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Elastic scattering angular distributions have been measured for 7 Li+ 92 , 100 Mo systems in the bombarding energy range of 0.85 to almost two times the Coulomb barrier. The measured elastic scattering angular distributions are fitted using optical model to investigate energy dependence of the real and imaginary strength parameters with phenomenological Woods-Saxon and double folding S a ~ o Paulo potentials. Both interaction potential models simulate similar patterns to energy dependence sustaining the same consequence of breakup threshold anomaly. The results of Continuum Discretized Coupled Channels (CDCC) Calculations with inclusion of the breakup coupling of the projectile compares experimental elastic scattering angular distribution better for the 7 Li+ 92 , 100 Mo systems rather than excluding breakup coupling. A systematic behaviour of total reaction cross section on target and projectile dependency has been investigated by including a wide range of target mass and tightly to weakly bound projectiles. A comparative study on obtained breakup and reaction cross sections has also been carried out for 7 Li+ 92 , 100 Mo systems. [ABSTRACT FROM AUTHOR]

Experimental fission cross-sections are reported for the 19F + 194,196,198Pt reactions populating an isotopic chain of compound nuclei comprising both closed and non-closed shell nuclei. The fission cross-sections are obtained at near and above Coulomb barrier energies by measuring fission fragment angular distributions. The present work aims to estimate nuclear dissipation and find its isotopic and shell closure dependence from statistical model (SM) analysis of experimental data. Pre-scission neutron multiplicity data for the same systems is also included in the SM analysis. An updated version of SM is used in the present analysis, which includes shell corrections in level density and fission barrier as well as the effect of collective enhancement of level density and orientation effect of the compound nucleus along the symmetry axis. An isotopic dependence of the dissipation strength fitting the fission excitation functions is observed. The pre-scission neutron multiplicity, however, is underestimated by the SM. [ABSTRACT FROM AUTHOR]

Abstract: The characteristics and performance of a new detector system developed for the study of low energy heavy ion binary reactions using the kinematic coincidence technique are presented. The detector system has been developed to carry out experiments such as multi-nucleon transfer reactions using the General Purpose Scattering Chamber (GPSC) facility at IUAC [1,2]. The detector system consists of a pair of two-dimensional position sensitive multi wire proportional counter (MWPC) and a gas ionization chamber. Both MWPC have an active area of 5×5cm2, and provide position signals in horizontal (X) and vertical (Y) plane, and timing signal for time of flight measurements. The main design feature of MWPC is the reduced wire pitch of 0.025in. (0.635mm) in all electrodes, giving uniform field and faster charge collection, and usage of diameter in anode frame which gives higher gains. The position resolution of the detectors was determined to be 0.45mm FWHM and time resolution was estimated to be 400ps FWHM. The detector could handle heavy ion count rates exceeding 100kHz without any break down. The timing and position signals of the detectors are used for kinematic coincidence measurements and subsequent extraction of their mass and angular distributions. The ionization chamber has a conventional transverse field geometry with segmented anode providing multiple signals for nuclear charge (Z) identification. This article describes systematic study of these detectors in terms of efficiency, count rate handling capability, time, position and energy resolution. [Copyright &y& Elsevier]

Background: Complete fusion between two massive nuclei after capture inside the potential barrier is inhibited by competing fission-like processes. The target-projectile composite system may reseparate after capture without proceeding towards formation of the compound nucleus (CN), which is equilibrated in all degrees of freedom. The nature of these non-CN fission (NCNF) processes and factors that affect them are not completely known yet. Purpose: The nuclear mass regions from where NCNF processes begin to manifest themselves are not clearly demarcated. This work aims to study the onset of NCNF, if any, in the mass region ~200. Methods: Fission fragment (FF) mass and angular distribution (MAD) and pre-scission and post-scission neutron multiplicities were measured for the reaction 19F + 184W at a laboratory energy (Elab) range of 84-125 MeV. The measurements were carried out using two multiwire proportional counters (MWPC) to detect the FFs in coincidence and four neutron detectors to measure neutron time of flight (TOF). Statistical model (SM) calculation was performed. Results: No significant mass-angle correlation was observed in the MAD plots. Extracted mass ratio distributions were single-peaked and of Gaussian shape. Measured pre-scission neutron multiplicity values indicated dissipative nature of CN decay for this reaction. Conclusions: No clear signatures of NCNF were observed in the studied reaction, indicating that the target-projectile composite system predominantly proceeds towards formation of the CN after capture. [ABSTRACT FROM AUTHOR]

Background: The l2C(6Li,d) reaction has been used as an indirect method to calculate the astrophysical S factor for the l2C(α,γ) reaction at Gamow energy (300 keV). Purpose: The 12C(6Li,d) reaction is usually interpreted in terms of direct transfer. In this work we investigate the reaction mechanism and determine the effects of breakup on transfer and therefore on the extracted spectroscopic amplitudes. Method: The deuteron angular distributions for the l2C(6Li,d)l6O*has been measured at 20 MeV, populating discrete states of 160. continuum discretized coupled channel-coupled reaction channel (CDCC-CRC) calculations have been used to analyze the data. Results: Results show a new reaction mechanism, where transfer occurs after the breakup of the loosely bound 6Li in the population of some bound states of 160. A comparison of the CDCC-CRC calculations with respect to the measured data were used to determine the a spectroscopic amplitudes and factors for the different states of 160. Using the spectroscopic amplitudes obtained in this work, the E2 S factor for the nC(a,y) reaction has been calculated in the framework of a two-body potential model and compared to measurements. Conclusions: The present study very clearly shows that the breakup and transfer coupling effects are strong in the 12C(6Li,d) reaction. The present work extracts, in the framework of a coupled reaction channel theory, the spectroscopic amplitudes of the bound and unbound states of l6O. All previous analysis and new measurements should therefore be reexamined from this viewpoint to extract the astrophysical observables correctly. [ABSTRACT FROM AUTHOR]

Abstract: Fission fragment angular distributions have been measured for 16O+ 194Pt reaction forming the compound system 210Rn, in the laboratory energy range from 79 to 90 MeV. The measured fission fragment anisotropies as a function of are compared with the predictions of standard saddle point statistical model (sspm). Anisotropies calculated using the average excitation energy and angular momentum values could not reasonably fit the experimental data. Statistical model calculations were performed using the pace with modified fission barrier and level density parameters. Fission probability, evaporation residue cross section and neutron multiplicity were simultaneously used to fix the statistical parameters. Model calculations incorporating the chance nature of fission decay and scaled values of the rotating finite range model (RFRM) moment of inertia could reasonably fit the fragment angular anisotropies. [Copyright &y& Elsevier]

Measurements of angular distributions for one- and two-proton stripping reactions for 28Si + 90'94Zr systems were performed at 120 MeV. The experiment was carried out with the 28Si beam at Inter University Accelerator Center, New Delhi. The theoretical calculations were performed using the quantum mechanical coupled reaction channels code FRESCO. The distorted wave Born approximation calculations reproduced the experimental angular distributions for the one-proton transfer channel for both the systems reasonably well but failed for the two-proton transfer channel. Coupled channels calculations including various intermediate states (involving target and projectile inelastic excitations before and/or after transfer) along with the sequential transfer were able to reproduce the two-proton transfer angular distributions for both the systems reasonably well. It seems that at an energy above the Coulomb barrier, there is significant contribution of the indirect multistep and sequential transfer to the two-proton stripping reaction. [ABSTRACT FROM AUTHOR]

Background: Complete fusion of two nuclei leading to formation of a heavy compound nucleus (CN) is known to be hindered by various fission-like processes, in which the composite system reseparates after capture of the target and the projectile inside the potential barrier. As a consequence of these non-CN fission (NCNF) processes, fusion probability (PCN) starts deviating from unity. Despite substantial progress in understanding, the onset and the experimental signatures of NCNF and the degree of its influence on fusion have not yet been unambiguously identified. Purpose: This work aims to investigate the presence of NCNF, if any, in pre-actinide nuclei by systematic study of fission angular anisotropies and fission cross sections (sfis) in a number of nuclear reactions carried out at and above the Coulomb barrier (VB). Method: Fission fragment angular distributions were measured for six 28Si-induced reactions involving isotopically enriched targets of 169Tm,176Yb,175Lu,180Hf,181Ta, and 182W leading to probable formation of CN in the pre-actinide region, at a laboratory energy (Elab) range of 129-146 MeV. Measurements were performed with large angular coverage (θlab=41∘-170∘) in which fission fragments (FFs) were detected by nine hybrid telescope (E−ΔE) detectors. Extracted fission angular anisotropies and σfis were compared with statistical model (SM) predictions. Results: Barring two reactions involving targets with large non-zero ground state spin (J), viz., 175Lu... and 181Ta..., experimental fission angular anisotropies were found to be higher in comparison with predictions of the statistical saddle point model (SSPM), at Ec.m. near VB. Comparison of present results with those from neighboring systems revealed that experimental anisotropies increasingly deviated from SSPM predictions as one moved from pre-actinide to actinide nuclei. For reactions involving targets with large nonzero J, this deviation was subdued. Comparison between measured sfis and predictions of SM indicated the presence of NCNF in at least four systems, when shell effects, both in the level density and the fission barrier, were included in the calculation. Conclusions: Systematic SM analysis of measured fission angular anisotropies and σfis confirmed the onset of NCNF in pre-actinide nuclei. Discrepancies between results about the degree of its influence on complete fusion, as deduced from various experimental probes, remain challenges to be solved. Complete measurement of all signatures of NCNF for many systems and preferably a dynamical description of the collisions between projectile and target nuclei are warranted for a deeper understanding. [ABSTRACT FROM AUTHOR]

Abstract: Fission fragment mass angle correlation and mass ratio distributions have been measured for 16O + 194Pt reaction forming the composite system 210Rn in the energy range 75 MeV to 102 MeV in laboratory frame. No mass angle correlation was observed and the mass ratio distributions were compared with theoretical calculations assuming compound nucleus formation. No evidence of quasi-fission process is observed in the reaction. [Copyright &y& Elsevier]