Excitation-energy dependence of fission-fragment neutron multiplicity in the improved scission-point model

For the neutron-induced fission of nuclei ${}^{235,238}\mathrm{U}$, the evolution of the shape of fission-fragment neutron multiplicity distribution with increasing excitation energy is explored within the improved scission-point model. For a wide range of incident neutron energies, the dependence of an average number of neutrons emitted per a fission event on the excitation energy is studied.

Figure 1

The mass distribution of the fission fragments originating from the neutron-induced fission of ${}^{238}\mathrm{U}$ as a function of the mass number of one of the fragments. The solid lines represent theoretical results and the symbols are experimental data [23, 24] and [25] at the incident neutron energies $E_n=$ 0.5, 5.8, 14, 22.5 and 32.8, 45, 59.9 MeV, respectively.

Figure 2

The average neutron multiplicity distribution $\langle \nu \rangle \left(A_i\right)$ as a function of the mass number of one of the fragments resulting from the ${}^{238}\mathrm{U}(n,f)$ reaction. The incident neutron energy $E_n$ is indicated in each panels.

Figure 3

The average neutron multiplicity distribution $\langle \nu \rangle \left(Z_i\right)$ as a function of the charge number of one of the fragments resulting from the ${}^{238}\mathrm{U}(n,f)$ reaction. The incident neutron energy is indicated in each panels.

Figure 4

The PES corresponding to the ${}^{99}\mathrm{Sr}+{}^{140}\mathrm{Te}$ fragmentation of ${}^{239}\mathrm{U}$. The incident neutron energies are (a) $E_n=0.5$ MeV and (b) $E_n=59.9$ MeV.

Figure 5

The calculated probabilities $P\left(\nu \right)$ (lines) as functions of the neutron multiplicity $\nu$ and the calculated average number of neutrons $\langle \nu \rangle$ (thick red line) emitted per a fission event in the case of the ${}^{238}\mathrm{U}(n,f)$ reaction at the indicated neutron energies $E_n$. The symbols represent the experimental [28, 29] results for the $\langle \nu \rangle$ at different $E_n$.

Figure 6

The same as in Fig. 1 but for the ${}^{235}\mathrm{U}(n,f)$ reaction at the indicated neutron energies.

Figure 7

The calculated (red solid lines) and experimental (the dash-dotted line [30] and symbols [31]) average neutron multiplicity distributions $\langle \nu \rangle \left(A_i\right)$ (the right axis) as a function of the mass number of one of the fragments resulting from the ${}^{235}\mathrm{U}(n,f)$ reaction. The incident neutron energy $E_n$ is indicated in each panel. The calculated deformation $\langle U^{\text{def}}\rangle \left(A_i\right)$ (solid lines) and excitation $\langle E^{*}\rangle \left(A_i\right)$ (dashed lines) energies of fission fragments at scission (the left axis).

Figure 8

The same as in Fig. 3 but for the ${}^{235}\mathrm{U}(n,f)$ reaction at the indicated neutron energies.

Figure 9

The same as in Fig. 5 but for the ${}^{235}\mathrm{U}(n,f)$ reaction at the indicated neutron energies.

Figure 10

The average total kinetic energy $\langle \text{TKE}\rangle$ of the fission fragments as a function of incident neutron energy for the ${}^{235}\mathrm{U}(n,f)$ reaction. The solid line represents the theoretical results, while the symbols are the experimental data of Ref. [32].