Projectile - Mass asymmetry systematics for low energy incomplete fusion

¹ Department of Physics, Indian Institute of Technology Ropar, Rupnagar, PB - 140 001, India
² NP-Division, Inter-University Accelerator Centre, New Delhi - 110 067, India
³ Acc. Lab., Department of Physics, A. M. University, Aligarh, UP - 202 002, India
⁴ Physics Department, S. V. College, Aligarh, UP - 202 001, India

^a e-mail: pps@iitrpr.ac.in

Published online: 2 June 2015

Abstract

In the present work, low energy incomplete fusion (ICF) in which only a part of projectile fuses with target nucleus has been investigated in terms of various entrance channel parameters. The ICF strength function has been extracted from the analysis of experimental excitation functions (EFs) measured for different projectile-target combinations from near- to well above- barrier energies in ¹²C,¹⁶O(from 1.02V_b to 1.64V_b)+¹⁶⁹Tm systems. Experimental EFs have been analysed in the framework statistical model code PACE4 based on the idea of equilibrated compound nucleus decay. It has been found that the value of ICF fraction (F_ICF) increases with incident projectile energy. A substantial fraction of ICF (F_ICF ≈ 7 %) has been accounted even at energy as low as ≈ 7.5% above the barrier (at relative velocity ν_rel ≈0.027) in ¹²C+¹⁶⁹Tm system, and F_ICF ≈ 10 % at ν_rel ≈0.014 in ¹⁶O+¹⁶⁹Tm system. The probability of ICF is discussed in light of the Morgenstern’s mass-asymmetry systematics. The value of F_ICF for ¹⁶O+¹⁶⁹Tm systems is found to be 18.3 % higher than that observed for ¹²C+¹⁶⁹Tm systems. Present results together with the re-analysis of existing data for nearby systems conclusively demonstrate strong competition of ICF with CF even at slightly above barrier energies, and strong projectile dependence that seems to supplement the Morgenstern’s systematics.