A sample of europium which had been subjected to slow neutron irradiation was analyzed using mass spectrometric techniques. By using a modified isotopic dilution technique, i.e., adding a standard containing known relative abundances of normal samarium, europium, and gadolinium the complete chemical and isotopic analysis of the irradiated sample was obtained. Combining this nuclide composition and certain radioactivity measurements the thermal neutron cross sections, half-lives and branching ratios of five of the europium isotopes were calculated. The results were ${\sigma }_{151}=5200\mathrm{}$ barns, ${\sigma }_{152}=3200\mathrm{}$ barns, ${\sigma }_{153}=240\mathrm{}$ barns, ${\sigma }_{154}=880\mathrm{}$ barns, ${\sigma }_{155}=7900\mathrm{}$ barns, $T_{\frac{1}{2}}\mathrm{}\left(152\right)=5.3\mathrm{}$ years, $T_{\frac{1}{2}}\mathrm{}\left(154\right)=5.4\mathrm{}$ years, $T_{\frac{1}{2}}\mathrm{}\left(155\right)=1.7\mathrm{}$ years, $\frac{K}{{\beta }^{-}}$ ratio for 9.2-hr. ${\mathrm{Eu}}^{152}$=0.22, $\frac{K}{{\beta }^{-}}$ ratio for 5.3-year ${\mathrm{Eu}}^{152}$=2.8, and $\frac{K}{{\beta }^{-}}$ ratio for 5.4-year ${\mathrm{Eu}}^{154}$<0.05. All these results are believed to be good to ±15 percent.

• Received 10 February 1949

DOI:https://doi.org/10.1103/PhysRev.75.1500