220
R. Mahajan
Sagaidak et al. [7] have analyzed the ER and fission excitation functions data
obtained in complete fusion reactions leading to Po compound nuclei in the framework of the standard statistical model. They have observed a drop in the Po fission
barriers with the decrease in a neutron number, which is supported by the presence
of entrance channel effects and collective excitations in the CN decay. Mahata et
al. [8] have also suggested the lowering the fission barrier (saddle point) from the
statistical model (SM) analysis of the prefission neutron multiplicity data for
210 Po
in excitation energy range of ≈40–60 MeV.
It is now well established that the fission process is somewhat delayed with respect
to the statistical picture of CN decay due to the presence of dissipation. It affects many
experimental observables like pre-scission particle multiplicities, fission probability,
and mass-energy distribution of fission fragments. Neutron emission that acts as a
clock to measure the fission time scale has proved to be very useful in investigating the
mechanism of nuclear fission [9]. This is because neutrons are emitted in succession
from a hot CN till it fissions and thus the pre-scission neutron multiplicity becomes
a measure of the time scale of fission. Therefore, in order to address these problems
in the actinide region, a detailed study of the decay products of the CN, such as ERs,
CN fission fragments are necessary. In this regard, ER, fission cross-section and
neutron multiplicity measurements can be a useful probe to understand the fusion–
fission dynamics. In view of this, we have extended our theoretical investigation to
understand the fission dynamics in actinide region by considering different isotopes
of Po [10, 11].
With these motivations, we have performed SM calculations for
210 Po CN populated through
16 O +
192 Os in the excitation energy range 52.43–83.51 MeV for which
experimental data on ER, fission cross-section, and neutron multiplicity is already
available in the literature [9]. In this chapter, results of the SM calculations have been
presented.
This first section of this chapter deals with various ingredients used in the SM and
the results of the analysis obtained for ER and fission cross-section. The results of
neutron multiplicity for
210 Po CN are given in Sect. 16.2. The last section contains
the interpretation of the results obtained from the SM analysis.
16.2 Statistical Model Analysis of Evaporation Residue
and Fission Cross-Section
Sagaidak et al. [7] have also performed the similar systematic study of Po compound
nuclei utilizing the standard approach, in which CN production (fusion) and deexcitations are considered independently. The barrier-passing (BP) model takes care
of the fusion part, whereas the CN de-excitation is treated within the standard statistical approach (SSM). Both of them are implemented within the HIVAP code [12]. For
the present work, theoretical calculations were performed using Bohr–Wheeler formalism including shell-corrections in the level density and fission barrier in order to
R. Mahajan
Sagaidak et al. [7] have analyzed the ER and fission excitation functions data
obtained in complete fusion reactions leading to Po compound nuclei in the framework of the standard statistical model. They have observed a drop in the Po fission
barriers with the decrease in a neutron number, which is supported by the presence
of entrance channel effects and collective excitations in the CN decay. Mahata et
al. [8] have also suggested the lowering the fission barrier (saddle point) from the
statistical model (SM) analysis of the prefission neutron multiplicity data for
210 Po
in excitation energy range of ≈40–60 MeV.
It is now well established that the fission process is somewhat delayed with respect
to the statistical picture of CN decay due to the presence of dissipation. It affects many
experimental observables like pre-scission particle multiplicities, fission probability,
and mass-energy distribution of fission fragments. Neutron emission that acts as a
clock to measure the fission time scale has proved to be very useful in investigating the
mechanism of nuclear fission [9]. This is because neutrons are emitted in succession
from a hot CN till it fissions and thus the pre-scission neutron multiplicity becomes
a measure of the time scale of fission. Therefore, in order to address these problems
in the actinide region, a detailed study of the decay products of the CN, such as ERs,
CN fission fragments are necessary. In this regard, ER, fission cross-section and
neutron multiplicity measurements can be a useful probe to understand the fusion–
fission dynamics. In view of this, we have extended our theoretical investigation to
understand the fission dynamics in actinide region by considering different isotopes
of Po [10, 11].
With these motivations, we have performed SM calculations for
210 Po CN populated through
16 O +
192 Os in the excitation energy range 52.43–83.51 MeV for which
experimental data on ER, fission cross-section, and neutron multiplicity is already
available in the literature [9]. In this chapter, results of the SM calculations have been
presented.
This first section of this chapter deals with various ingredients used in the SM and
the results of the analysis obtained for ER and fission cross-section. The results of
neutron multiplicity for
210 Po CN are given in Sect. 16.2. The last section contains
the interpretation of the results obtained from the SM analysis.
16.2 Statistical Model Analysis of Evaporation Residue
and Fission Cross-Section
Sagaidak et al. [7] have also performed the similar systematic study of Po compound
nuclei utilizing the standard approach, in which CN production (fusion) and deexcitations are considered independently. The barrier-passing (BP) model takes care
of the fusion part, whereas the CN de-excitation is treated within the standard statistical approach (SSM). Both of them are implemented within the HIVAP code [12]. For
the present work, theoretical calculations were performed using Bohr–Wheeler formalism including shell-corrections in the level density and fission barrier in order to