Effect of projectile breakup on fission-fragment mass distributions in the Li6,7 + U238 reactions

S. Santra, A. Pal, P. K. Rath, B. K. Nayak, N. L. Singh, D. Chattopadhyay, B. R. Behera, Varinderjit Singh, A. Jhingan, P. Sugathan, K. S. Golda, S. Sodaye, S. Appannababu, E. Prasad, and S. Kailas
Phys. Rev. C 90, 064620 – Published 24 December 2014

Abstract

Background: Detailed studies on the effect of the breakup of weakly bound projectile on fission are scarce. Distinguishing the events of compound nuclear (CN) fission from the breakup or transfer induced fission to understand the properties of measured fission fragments is difficult but desirable.

Purpose: To investigate the effect of projectile breakup and its breakup threshold energy on fission-fragment (FF) mass distributions and folding angle distributions for Li6,7 + U238 reactions and find out the differences in the properties of the fission events produced by complete fusion (CF) from the total fusion (TF).

Methods: The FF mass and folding angle distributions have been measured at energies around the Coulomb barrier using gas detectors by time-of-flight technique. The results are compared with the ones involving tightly bound projectiles as well as predictions from systematics to bring out the effect of the breakup.

Results: A sharp increase in the peak to valley (P:V) ratio of FF mass distribution with the decrease in bombarding energy for Li6,7 + U238 reactions is observed when all events are assumed to be CN fission. As the beam energy falls through the fusion barrier, the full width half maximum (FWHM) of the FF folding angle distribution is found to increase at sub-barrier energies, unlike the reactions involving tightly bound projectiles where a linear decrease in FWHM is expected. By selecting pure CN events from the scatter plot of the velocity components of the composite nuclei, the energy dependence of the deduced FWHM is found to be consistent with the ones involving tightly bound projectiles. Similarly, the P:V ratio obtained for the selected CN events is consistent with the theoretical calculations as well as the experimental data for the proton induced reaction forming similar CN.

Conclusions: The presence of projectile breakup induced fission and a relatively low breakup threshold for Li6 compared to Li7 explains the observed differences in the energy dependence of the P:V ratio and the FWHM of FF folding angle distributions for CF and TF fission in the present reactions.

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  • Received 14 October 2014
  • Revised 13 November 2014

DOI:https://doi.org/10.1103/PhysRevC.90.064620

©2014 American Physical Society

Authors & Affiliations

S. Santra1,*, A. Pal1, P. K. Rath2, B. K. Nayak1, N. L. Singh2, D. Chattopadhyay1, B. R. Behera3, Varinderjit Singh3, A. Jhingan4, P. Sugathan4, K. S. Golda4, S. Sodaye5, S. Appannababu2, E. Prasad6, and S. Kailas1,7

  • 1Nuclear Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India
  • 2Department of Physics, The M. S. University of Baroda, Vadodara 390002, India
  • 3Department of Physics, Panjab University, Chandigarh, India
  • 4Inter University Accelerator Centre, Aruna Asaf Ali Marg, New Delhi 110067, India
  • 5Radio Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400085, India
  • 6Department of Physics, Central University of Kerala, Kasaragod, Kerala 671123, India
  • 7UM-DAE Centre for Excellence in Basic Sciences, University of Mumbai, Mumbai 400 098, India

  • *ssantra@barc.gov.in

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Vol. 90, Iss. 6 — December 2014

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