and decays by alpha emission, is populated in the reaction. Radiochemical analysis technique is used to extract the yield of this evaporation residue.

Study of fusion in 6,7Li+197Au at near barrier energies

Abstract: Excitation functions are measured for complete fusion and transfer reactions of 6 Li and 7 Li with 197 Au at energies around the Coulomb barrier. Coupled channel calculations including the couplings to both target and projectile excited states have been performed and are found to explain the data at energies below the barrier. At above barrier energies the complete fusion cross sections are found to be suppressed compared to the coupled channel calculations for both the systems. A systematic comparison of fusion cross-section for halo nuclei 6,8 He and weakly bound stable nuclei 6,7 Li on 197 Au target is also presented. Large neutron transfer cross-sections are observed for 6,7 Li as compared to tightly bound projectiles 12 C, 16 O.

Study of reactions with the weakly bound projectile 9 Be with 89 Y

Abstract: With the aim to investigate the in∞uence of the breakup channel on difierent reaction channels, the elastic scattering and fusion of 9 Be with the medium mass target 89 Y has been stud- ied at near barrier energies. Optical model analysis of the elastic data has been carried out and a dispersion relation applied to the real and imaginary potentials to investigate their energy depen- dence from which the presence of breakup threshold anomaly has been observed. Complete fusion (CF) cross sections, obtained for 9 Be+ 89 Y system, are found to be suppressed by (20 § 5)% as compared to the coupled-channels calculations without breakup coupling. This observation has been further conflrmed by comparing these cross sections with those for the 4 He+ 93 Nb and 12 C+ 89 Y systems, where fusion is induced by a tightly bound projectile and forms a nearby compound nu- cleus to that formed by 9 Be+ 89 Y. Results from the breakup coupling done in continuum discretized coupled-channels calculations show that the elastic cross sections thus obtained, which also flt the experimental elastic cross sections, are enhanced compared to the uncoupled calculations which im- plies a reduction in absorption/fusion cross sections. These enhanced cross sections suggest that the dynamic polarization potential produced due to breakup coupling is repulsive in nature. Thus the efiective (bare+polarization) potential around the barrier becomes less attractive leading to the absence of the normal threshold anomaly.

Complete and incomplete fusion in 9Be+124Sn system

Abstract: Abstract Complete and incomplete fusion cross-sections for the 9Be+124Sn system have been measured around the Coulomb barrier energies (ElabC.B=28 MeV) using the on-line gamma ray detection technique. The complete fusion cross-sections of this system have been compared with the two stable projectiles on the same 124Sn target to provide information on the projectile dependence. The brief comparison of the present 9Be+124Sn data with a comprehensive and recent study of the neighbouring system 9Be+144Sm is also given.