Nuclear dissipation at high excitation energy and angular momenta in reaction forming Np227

Abstract

Neutron multiplicity excitation function has been measured for the $^{30}\mathrm{Si}+^{197}\mathrm{Au}$ reaction populating the $^{227}\mathrm{Np}$ 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 ${\ensuremath{\nu}}_{\mathrm{pre}}$ 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.