Detailed statistical model analysis of observables from fusion-fission reactions

Tathagata Banerjee, S. Nath, and Santanu Pal
Phys. Rev. C 99, 024610 – Published 12 February 2019

Abstract

Background: Despite remarkable success of the statistical model (SM) in describing decay of excited compound nuclei (CN), reproduction of the observables from heavy ion-induced fusion-fission reactions is often quite challenging. Ambiguities in choosing the input parameters, lack of clarity about inclusion of various physical effects in the model, and contradictory requirements of input parameters while describing different observables from similar reactions are among the major difficulties of modeling decay of fissile CN.

Purpose: This work attempts to overcome the existing inconsistencies by inclusion of important physical effects in the model and through a systematic analysis of a large set of data over a wide range of CN mass (ACN).

Method: The model includes the shell effect in the level density (LD) parameter, shell correction in the fission barrier (Bf), the effect of the orientation degree of freedom of the CN spin (Kor), collective enhancement of level density (CELD), and dissipation in fission. Input parameters are not tuned to reproduce observables from specific reaction(s) and the reduced dissipation coefficient (β) is treated as the only adjustable parameter. Calculated evaporation residue (ER) cross sections (σER), fission cross sections (σfiss), and particle, i.e., neutron, proton, and α particle, multiplicities are compared with data covering ACN=156–248.

Results: The model produces reasonable fits to ER and fission excitation functions for all the reactions considered in this work. Pre-scission neutron multiplicities (νpre) are underestimated by the calculation beyond ACN200. An increasingly higher value of β, in the range of 2–4×1021s1, is required to reproduce the data with increasing ACN. Proton and α-particle multiplicities, measured in coincidence with both ERs and fission fragments, are in qualitative agreement with model predictions.

Conclusions: The present work mitigates the existing inconsistencies in modeling statistical decay of the fissile CN to a large extent. Contradictory requirements of fission enhancement—obtained by scaling down the fission barrier to reproduce σER or σfiss and fission suppression realized by introducing dissipation in the fission channel to reproduce νpre, for similar reactions—have now become redundant. There are scopes for further refinement of the model, as is evident from the mismatch between measured and calculated particle multiplicities in a few cases.

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  • Received 25 September 2018
  • Revised 20 January 2019

DOI:https://doi.org/10.1103/PhysRevC.99.024610

©2019 American Physical Society

Physics Subject Headings (PhySH)

Nuclear Physics

Authors & Affiliations

Tathagata Banerjee*, S. Nath, and Santanu Pal

  • Nuclear Physics Group, Inter University Accelerator Centre, Aruna Asaf Ali Marg, Post Box 10502, New Delhi 110067, India

  • *Present address: Department of Nuclear Physics, Research School of Physics and Engineering, The Australian National University, Canberra ACT 0200, Australia; he.tatha@gmail.com
  • Formerly with Physics Group, Variable Energy Cyclotron Centre, 1/AF Bidhan Nagar, Kolkata 700064, India.

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Vol. 99, Iss. 2 — February 2019

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