Light charged particles emitted in fission reactions induced by protons on ${}^{208}\mathrm{Pb}$

Light charged particles emitted in proton-induced fission reactions on ${}^{208}\mathrm{Pb}$ have been measured at different kinetic energies: $370A,500A$, and $650A$ MeV. The experiment was performed by the SOFIA Collaboration at the GSI facilities in Darmstadt (Germany). The inverse kinematics technique was combined with a setup especially designed to measure light charged particles in coincidence with fission fragments. This measurement allowed us, for the first time, to obtain correlations between the light charged particles emitted during the fission process and the charge distributions of the fission fragments. These correlations were compared with different model calculations to assess the ground-to-saddle dynamics. The results confirm that transient and dissipative effects are required for an accurate description of the fission observables.

Figure 1

(a) Schematic diagram of the experimental setup used to measure the light charged particles in coincidence with fission. Sizes are not to scale. (b) Schematic view of the ToF wall used to detect the light charged particles.

Figure 2

(a) Identification of light charged particles emitted in fission in the scintillators of the ToF wall. The solid ellipses indicate the different particles. The inset shows the projection of the charge distribution. (b) Total correction factor for light charged particles with $Z=1$ as a function of its multiplicity. These correction factors are calculated for the three kinetic energies investigated in this work. The uncertainties are shown with dashed areas.

Figure 3

The measured distribution of particles with $Z=1$ for the reaction ${}^{208}\mathrm{Pb}+p$ at $650A$ MeV is shown in comparison to the one after corrections. The uncertainties are shown if they exceed the size of the symbols. The solid line represents a Gaussian extrapolation.

Figure 4

(a) Multiplicity distribution of particles with $Z=1$ for the reaction ${}^{208}\mathrm{Pb}+p$ at different kinetic energies: $370A$ (open triangles), $500A$ (solid circles), and $650A$ (open squares) MeV. The lines are to guide the eye. (b) Width of the atomic-number distribution of the final fission fragments as a function of the atomic number of the removed light charged particle from the projectile. The data for the reaction ${}^{208}\mathrm{Pb}+{}^{27}\mathrm{Al}$ at $500A$ MeV (solid triangles) are also displayed. The inset shows the excitation energy as a function of the size of the emitted particle, where the dashed area indicates the width of the distribution.

Figure 5

(a) Average multiplicity of particles with $Z=1$ as a function of the projectile bombarding energy for the reaction ${}^{208}\mathrm{Pb}+p$. (b) Width of the atomic-number distribution of the final fission fragments measured in the reaction ${}^{208}\mathrm{Pb}(500A \mathrm{MeV}) +p$ as a function of the atomic number of the removed light particle from the projectile. In both figures the data are compared with different model calculations (lines).