Comparison of yields of neutron-rich nuclei in proton- and photon-induced ${}^{238}\mathrm{U}$ fission

A comparative study of fission of actinides, especially ${}^{238}\mathrm{U}$, by proton and bremsstrahlung photon is performed. The relative mass distribution of ${}^{238}\mathrm{U}$ fission fragments has been explored theoretically for both proton- and photon-induced fission. The integrated yield along with charge distribution of the products are calculated to find the neutron richness in comparison with the nuclei produced by the $r$ process in nucleosynthesis. Some $r$-process nuclei in the intermediate-mass range for symmetric fission mode are found to be produced almost two orders of magnitude more for proton-induced fission than for photofission, although the rest of the neutron-rich nuclei in the asymmetric mode are produced in comparable proportion for both processes.

Figure 1

Comparison of the measured mass-yield distribution (solid squares) [24] for ${}^{238}\mathrm{U}$ fission induced by 12 MeV protons with the prediction (solid line) of the three-Gaussian formula for $Y\left(A\right)$ and GEF predictions [26].

Figure 2

Same as Fig. 1 (solid squares) [25] but for a different proton energy of 35 MeV.

Figure 3

Variation of symmetric and asymmetric Gaussian parameters with excitation energies.

Figure 4

Comparison of total fission cross section (solid squares) [22, 23] of ${}^{238}\mathrm{U}$ by protons with energies in the range 13–63 MeV with the prediction (solid line) from our calculation, talys and pace4.

Figure 5

Variation of ratio of cross sections (35 MeV $p/13.7$ MeV photon) with fragment mass number for $A/Z=2.66$.

Figure 6

Same as Fig. 5 but for $A/Z=2.5$.

Figure 7

Two-dimensional contour plots for the ratio of proton- and $\gamma$-induced ${}^{238}\mathrm{U}$ fission cross sections vs atomic number $Z$ and neutron number $N$. These ratios are represented by different color shades corresponding to the different values mentioned in the figure.

Figure 8

Plots of atomic number $Z$ vs neutron number $N$ for exotic nuclei produced by photon- and proton-induced fission of ${}^{238}\mathrm{U}$.