Energy dependence of mass, charge, isotopic, and energy distributions in neutron-induced fission of ${}^{235}\mathrm{U}$ and ${}^{239}\mathrm{Pu}$

The mass, charge, isotopic, and kinetic-energy distributions of fission fragments are studied within an improved scission-point statistical model in the reactions ${}^{235}\mathrm{U}+n$ and ${}^{239}\mathrm{Pu}+n$ at different energies of the incident neutron. The charge and mass distributions of the electromagnetic- and neutron-induced fission of ${}^{214,218}\mathrm{Ra},{}^{230,232,238}\mathrm{U}$ are also shown. The available experimental data are well reproduced and the energy-dependencies of the observable characteristics of fission are predicted for future experiments.

Figure 1

The calculated charge distribution (solid circles connected by dotted lines to guide eye) for fission of ${}^{235}\mathrm{U}$ by thermal neutron is compared with the experimental data (symbols) from Refs. [28, 29, 30]. The calculations were performed for even-$Z_i$ fragments.

Figure 2

The calculated charge distributions (solid circles connected by dotted lines to guide eye) in the electromagnetic-induced fission reactions (a) ${}^{230}\mathrm{U}$, (b) ${}^{232}\mathrm{U}$, (c) ${}^{214}\mathrm{Ra}$, and (d) ${}^{218}\mathrm{Ra}$ are compared with the experimental data (symbols) from Ref. [2]. The average excitation energy of these fissioning nuclei is about of 11 MeV [2]. The calculations were performed for even-$Z_i$ fragments.

Figure 3

The calculated mass distribution (solid line) for fission of ${}^{235}\mathrm{U}$ by thermal neutron is compared with the experimental data (symbols) from Refs. [28, 31].

Figure 4

The calculated mass distributions (solid lines) for fission of ${}^{235}\mathrm{U}$ by neutron with incident energies (a) 6 MeV and (b) 14 MeV. The experimental data (symbols) are from Ref. [32].

Figure 5

The calculated fragment mass distribution (solid lines) is compared with the experimental data [15] for the ${}^{238}\mathrm{U}$($n$,f) reaction at indicated incident neutron energies (a) 32.8, (b) 45.3, and (c) 59.9 MeV.

Figure 6

The calculated mass yields (solid lines) of the (a) Kr, (b) Sr, and (c) Zr isotopes as a function of neutron number $N_L$ in fission of ${}^{235}\mathrm{U}$ by thermal neutrons. The neutron emissions from the primary fragments were taken into consideration. The experimental data (symbols) are from Ref. [28].

Figure 7

The calculated (solid line) and experimental (symbols) [13] average total kinetic energies as functions of fragment mass in fission of ${}^{235}\mathrm{U}$ by thermal neutrons.

Figure 8

(a) The calculated fragment mass and (b) charge distributions in the ${}^{235}\mathrm{U}$($n$,f) reaction at the incident neutron energies indicated. The calculations were performed for even-$Z_i$ fragments.

Figure 9

The calculated potential-energy surfaces (in MeV) for the DNS with $(A_L,Z_L)=(96,36)$ and $(A_H,Z_H)=(140,56)$ at (a) $E_n=0\mathrm{MeV}$ and (b) $E_n=55\mathrm{MeV}$. The value of potential energy is normalized to the energy of the DNS with the spherical nuclei $\left({\beta }_L={\beta }_H=1\right)$. In the nuclear shape parametrization used, the value of quadrupole deformation parameter is approximately ${\beta }_i-1 \left(i=L,H\right)$.

Figure 10

The calculated isotopic trends for the nuclei (a) Kr, (b) Sr, (c) Zr, and (d) Mo in the ${}^{235}\mathrm{U}$($n$,f) reaction at different indicated neutron energies.

Figure 11

The calculated (solid circles connected by dotted lines to guide eye) fragment charge distribution in the ${}^{239}\mathrm{Pu}$($n_{th}$,f) reaction is compared with the experimental data (symbols) from Refs. [25, 26]. The calculations were performed for even-$Z_i$ fragments.

Figure 12

The calculated (solid line) fragment mass distribution in the ${}^{239}\mathrm{Pu}$($n_{th}$,f) reaction is compared with the experimental data (symbols) from Ref. [27].

Figure 13

The calculated (solid line) average total kinetic energies of fission fragments in the ${}^{239}\mathrm{Pu}$($n_{th}$,f) reaction versus fragment mass. The experimental data (symbols) are from Ref. [27].

Figure 14

The (a) charge and (b) mass distributions predicted for the ${}^{239}\mathrm{Pu}$($n$,f) reaction at different indicated neutron energies. The calculations were performed for even-$Z_i$ fragments.

Figure 15

The predicted isotopic trends for (a) the nuclei Kr, (b) Sr, (c) Zr, and (d) Mo in the ${}^{239}\mathrm{Pu}$($n$,f) reaction at indicated neutron energies.