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Measurements of cross sections of evaporation residue (ER) and spin distributions of heavy nuclei, produced via compound nuclear fusion-evaporation reactions, provide crucial information about the dynamics of nuclear fission and the survival probability of the system against fission. Such measurements help in probing the evolution of the compound system from equilibrium to the saddle and the underlying role of nuclear dissipation in hindering fission. The purpose of the present measurements is to understand the survival probability of the 224Th* compound nucleus against fission and its dependence on angular momentum. Measurements of the ER cross sections and spin distributions have been carried out for the 16O+208Pb and 18O+206Pb reactions which form the same 224Th* compound nucleus. The two reactions have been carried out at laboratory energies ranging from 87 MeV to 122.6 MeV and 85.7 MeV to 121.4 MeV, respectively. The measurements have been performed at Inter University Accelerator Centre, New Delhi using the Hybrid Recoil mass Analyzer in gas-filled mode, coupled with the 4π spin spectrometer of Tata Institute of Fundamental Research. The reduced ER cross sections (σER/πRB²) for both systems are comparable at low excitation energies while at higher excitation energies the 18O+206Pb system shows nearly 50% higher values. However, the 18O+206Pb system shows lower mean γ ray multiplicity (and hence lower mean angular momentum) at all excitation energies which is a surprising result. [ABSTRACT FROM AUTHOR]

Evaporation residue cross sections for the 16O + 203,205Tl reactions were measured at laboratory beam energies in the range of 82-113 MeV using a gas-filled separator. Transmission efficiency of the separator was estimated using a calibration reaction 16O + 197Au and by simulating the evaporation residues angular distributions. Statistical model calculations were performed for both the measured systems. These calculations overestimate the experimental evaporation residue cross sections. This could be attributed to the presence of noncompound nuclear fission. An estimation of noncompound nuclear fission contribution was carried out. Comparison with neighboring systems shows that a slight change in the entrance channel or the compound nucleus properties makes a large difference in evaporation residue cross sections. [ABSTRACT FROM AUTHOR]

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]