PHYSICAL REVIEW C 98, 034601 (2018) Systematic study of 192,202,206,210 Po compound nuclei using neutron multiplicity as a probe Ruchi Mahajan, * B. R. Behera, † Meenu Thakur, Gurpreet Kaur, Priya Sharma, Kushal Kapoor, and A. Kumar Department of Physics, Panjab University, Chandigarh 160014, India P. Sugathan, A. Jhingan, A. Chatterjee, N. Saneesh, A. Yadav, and R. Dubey Inter University Accelerator Centre, Aruna Asaf Ali Marg, New Delhi 110067, India Neeraj Kumar Department of Physics and Astrophysics, University of Delhi 110067, India Hardev Singh Department of Physics, Kurukshetra University, Kurukshetra 136119, India A. Saxena Nuclear Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India Santanu Pal ‡ CS-6/1, Golf Green, Kolkata 700095, India (Received 23 September 2017; revised manuscript received 15 January 2018; published 4 September 2018) In the present work we have measured pre- and post-scission neutron multiplicities (M pre and M post ) from two compound nuclei, namely 192,202 Po populated by 48 Ti + 144,154 Sm systems at 72 MeV of excitation energy using the National Array of Neutron Detectors (NAND) facility at IUAC, New Delhi. Statistical model analysis has been performed for 48 Ti + 144,154 Sm along with already existing data for 12 C + 194 Pt and 18 O + 192 Os covering compound nuclei of Po ( 192,202,206,210 Po) with neutron number N C = 108, 118, 122, and 126 respectively. Variation of experimental M pre with N/Z of the compound nucleus does not show any special feature at neutron shell closure (N C = 126) at compound nucleus excitation energy around 72 MeV considered here. In particular, it is found that dissipation alone is unable to reproduce the experimental M pre for 192 Po, and the role of entrance channel dynamics should be considered in future works. DOI: 10.1103/PhysRevC.98.034601 I. INTRODUCTION Fusion-fission of heavy nuclei is a complex dynamical process in which many degrees of freedom are involved. Though many aspects of this process have been investigated both qualitatively and quantitatively in the past, it is yet to be fully understood [1]. Following the capture of a projectile by a target nucleus, a compound nucleus (CN) is usually formed after complete equilibration in all the degrees of freedom. Subsequently the CN de-excites by competing processes of evaporation of light particles and photons, and fission. Some- times the dinuclear system may segregate prematurely before forming a fully equilibrated CN. Such events with various de- grees of equilibration appear between deep-inelastic collisions (DICs) and complete fusion [2]. In DIC, the entrance channel mass asymmetry is approximately preserved but there can be large dissipation of kinetic energy and angular momentum. CN * ruchimahajan4@gmail.com † Corresponding author: bivash@pu.ac.in ‡ Formerly with VECC, Kolkata. formation, in contrast, is characterized by equilibration of all degrees of freedom, and hence complete loss of identity of the entrance channel. Intermediate between DIC and CN fission, quasifission (QF) has full energy dissipation but incomplete drift toward the energetically favored mass-symmetric config- uration [3–12]. It has been shown earlier from analyses of a large vol- ume of experimental data from fusion-fission reactions that the multiplicities of different types of evaporation species are larger compared to the standard statistical model (SM) predictions [13,14]. This excess yield of particles and γ rays from heavy compound systems suggests a slowing down of the fission process as given by the transition-state model of fission [15]. The slowing down of the fission process or fission hindrance can be described by incorporating nuclear dissipation and transient effects allowing for the buildup of the fission flux [16–18]. Phenomenologically, it was suggested by Blocki et al. [19] that nuclear dissipation at moderate excitation energies is one-body in nature and arises out of the collisions of the nucleons with the moving nuclear surface (wall formula) and also due to the exchange of nucleons between the two lobes when the nucleus has a dinuclear shape (window formula). 2469-9985/2018/98(3)/034601(10) 034601-1 ©2018 American Physical Society