Yields of neutron-rich nuclei by actinide photofission in the giant dipole resonance region

The photonuclear reactions of actinides induced by bremsstrahlung $\gamma \text{s}$ are studied in the region of nuclear excitation energies that covers the entire giant dipole resonance region. A comparative analysis of the behavior of the symmetric and asymmetric modes of photon-induced fission as a function of the average excitation energy of the fissioning nucleus is performed. The mass distributions for photofission fragments are obtained. The integrated yield as well as charge distribution of photofission products is determined. Thus, the production cross sections of neutron-rich nuclei are calculated and their exoticity (neutron richness) is explored in comparison to the nuclei produced by rapid neutron capture process in nucleosynthesis.

Figure 1

Comparison of the measured photoabsorption and photofission cross sections (full circles) [18] for ${}^{238}\mathrm{U}$ as functions of incident photon energy with predictions (solid lines) of the hydrodynamic theory of photonuclear reactions for the giant dipole resonance region that consists of Lorentz line shapes for spherical nuclei. The dotted line represents photofission cross sections obtained by using the ratio method.

Figure 2

Comparison of the measured mass yield distribution (full circles) for ${}^{238}\mathrm{U}$ photofission induced by bremsstrahlung photons having mean photon energy of 13.7 MeV [13] with the prediction (solid line) of the five Gaussian formula for $Y\left(A\right)$. The dotted lines represent individual contributions of one symmetric Gaussian and two asymmetric double Gaussians.

Figure 3

Plot of fractional yield $DY(A,Z)$ as a function of charge number $Z$ for fragment mass number $A=97$ of ${}^{238}\mathrm{U}$ photofission. Experimental data [13] are shown with full circles while the solid line represents the Gaussian charge distribution.

Figure 4

Plots of atomic number $Z$ vs neutron number $N$ for exotic nuclei produced by the photofission of ${}^{238}\mathrm{U}$ by bremsstrahlung $\gamma \text{s}$ with mean photon energy of 13.7 MeV.