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Neutron multiplicity excitation function has been measured for the 30Si+197Au reaction populating the 227Np compound nucleus at excitation energies in the range 44.1-78.8 MeV using the National Array of Neutron Detector facility of Inter University Accelerator Centre, New Delhi. Measured pre-scission neutron multiplicity values are analyzed using a statistical model incorporating Krammer's fission width due to the dissipative drag in nuclear fission, shell corrections in fission barrier and level density, collective enhancement of level density, and K-orientation effect. The present work demonstrates that a strong fission hindrance is essential to reproduce the experimental pre-scission neutrons, whereas the temperature dependent dissipation coefficient as observed in a few recent measurements is not required to reproduce the experimental νpre data. No substantial effect of collective enhancement of nuclear level density and tilting away effect of compound nucleus spin on neutron emission prior to the scission configuration was observed unlike fission of preactinides. [ABSTRACT FROM AUTHOR]

Background: A significant research effort is currently aimed at understanding the synthesis of heavy elements. For this purpose, heavy ion induced fusion reactions are used and various experimental observations have indicated the influence of shell and deformation effects in the compound nucleus (CN) formation. There is a need to understand these two effects. Purpose: To investigate the effect of proton shell closure and deformation through the comparison of evaporation residue (ER) cross sections for the systems involving heavy compound nuclei around the ZCN=82 region. Methods: A systematic study of ER cross-section measurements was carried out for the 48Ti+142,150Nd, 144Sm systems in the energy range of 140-205MeV. The measurement has been performed using the gas-filled mode of the hybrid recoil mass analyzer present at the Inter University Accelerator Centre (IUAC), New Delhi. Theoretical calculations based on a statistical model were carried out incorporating an adjustable barrier scaling factor to fit the experimental ER cross section. Coupled-channel calculations were also performed using the ccfull code to obtain the spin distribution of the CN, which was used as an input in the calculations. Results: Experimental ER cross sections for 48Ti+142,150Nd were found to be considerably smaller than the statistical model predictions whereas experimental and statistical model predictions for 48Ti+144Sm were of comparable magnitudes. Conclusion: Though comparison of experimental ER cross sections with statistical model predictions indicate considerable non-compound-nuclear processes for 48Ti+142,150Nd reactions, no such evidence is found for the 48Ti+144Sm system. Further investigations are required to understand the difference in fusion probabilities of 48Ti+142Nd and 48Ti+144Sm systems. [ABSTRACT FROM AUTHOR]

Background: Couplings with various reaction channels are known to enhance sub-barrier fusion cross sections by several orders in magnitude. However, a few open questions still remain. For example, the influence of higher order static deformations on sub-barrier fusion cross sections is yet to be comprehensively understood. Purpose: We study the role of hexadecapole nuclear deformation effect on sub-barrier fusion cross sections. Also, this work aims to extract hexadecapole deformation (β4) in nuclei in the lanthanide region. Method: The evaporation residue (ER) excitation functions for 16O+174,176Yb were measured at laboratory beam energies (Elab) in the range of 64.6-103.6 MeV. Measurements were carried out by employing the recoil mass spectrometer Heavy Ion Reaction Analyzer (HIRA) at IUAC, New Delhi. Fusion barrier distributions (BDs) were extracted from data. Results from the experiment were subjected to coupled-channels analysis, in which β4 was varied as a free parameter. Results: Experimental fusion cross sections at energies below the barrier expectedly showed strong enhancement compared to the predictions from the one-dimensional barrier penetration model. Data were satisfactorily reproduced after inclusion of negative β4 for both the targets in the coupled-channels calculation. Conclusions: The significant role of hexadecapole deformation was observed in the sub-barrier fusion of 16O+174,176Yb. The proposed value of β4 reproduced the measured fusion excitation function reasonably well. The BDs from these data were also extracted but no definitive conclusions could be drawn from them. [ABSTRACT FROM AUTHOR]