Fission time scale from prescission neutron, proton, and α particle multiplicities in ${}^{28}\mathrm{Si}$+${}^{175}\mathrm{Lu}$

Prescission neutron, proton, and α-particle multiplicities for the reaction ${}^{28}\mathrm{Si}$+${}^{175}\mathrm{Lu}$ at 159 MeV were measured simultaneously. The multiplicity data were analyzed using deformation dependent particle transmission coefficients, binding energies, and level densities to extract fission time scales and the mean deformation of the saddle-to-scission emitter. The neutron and charged particle data could be explained consistently, a better fit being obtained by considering the emission of neutrons to be favored toward larger deformation as compared to charged particles. The total fission time scale is deduced as $36\text{−}41\times {10}^{-21}$s.

Figure 1

Schematic representation of the experimental setup. The expanded view of the Si strip detector shows the way the middle and outer strips are connected (see text).

Figure 2

Neutron multiplicity spectra (filled circles) along with fits using the moving source formula. These spectra corresponds to various relative angles between neutrons and detected fission fragments. The solid curves indicate total contribution from all sources. The dotted, dashed, and dot-dashed curves are contributions from the compound nucleus, detected fission fragment, and complementary fission fragment, respectively.

Figure 3

Proton multiplicity spectra (solid circles) along with fits using the moving source formula. These spectra corresponds to various relative angles between protons and detected fission fragments. The solid curves indicate total contribution from all sources. The dotted, dashed, and dot-dashed curves are contributions from the compound nucleus, detected fission fragment, and complementary fission fragment respectively.

Figure 4

Same as Fig. 3 for α-particles along with near scission emission. The solid curves indicate total contribution from all sources. The dotted, dashed, dot-dashed, and medium dashed curves are contributions from compound nucleus, detected fission fragment, complementary fission fragment, and near scission emission, respectively.

Figure 5

The potential energy diagram for ${}^{203}\mathrm{At}$ showing deformation energy as a function of deformation $Z_{\mathrm{axis}}$ for angular momentum, $J=0$, 35.6 $\hslash$ (average of compound nucleus angluar distribution).

Figure 6

Combinations of ${\tau }_{\mathrm{tr}}$ and ${\tau }_{\mathrm{ssc}}$ required to reproduce experimental ${\nu }_{\mathrm{pre}},{\pi }_{\mathrm{pre}}$ and ${\alpha }_{\mathrm{pre}}$ data, respectively, are shown as line, long dashed, and medium dashed lines, respectively, for (a) Z${}_{\mathrm{ssc}}=$ 2.17, (b) Z${}_{\mathrm{ssc}}=$ 2.45, and (c) Z${}_{\mathrm{ssc}}=$ 2.45 for neutron emission and Z${}_{\mathrm{ssc}}=$ 1.90 for charged-particle emission. The shaded regions correspond to experimental errors.