Anomalous deviations from statistical evaporation spectra for the decay of the 73Br and 77Rb compound systems

Maninder Kaur, B. R. Behera, Gulzar Singh, Varinderjit Singh, Rohit Sandal, A. Kumar, H. Singh, Gurpreet Singh, K. P. Singh, N. Madhavan, S. Nath, A. Jhingan, J. Gehlot, K. S. Golda, P. Sugathan, Davinder Siwal, Sunil Kalkal, E. Prasad, and S. Appannababu
Phys. Rev. C 89, 034621 – Published 26 March 2014

Abstract

Background: Several inclusive and few exclusive [evaporation residue (ER) gated] measurements for symmetric systems reported in the literature describe the anomalous deviations of light particle evaporation spectra from the statistical model predictions. However, no consistent description exists for these deviations.

Purpose: To establish the consistent interpretation of reported anomalous deviations.

Method: The inclusive and exclusive measurements of α-particle, proton, and neutron spectra were carried out for the fusion of two relatively symmetric systems 28Si + 45Sc (Elab = 125 MeV and lmax = 47) and 32S + 45Sc (Elab = 125 MeV and lmax = 43) leading to the compound nuclei 73Br and 77Rb with excitation energies 78 MeV and 71 MeV, respectively.

Results: The experimental light particle spectra for both the reactions show anomalous deviations from the statistical model predictions. The charged particles spectra are found to be suppressed, whereas the neutron spectra exhibit a bump at the higher energy tail. These spectra are investigated in terms of the modification of the important ingredients of the statistical model viz. the level density parameter, rescaling of the yrast line, and the use of l value suggested by the dynamical models.

Conclusions: It is conjectured that the higher partial waves do not fuse, but result in the formation of a deformed dinuclear system. The binding energy of neutrons is reduced while those for protons and α particles are enhanced in the deformed dinuclear system as compared to those in the shape-equilibrated system. Hence, the higher partial waves inhibit their contributions to the α-particle spectra and lead to the preshape equilibrium of neutrons and protons, with the neutron emission dominating over the proton emission.

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  • Received 9 August 2013
  • Revised 12 February 2014

DOI:https://doi.org/10.1103/PhysRevC.89.034621

©2014 American Physical Society

Authors & Affiliations

Maninder Kaur, B. R. Behera*, Gulzar Singh, Varinderjit Singh, Rohit Sandal, A. Kumar, H. Singh§, Gurpreet Singh, and K. P. Singh

  • Department of Physics, Panjab University, Chandigarh 160014, India

N. Madhavan, S. Nath, A. Jhingan, J. Gehlot, K. S. Golda, and P. Sugathan

  • Inter University Accelerator Centre, Aruna Asaf Ali Marg, New Delhi 110067, India

Davinder Siwal and Sunil Kalkal

  • Department of Physics and Astrophysics, University of Delhi, Delhi 110007, India

E. Prasad

  • Department of Physics, University of Calicut 673635, India

S. Appannababu

  • Department of Physics, Faculty of Science, The M. S. University of Baroda, Vadodara 390002, India

  • *Corresponding author: bivash@pu.ac.in
  • Present address: Centre for Physical and Mathematical Sciences, Central University of Punjab, Bathinda 151001, India.
  • Present address: Department of Physics, S.V. Government College Ghumarwin, Bilaspur (H.P.) 174021, India.
  • §Present address: Department of Physics, Kurukshetra University, Kurukshetra, Haryana 136119, India.
  • Present address: Department of Physics, School of Mathematical and Physical Sciences, Central University of Kerala, Kasaragod 671314, India.
  • Present address: INFN, Laboratori Nazionali di Legnaro, I-35020 Legnaro (Padova), Italy.

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Issue

Vol. 89, Iss. 3 — March 2014

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