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Enhancement of fusion cross sections below the interaction barrier has been quite successfully explained by coupled-channels methods. However, extending the measurements to deep sub-barrier energies revealed a steeper descent of the excitation function which could not be explained by standard coupled-channels calculations. Though a large number of heavy-ion and light-ion induced reactions have been investigated to understand the dynamics of fusion deep below the barrier, the phenomenon of fusion hindrance has been studied only for a handful of asymmetric systems. We report new measurements of fusion excitation functions for the systems 16O+116Cd and 16O+142Ce. We also present comparisons of the same with the data for existing symmetric systems having nearly similar values of the ζ parameter, characterizing the size of the colliding system. We extracted the logarithmic derivatives of the energy-weighted cross sections and the astrophysical S -factors. Experimental results were reproduced well by coupled-channels calculations. We extrapolated our results, following the systematics, beyond the threshold energy for fusion hindrance for both the systems. From our investigation, we conclude that the present asymmetric systems, as well as the corresponding symmetric systems, show fusion hindrance and this feature is independent of the entrance channel mass asymmetry.

The state-of-the-art technologies made it possible to reach the realms of fusion between two complex nuclei that offer an opportunity to explore a diverse spectrum of fusion phenomena. In this article, we have reported the influence of positive Q-value neutron transfer (PQNT) channels in fusion dynamics. Significant enhancement in sub-barrier fusion cross section has been observed for the 28Si+158Gd as compared to 30Si+140Ce and other similar systems with nearby mass asymmetry. Current findings include a comparison of the fusion excitation function of multiple systems on a reduced scale. The study sheds light on the influence of PQNT channels and deformation in nuclei on the sub-barrier fusion phenomenon. Further, fusion barrier parameters (barrier height and radius) extracted from the measured data demonstrate a good agreement with the empirical parameterization and proximity potential models.

Fusion cross-section measurements were performed for system 40Ca + 70Zn around the Coulomb barrier energies using Heavy Ion Reaction Analyzer (HIRA). The observed enhancement in experimental fusion cross-sections was investigated via coupled-channels formalism. The coupling of inelastic excitations alone could not reproduce the experimental data, however, the effect of octupole state of the projectile was observed to be significant. The multi-neutron positive Q-value transfer channels were also included in the calculations using semi-classical model. It was observed that two neutrons pick-up channel gave a major contribution to the fusion enhancement and successfully reproduce the experimental data at above as well as below barrier energies. The coupling of more than two neutrons transfer could not give any significant enhancement to subbarrier fusion.

Present work aims to explicate the effect of entrance channel mass asymmetry on fusion dynamics for the Compound Nucleus 80Sr populated through two different channels, 16O+64Zn and 32S+48Ti, using cross-section and spin distribution measurements as probes. The evaporation spectra studies for these systems, reported earlier indicate the presence of dynamical effects for mass symmetric 32S+48Ti system.The CCDEF and TDHF calculations have been performed for both the systems and an attempt has been made to explain the reported deviations in the α-particle spectrum for the mass symmetric system.

Investigations of complete fusion reactions leading to the synthesis of heavy and superheavy nuclei have been an important part of the experimental program at the Flerov Laboratory of Nuclear Reactions (JINR, Dubna). For synthesis and decay studies of heavy nuclei, a project of modernization of the existing experimental set up VASSILISSA is now underway. The results of the first experimental tests with the modernized VASSILISSA separator are presented, in particular the experimentally measured transmission coefficients for recoil nuclei synthesized in asymmetric reactions with a 22Ne beam. These results completely confirm the ion optical calculations performed during the design stage of the modernization.

The spin distributions are measured for the compound nucleus 80Sr populated in the reactions 16O+64Zn and 32S+48Ti. The comparison of the experimental results for both the systems shows that the mean γ-ray multiplicity values for the system 32S+48Ti are lower than those for 16O+64Zn. The spin distribution of the compound nucleus populated through the symmetric channel is also found to be lower than the asymmetric channel. Present investigation directly shows the effect of entrance channel mass asymmetry on the reaction dynamics.

We present the evolution of giant dipole resonance (GDR) width as a function of angular momentum in the compound nucleus 144Sm in the temperature range of 1.5-2.0 MeV. The high energy γ rays emitted from the decay of excited 144Sm were measured using large NaI detector in coincidence with 4π sum spin spectrometer. GDR widths were found to comply with thermal shape fluctuation model in this temperature range over a wide range of spin. Experimental widths tend to increase rapidly at high angular momentum values.

Exclusive measurement of giant dipole resonance (GDR) γ rays has been performed in 144Sm nucleus which was populated at near barrier energy using the heavy ion reaction of 28Si beam on 116Cd target. GDR γ rays were detected in coincidence with low energy γ rays using 32 elements 4π sum-spin spectrometer. The 144Sm nucleus was populated at an excitation energy of 68 MeV in the temperature range of 1.1-1.3 MeV. The measured GDR widths in this temperature range are consistent with the Kusnezov’s parametrization.

The Hybrid Recoil mass Analyzer (HYRA) operated in gas-filled mode has recently been coupled with the TIFR 4π spin spectrometer at IUAC, New Delhi to carry out spin (or angular momentum) distribution of heavy residues from fusion-evaporation reactions and spin gated GDR measurements. The details of the combined facility, initial experiments on evaporation residue tagged γ-multiplicity and the extraction of average transmission efficiency of HYRA are elaborated.

The spin distribution of Evaporation Residues (ER) was measured for the reaction 30Si + 170Er. ER spin distributions were compared for the systems 16O + 184W, 19F + 181Ta and 30Si + 170Er forming the Compound Nucleus 200Pb. Mean gamma multiplicity vs. excitation energy curve shows saturation at a lower value in case of 30Si + 170Er. This was attributed to non compound nuclear processes.

Fission fragment mass distributions for 19F+184W have been measured at beam energies in the range of 85 - 125 MeV. Analysis of mass distribution width indicates that the system proceeds towards the formation of compound nucleus. No signature of quasifission is observed in this reaction. These results strengthen the conclusions of our earlier works revealing the stabilizing effect of the Z = 82 shell closure against fission.

Evaporation residue (ER) excitation function in the complete fusion of 16O with 194Pt is measured around the Coulomb barrier using gas-filled mode of the HYbrid Recoil mass Analyser (HYRA) at the Inter University Accelerator Centre (IUAC), New Delhi. Measured ER excitation function is compared with statistical model calculation. Nuclear dissipation strength β = 1.5 is required to explain the experimental data at higher excitation energies.

The role of nucleon transfer channel coupling on the sub-barrier fusion excitation function has been elusive. Many studies have attributed a significant sub-barrier fusion cross-section enhancement over one-dimensional barrier penetration model (1d-BPM) calculation to nucleon transfer couplings. However, several systems exhibit no such enhancement besides having positive Q-value nucleon transfer channels.The objective is to delve into the role of coupling to various internal degrees of freedom on the fusion excitation functions in interactions of 19 F with 64 , 68 Zn. Fusion cross-section measurements are performed at energies ∼ 20 % above to ∼ 15 % below the Coulomb barrier using Heavy Ion Reaction Analyzer (HIRA) at Inter-University Accelerator Center (IUAC), New Delhi. Coupled-channel (CC) calculations, including coupling to vibrational states of 64 , 68 Zn, rotational states of 19 F, and nucleon transfer channels are performed. Cross-sections for various transfer channels are calculated to speculate their coupling effects on the fusion excitation functions. The results are compared on a reduced scale with neighboring systems involving 19 F and 18 O as the projectile. The sub-barrier fusion cross-sections of 19 F + 64 , 68 Zn systems are enhanced by orders of magnitude compared to the corresponding 1d-BPM calculations. CC calculations performed with CCFULL, including coupling to collective excitations of reactants and pair transfer channel, failed to reproduce the experimental fusion cross-sections. GRAZING calculations show large one nucleon transfer cross-sections relative to other channels for the two systems. CCDEF calculation show that inclusion of coupling to one proton transfer channel is necessary to reproduce the experimental data for both systems. [ABSTRACT FROM AUTHOR]