Pre- and post-scission neutron multiplicities in $\chem{^{19}F} + \chem{^{209}Bi}$ reaction at 108 MeV

L.M. Pant; A. Saxena; R.G. Thomas; D.C. Biswas; R.K. Choudhury

doi:doi:10.1140/epja/i2002-10072-2

2022 Impact factor 2.7

Hadrons and Nuclei

Eur. Phys. J. A 16, 43-50 (2003)
DOI: 10.1140/epja/i2002-10072-2

Pre- and post-scission neutron multiplicities in $\chem{^{19}F} + \chem{^{209}Bi}$ reaction at 108 MeV

L.M. Pant¹, A. Saxena¹, R.G. Thomas¹, D.C. Biswas¹ and R.K. Choudhury²

¹ Nuclear Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India
² Institute of Physics, Bhubaneshwar, India

lalit_pant@rediffmail.com

(Received: 15 March 2002 / Revised version: 23 August 2002 / Published online: 17 January 2003)

Abstract
The pre- and post-scission neutron multiplicities have been determined from the fragment-neutron angular-correlation measurements in $\chem{^{19}F}$ + $\chem{^{209}Bi}$ reaction at bombarding energy of 108 MeV. The average pre-scission neutron multiplicity ( ${\nu}^{\rm pre}$ ) is significantly larger than that calculated on the basis of the statistical model. The excess in ${\nu}^{\rm pre}$ value is used to estimate the dynamical delay in the fusion-fission time scale for the $\chem{^{228}U}$ compound system. For a level density parameter $a_{\rm n} = A/10$ MeV ^-1 and $a_{\rm n}$ = $a_{\rm f}$ , the fusion-fission dynamical time was established to be 120 ${\pm}$ 10 ${\times}$ 10 ^-21 s. We also observe that ${\nu}^{\rm pre}$ is higher for asymmetric mass splits as compared to symmetric mass splits. The enhancement in the ${\nu}^{\rm pre}$ for the asymmetric region could be due to strong variations in the fragment mass distribution at different stages in multiple chance fission at medium excitation energies.