New statistical scission-point model to predict fission fragment observables

The development of high performance computing facilities makes possible a massive production of nuclear data in a full microscopic framework. Taking advantage of the individual potential calculations of more than 7000 nuclei, a new statistical scission-point model, called SPY, has been developed. It gives access to the absolute available energy at the scission point, which allows the use of a parameter-free microcanonical statistical description to calculate the distributions and the mean values of all fission observables. SPY uses the richness of microscopy in a rather simple theoretical framework, without any parameter except the scission-point definition, to draw clear answers based on perfect knowledge of the ingredients involved in the model, with very limited computing cost.

Figure 1

Liquid drop (orange dotted line), HFB (green dashed line), and shifted HFB (blue solid line) potential energy as a function of deformation for ${}^{132}\mathrm{Sn}$ (a), ${}^{104}\mathrm{Mo}$ (b), and ${}^{118}\mathrm{Pd}$ (c). Liquid drop ground state energy is shifted to HFB ground state energy.

Figure 2

Integration mesh for ${}^{132}\mathrm{Sn}$ with quadrupole deformation $\tilde{q}=0.4$. The points and the dotted lines represent vertices and edges of the elementary volumes.

Figure 3

Coulomb energy between two fragments (fragment 1: ${}^{132}\mathrm{Sn}$; fragment 2: ${}^{104}\mathrm{Mo}$) as a function of their quadrupole deformation.

Figure 4

Available energy as a function of the fragments deformation calculated for symmetric (${}^{118}\mathrm{Pd}+{}^{118}\mathrm{Pd}$) fragmentation in the ${}^{235}\mathrm{U}(n_{th},f)$ reaction.

Figure 5

Available energy as a function of the fragments deformation calculated for asymmetric (${}^{132}\mathrm{Sn}+{}^{104}\mathrm{Mo}$) fragmentation in the ${}^{235}\mathrm{U}(n_{th},f)$ reaction.

Figure 6

Maximum available energy as a function of the fragment proton and neutron numbers in the ${}^{235}\mathrm{U}(n_{th},f)$ reaction.

Figure 7

Fragment mass (a) and charge (b) yields in the ${}^{235}\mathrm{U}(n_{th},f)$ reaction calculated with SPY (in red) compared to evaluated data (post neutron evaporation) from the ENDF/B-VII.1 data library (in black) [26].

Figure 8

Mean fragment deformation in the ${}^{235}\mathrm{U}(n_{th},f)$ reaction.

Figure 9

Fission fragment kinetic energy in the ${}^{235}\mathrm{U}(n_{th},f)$ reaction calculated with SPY (red line) compared to experimental data from Baba [27] (black line).

Figure 10

Mean fragment deformation calculated with SPY (red, right scale) in the ${}^{235}\mathrm{U}(n_{th},f)$ reaction, compared to the experimental mean number of evaporated neutrons $\nu$ (black, left scale) from Vorobyev [28].

Figure 11

Mean available energy as a function of the fragment mass for different scission distances in the ${}^{235}\mathrm{U}(n_{th},f)$ reaction.

Figure 12

Fragment kinetic energy for different scission distances in the ${}^{235}\mathrm{U}(n_{th},f)$ reaction calculated with SPY, compared to experimental data from Baba [27] (black line).

Figure 13

Fragment mass yields in the ${}^{235}\mathrm{U}(n_{th},f)$ reaction calculated within the canonical framework at different temperatures and compared to the microcanonical description.

Figure 14

Mass yields in the thermal neutron-induced fission of different actinides calculated with SPY (in red) and compared to evaluated data from the ENDF/B-VII.1 data library [26].

Figure 15

Charge yields for the fission of light actinides region calculated with SPY (in red) compared to data from Schmidt [9] (in black).

Figure 16

Mean kinetic energy as a function of the compound nucleus fissility calculated with SPY (in red) compared to experimental data [33] (in black) and to the Viola formula [32] (black line).

Figure 17

Peak multiplicity in the mass yields as a function of the compound nucleus for an excitation energy of 8 MeV.

Figure 18

Estimated mean prompt neutron multiplicity per fragment as a function of the compound nucleus for an excitation energy of 8 MeV.