For the first time, we have simultaneously measured fusion and quasielastic excitation functions for an intermediate mass system for angular momentum, ℓ∼ 0 using a recoil mass spectrometer. We have extracted barrier distributions using three different sets of data recorded simultaneously for the reaction ^16 O+ ^142 Ce: (a) fusion excitation function from measurement of evaporation residues at angle, θ _lab = 0^∘ , (b) quasielastic excitation function at center of mass scattering angle, θ _c.m. = π via measurement of scattered target-like ions at θ _lab = 0^∘ and (c) quasielastic excitation functions from measurement of scattered projectile-like ions at two large angles. We show that the four barrier distributions yield nearly identical results with a single peak. However, the centroids of the barriers extracted from quasielastic data at large angles are lower by ∼ 600 keV compared to the same of the barriers extracted from fusion and quasielastic data for ℓ∼ 0 . This is the first experimental verification of the validity of scaling property with respect to ℓ and iso-centrifugal approximation in extracting fusion barrier distribution from quasielastic scattering. This work also points to the importance of extracting barrier distribution from quasielastic measurements at θ _c.m. = π for systems for which measuring fusion excitation function with high precision is not feasible.

Evaporation residue cross-sections have been measured for 19F+142,150Nd reactions in the energy range 15% below to 30% above the Coulomb barrier at the Inter-University Accelerator Centre, New Delhi, using the heavy ion reaction analyzer (HIRA). The measured fusion excitation functions were compared with the calculations using the coupled channels code CCFULL, including different couplings of the reactants. Fusion barrier distribution is extracted from the measured fusion cross-sections. Significant enhancement in fusion cross-section is observed in both reactions at sub-barrier energies. Enhancement is larger for the 19F+150Nd reaction compared to the 19F+142Nd reaction. The coupling of target excitations alone could not reproduce the observed fusion enhancement in both systems at sub-barrier energies. Calculations have been performed treating 19F as a vibrational as well as a rotational nucleus. Coupled channels calculations assuming 19F as a rotor reproduce the fusion excitation function reasonably well in both systems. However, these calculations do not require the coupling of transfer channels despite the presence of positive Q-value transfer channels in both systems. This warrants transfer cross-section measurements in both systems.

Evaporation residue (ER) cross-sections were measured for 30Si+142Ce reaction at laboratory energies in the range of 105 - 132 MeV using the HYbrid Recoil mass Analyzer (HYRA) at IUAC, New Delhi. The transmission efficiency of the HYRA was estimated using the calibration reaction 28Si+142Ce. Sub-barrier fusion enhancement was observed when compared with the one-dimensional barrier penetration model predictions for the present system. To explore the phenomena responsible for sub-barrier fusion enhancement, coupled-channels calculations were performed using the CCFULL code. The effect of couplings and the role of positive Q-value neutron transfer (PQNT) channels on sub-barrier fusion cross-sections were investigated. Coupled-channels calculations were able to reproduce the data by including the coupling in both projectile and target nucleus along with two neutron-transfer channels having positive Q-value. The measured ER cross-sections were compared with the nearby systems to explore the role of deformation of the colliding nuclei.

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 O-16+Cd-116 and O-16+Ce-142. We also present comparisons of the same with the data for existing symmetric systems having nearly similar values of the zeta 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.

In heavy-ion collision experiments, the fusion cross section in the sub-barrier energy region is found to be enhanced by several orders of magnitude in comparison to the prediction of the one-dimensional barrier penetration model (1D-BPM) that involves the quantum mechanical tunneling effect during fusion. So far, the coupling-aided tunneling due to participating nuclei’s intrinsic degrees of freedom continues to be identified as an accountable factor. We intend to probe the role of structural properties and low-lying inelastic excitations of the colliding nuclei in driving the fusion phenomenon for energies in the near and sub-barrier regions. In the study, the fusion excitation function has been measured for ^30Si+^140Ce reaction for energies ≈ 11

Evaporation Residue (ER) cross-sections and ER-gated $\gamma$-ray fold distributions are measured for the $^{32}$S + $^{154}$Sm nuclear reaction above the Coulomb barrier at six different beam energies from 148 to 191 MeV. $\gamma$-ray multiplicities and spin distributions are extracted from the ER-gated fold distributions. The ER cross-sections measured in the present work are found to be much higher than what was reported in a previous work using a very different target-projectile ($^{48}$Ti + $^{138}$Ba) combination, leading to the same compound nucleus $^{186}$Pt, with much less mass asymmetry in the entrance channel than the present reaction. This clearly demonstrates the effect of the entrance channel on ER production cross-section. The ER cross-sections measured in the present work are compared with the results of both the statistical model calculations and the dynamical model calculations. Statistical model calculations have been performed to generate a range of parameter space for both the barrier height and Kramers' viscosity parameter over which the ER cross-section data can be reproduced. The calculations performed using the dinuclear system (DNS) model reproduce the data considering both complete and incomplete fusion processes. DNS calculations indicate the need for the inclusion of incomplete fusion channel at higher energies to reproduce the ER cross-sections.

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 Si-28+Gd-158 as compared to Si-30+Ce-140 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.

The evaporation residue (ER) cross sections for the reaction F19+187Re→206Po⁎ are measured, in the excitation energy range of 86.1 to 118.4 MeV. The measured cross sections are compared with that of 30Si + 176Yb reaction populating the same compound nucleus. Theoretical calculations are performed using the coupled - channels calculations for the capture cross sections and statistical model calculations for the ER cross sections. The dependence of quasi fission on entrance channel parameters such as charge product (Z1Z2), mass asymmetry (α), target deformation (β2) and effective fissility (χeff) are studied.

The dynamics of heavy ion-induced reactions play a critical role in forming super heavy elements (SHE), and one clear signature of the SHE formation is the evaporation residue (ER). In our pursuit of SHE, we present the heaviest element populated in India for ER cross-section measurements. These are the first-ever measurements of the Evaporation Residue (ER) cross-sections for the nuclear reactions between $^{32}$S and $^{208}$Pb. These measurements were conducted above the Coulomb barrier at four distinct beam energies in the laboratory frame, ranging from 176 to 191 MeV at the pelletron Linac facility at the Inter-University Accelerator Centre (IUAC), New Delhi. The Hybrid Recoil Mass Analyzer (HYRA) in a gas-filled mode was employed for these experiments. The obtained range of ER cross-sections enriches our knowledge and helps advance the field of heavy ion-induced reactions, especially in the context of super heavy element formation.

The challenging task in heavy-ion collisions is unambiguously identifying the true fusion events in the deep sub-barrier region. Considering the primary challenge, we have measured fusion excitation functions for Si-28+ Gd-158 reaction at energies above to deep sub-barrier region to decipher the role of multineutron transfer with positive Q value and fusion hindrance in an asymmetric system. A comparison has been made with our previous measurement for Si-30+ Gd-156 system where only one transfer channel with Q > 0 exists and populates the same compound nucleus Pt-186 *. The enhancement in fusion cross sections is observed on a reduced scale in the Si-28+ Gd-158 reaction over Si-30+ Gd-156 system at sub-barrier energies. The measured fusion data and extracted barrier distribution have been analyzed within the framework of coupled-channels (CC) programs, CCFULL and empirical channel coupling. Coupling to rotational excitations in projectile and target along with up to 2n transfer channel with positive Q value is found to be promising to explain the fusion excitation functions except for the lowest energy point. However, the influence of more than two neutrons transfer is insignificant in Si-28+ Gd-158 system. At the lowest energy (approximate to 14% down the Coulomb barrier), a deviation from standard CC has been found, which may indicate the threshold for fusion hindrance, but additional lower-energy data are needed to prove this. The experimental threshold energy (E-S) for fusion hindrance is in good agreement with the empirical formula, and it is consistent with the observed pattern of E-S as a function of the entrance channel parameter (zeta) for other nearly symmetric and asymmetric systems.

The phenomenon of enhanced fusion cross-section as compared to the theoretical predictions of 1-D BPM has been extensively studied over the past few decades. However, the unambiguous role of neutron transfer channels on the sub-barrier fusion enhancement is still elusive in most cases. Fusion cross-section measurements ≈ 15% below and above the Coulomb barrier were performed to elucidate the mechanisms responsible for the experimentally observed sub-barrier fusion enhancement. Coupled-channels calculations using CCFULL were used to decipher the reaction dynamics. CC calculations explained the fusion excitation function for 28Si + 116,120Sn systems after the inclusion of inelastic excitations along with a pair transfer. However, the observed behavior for the 28Si + 124Sn system could not be explained. The fusion barrier distribution has been extracted from the experimental data to unveil the various channels coupled in the concerned rection. A single uncoupled barrier was transformed into a distribution of barriers depicting the presence of different channels coupled in the reaction. The results indicate a significant effect from multi-neutron transfer channels on the fusion dynamics.

Coupled reaction channel approach has been quite successful in describing the mechanism of multi-nucleon transfer in heavy ion-induced reactions. However, considerable ambiguities exist in the choice of potential parameters and the states of participating nuclides that should be coupled for a given reaction channel. Here we report simultaneous analysis of both angular distributions and excitation functions for one- and two-nucleon transfer in the systems Si-28+Zr-90,Zr-94 within the coupled reaction channel formalism. Spectroscopic amplitudes are obtained from the literature and large-scale shell model calculations. The uncertainties in the cross sections, introduced by the choice of effective interactions in shell model, are also investigated. While one-nucleon transfer in the system Si-28+Zr-94 have been well reproduced by inclusion of the ground and the first excited states of projectile-likes in the exit channel, more states of the same are to be coupled for the system Si-28+Zr-90. Observed bell-shaped angular distribution of one-proton stripping channel in( 28)Si+Zr-94 is found to be caused by a large contribution of direct transfer from the ground and the first excited states of projectile-likes. In contrast, a flat angular distribution of one-proton stripping channel in Si-28+Zr-90 appears to have been caused by a large number of indirect transitions. For two-nucleon transfer, both one-step and two-step processes have been considered. Reasonable reproduction of measured cross sections has been achieved by application of the extreme cluster model for the transfer of a pair of nucleons. No arbitrary scaling of the theoretical results has been necessary and only a minor variation of the binding radius has been allowed in our calculations. More such studies are warranted for mitigating the ambiguities in coupled reaction channel description of multi-nucleon transfer.

Fabrication and characterization of thin target films of  116Cd by physical vapour deposition technique are reported. The target films were used in the study of nuclear fusion dynamics near the Coulomb barrier with a beam of  16O. Because of the low melting point of cadmium and its re-evaporation after deposition, coupled with availability of a very small quantity of isotopically enriched material, an unconventional method was employed to fabricate the targets. The prepared target films were characterized using Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), X-ray Diffractometry (XRD) and Rutherford Back-scattering Spectroscopy (RBS) to obtain their surface morphology, elemental composition, chemical composition and thickness, respectively. Thickness of the enriched target films were in the range of 20 –50 μg/cm2. Isotopic composition of one of the target films was ascertained in an in-beam experiment using a recoil mass spectrometer. It was observed that abundance of  116Cd in the fabricated target film was significantly lower than the value quoted by the supplier of the source material.

We report the first direct measurement of differential transfer cross sections using a Recoil Mass Spectrometer. Absolute differential 1 p - and 2 p -stripping cross sections at θ _c.m.=180^∘ have been determined for the system ^16 O+ ^142 Ce by detecting the heavier target-like ions at the focal plane of the Heavy Ion Reaction Analyzer. Focal plane spectra have been compared with the results of a semi-microscopic Monte-Carlo simulation to unambiguously identify the transfer channels. The methodology adopted in this work can be applied to measure multi-nucleon transfer cross sections using other similar recoil separators. The experimental excitation functions for the reactions ^142Ce(^16O,^15N)^143Pr and ^142Ce(^16O,^14C)^144Nd have been compared with coupled reaction channels calculations. Shell model calculations have been performed to extract spectroscopic information for the target-like nuclei. An excellent matching between measurement and theory has been obtained for 1 p -stripping. For 2 p -stripping, cluster transfer of two protons has been found to have dominant contribution. Measured transfer probabilities for 1 p - and 2 p -stripping channels have been compared with Time-Dependent Hartree–Fock calculations. Proton stripping channels are found to be more favourable compared to neutron pick-up channels. However, the theory overpredicts the measurement hinting at the need for extended approaches with explicit treatment of pairing correlations in the calculations.

Coupled reaction channel approach has been quite successful in describing the mechanism of multi-nucleon transfer in heavy ion-induced reactions. However, considerable ambiguities exist in the choice of potential parameters and the states of participating nuclides that should be coupled for a given reaction channel. Here we report simultaneous analysis of both angular distributions and excitation functions for one- and two-nucleon transfer in the systems ^28 Si+ ^90,94 Zr within the coupled reaction channel formalism. Spectroscopic amplitudes are obtained from the literature and large-scale shell model calculations. The uncertainties in the cross sections, introduced by the choice of effective interactions in shell model, are also investigated. While one-nucleon transfer in the system ^28 Si+ ^94 Zr have been well reproduced by inclusion of the ground and the first excited states of projectile-likes in the exit channel, more states of the same are to be coupled for the system ^28 Si+ ^90 Zr. Observed bell-shaped angular distribution of one-proton stripping channel in ^28 Si+ ^94 Zr is found to be caused by a large contribution of direct transfer from the ground and the first excited states of projectile-likes. In contrast, a flat angular distribution of one-proton stripping channel in ^28 Si+ ^90 Zr appears to have been caused by a large number of indirect transitions. For two-nucleon transfer, both one-step and two-step processes have been considered. Reasonable reproduction of measured cross sections has been achieved by application of the extreme cluster model for the transfer of a pair of nucleons. No arbitrary scaling of the theoretical results has been necessary and only a minor variation of the binding radius has been allowed in our calculations. More such studies are warranted for mitigating the ambiguities in coupled reaction channel description of multi-nucleon transfer.

Distribution of fusion barriers reveals the effect of structure of the collision partners on the dynamics of fusion between two heavy ions. Experimental barrier distribution can be extracted from precisely measured fusion excitation function. Quasielastic excitation function is related to fusion excitation function by conservation of incident flux. Hence, barrier distribution can also be extracted from quasielastic excitation function, which is usually measured at large angles, by detecting the back-scattered projectile-like ions. However, the reflectance coefficient is exactly complementary to the transmittance coefficient at θ c.m. = 180°, which corresponds to orbital angular momentum, ℓ = 0. We report here extraction of fusion barrier distribution for 16O+142 Ce from measurement of quasielastic scattering at θ c.m. = 180°, by detecting the target-like ions in the forward angles using a recoil mass spectrometer. Quasielastic excitation functions were also measured by detecting the projectile-like ions at two large angles. Barrier distributions extracted from both fusion and quasielastic measurements were found to be nearly identical. This work, thus, provided the first experimental verification of validity of the scaling property and the iso-centrifugal approximation in extracting barrier distribution from quasielastic excitation functions measured at large angles.

Evaporation residue (ER) cross sections are measured for the reaction $^{30}\mathrm{Si}+^{176}\mathrm{Yb}$, which forms the compound nucleus $^{206}\mathrm{Po}^{*}$, over the excitation energy range from 47.68 to 113.73 MeV. Dependence of noncompound nuclear reaction on entrance channel parameters such as charge product (${Z}_{1}{Z}_{2}$), mass asymmetry ($\ensuremath{\alpha}$), deformation (${\ensuremath{\beta}}_{2}$) of the target, and isospin asymmetry ($\mathrm{\ensuremath{\Delta}}\frac{N}{Z}$) is explored. To analyze the experimental data the coupled-channels and the statistical model calculations are used. The measured ER cross sections are compared with the system,$^{12}\mathrm{C}+^{194}\mathrm{Pt}$ forming the same compound nucleus and also with $^{28}\mathrm{Si}+^{176}\mathrm{Yb}$, forming $^{204}\mathrm{Po}^{*}$ in the neighborhood. Observed suppression in the evaporation residue cross sections at higher energies may be attributed to the presence of the noncompound nuclear process.