Independent isomeric yield ratios and primary angular momenta in the photofission ofU235,238with 12-30-MeV bremsstrahlung

The independent isomeric yield ratios for ${}_{}{}^{129}{}_{}{}^{}\mathrm{Sn}$, ${}_{}{}^{130}{}_{}{}^{}\mathrm{Sb}$, ${}_{}{}^{131}{}_{}{}^{}\mathrm{Sn}$, ${}_{}{}^{132}{}_{}{}^{}\mathrm{Sb}$, ${}_{}{}^{133}{}_{}{}^{}\mathrm{Te}$, and ${}_{}{}^{136}{}_{}{}^{}\mathrm{I}$ for the photofission of ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$ with 12-30-MeV bremsstrahlung and for ${}_{}{}^{126}{}_{}{}^{}\mathrm{Sb}$, ${}_{}{}^{129}{}_{}{}^{}\mathrm{Sn}$, ${}_{}{}^{130}{}_{}{}^{}\mathrm{Sb}$, ${}_{}{}^{131}{}_{}{}^{}\mathrm{Sn}$, ${}_{}{}^{132}{}_{}{}^{}\mathrm{Sb}$, ${}_{}{}^{133}{}_{}{}^{}\mathrm{Te}$, and ${}_{}{}^{136}{}_{}{}^{}\mathrm{I}$ for the photofission of ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ have been determined using radiochemical techniques and gamma spectrometry of fission product catcher foils and irradiated uranium samples. The root-mean-square values of the primary angular momenta of the corresponding fission fragments, $J_{\mathrm{rms}}$, were calculated with the statistical procedure of Huizenga and Vandenbosch and with the more elaborate deexcitation model of Min and Martinot. Both procedures gave, except for ${}_{}{}^{130}{}_{}{}^{}\mathrm{Sb}$, almost the same $J_{\mathrm{rms}}$ values. Our experimental results show a near independency of $J_{\mathrm{rms}}$ on the spin and excitation energy of the compound nucleus. An increase of the $J_{\mathrm{rms}}$ values with the excitation energy of the fragments is observed. In addition, a significant proton odd-even effect on the $J_{\mathrm{rms}}$ values is present for the photofission of ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$ as well as ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$. Our experimental photofission results show a qualitative agreement with the theoretical calculations of Dietrich and Zielinska-Pfabé.