The independent yield ratios of $\frac{(30\mathrm{}-\mathrm{h} {\mathrm{Te}}^{131m})}{(25\mathrm{}-\mathrm{m}\mathrm{i}\mathrm{n} {\mathrm{Te}}^{131})}$ and of $\frac{(53\mathrm{}-\mathrm{m}\mathrm{i}\mathrm{n} {\mathrm{Te}}^{133m})}{(12.5\mathrm{}-\mathrm{m}\mathrm{i}\mathrm{n} {\mathrm{Te}}^{133})}$ were measured in the following types of fission: ${\mathrm{U}}^{235}$ with thermal neutrons, and ${\mathrm{Th}}^{232}$ and ${\mathrm{U}}^{238}$ with 18-MeV deuterons and with 33-MeV ${\mathrm{He}}^4$ ions. The fractional independent chain yields of the isomers were measured by determining the growth curves of the daughter iodine activities extracted at successive time intervals from aliquots of samples containing tellurium activities quickly separated from fission induced in short irradiations, and correcting for contributions from precursors. The isomer-yield ratios for independent formation for $\frac{30-\mathrm{h} {\mathrm{Te}}^{131m}}{25-\mathrm{m}\mathrm{i}\mathrm{n} {\mathrm{Te}}^{131}}$ and for $\frac{53-\mathrm{m}\mathrm{i}\mathrm{n} {\mathrm{Te}}^{133m}}{12.5-\mathrm{m}\mathrm{i}\mathrm{n} {\mathrm{Te}}^{133}}$, respectively, are as follows: 1.8±0.4 and 1.55±0.5 for ${\mathrm{U}}^{235}(n_{\mathrm{th}},F)$, 3.3±0.5 and 2.8±1.7 for ${\mathrm{Th}}^{232}({\alpha }_{33},F)$, 2.7±0.5 and 1.7±0.9 for ${\mathrm{Th}}^{232}(d_{18},F)$, 5.0±1.0 and 3.1±2.0 for ${\mathrm{U}}^{238}({\alpha }_{33},F)$, and 3.3±0.5 and 1.8±1.1 for ${\mathrm{U}}^{238}(d_{18},F)$. The fractional independent chain yield of ${\mathrm{Te}}^{131m}+{\mathrm{Te}}^{131}$ was measured as 0.124±0.014 for ${\mathrm{U}}^{235}(n_{\mathrm{th}},F)$. The fraction of decay of ${\mathrm{Sb}}^{131}$ to ${\mathrm{Te}}^{131m}$ was measured and found to be 6.8±1%. On the basis of the measured isomer ratios, the intrinsic spin of the primary fragment (leading by the emission of neutrons and $\gamma$ rays to the secondary fragments studied) was estimated. The calculations indicate that in thermal-neutron fission an appreciably larger spin ($\sim 5\hslash$) than that of the compound nucleus must be assigned to the heavy primary fragment in order to explain the observed isomer ratios in ${\mathrm{Te}}^{131}$ and ${\mathrm{Te}}^{133}$. Similar reasoning in the 33-MeV ${\mathrm{He}}^4$-ion fission of ${\mathrm{Th}}^{232}$ indicates that the primary fragment must be given an intrinsic spin value roughly $7\hslash$.

• Received 2 December 1964

DOI:https://doi.org/10.1103/PhysRev.138.B353