Measurements of $L$-shell internal conversion line intensity ratios are reported for the 57.37- and 293.3-keV transitions in ${}_{}{}^{143}{}_{}{}^{}\mathrm{Pr}$ and for the 145.43-keV transition in ${}_{}{}^{141}{}_{}{}^{}\mathrm{Pr}$. The measurements were made, using a 100-cm-radius iron-free $\pi \sqrt{2}$ double-focusing $\beta$ spectrometer at a resolution setting of 0.05% in momentum. Comparison with theoretical $L$-shell internal conversion coefficient ratios gives multipolarities for the 57.37-keV $\gamma$ ray of $(99.85\mathrm{}\pm 0.03)\%M1+(0.15\mathrm{}\mp 0.03)\%E2\mathrm{}$ and for the 293.3-keV $\gamma$ ray of $(63\mathrm{}\pm 4)\%M1+(37\mathrm{}\mp 4)\%E2\mathrm{}$. The measured $K$-conversion coefficient for the 57.37-keV transition is 5.64±0.34. Analysis of the ${}_{}{}^{143}{}_{}{}^{}\mathrm{Pr}$ results in combination with the 293- and 57-keV $\gamma -\gamma$ angular correlation results of other experimenters indicates a $\frac{5}{2}+$ assignment for the 57.37-keV level and a $\frac{3}{2}+$ assignment for the 350.7-keV level in ${}_{}{}^{143}{}_{}{}^{}\mathrm{Pr}$. The multipolarity of the 145.43-keV transition in ${}_{}{}^{141}{}_{}{}^{}\mathrm{Pr}$ is $(99.58\mathrm{}\pm 0.08)\%M1+(0.42\mp 0.08)\%E2$.

• Received 30 October 1967

DOI:https://doi.org/10.1103/PhysRev.168.1336