EnhancedE3Transition inLa137

Abstract

Using time-to-amplitude conversion techniques, the half-life of the 1004-keV level in ${}_{}{}^{137}{}_{}{}^{}\mathrm{La}$ was found to be ≤ (0.41±0.07) nsec. This upper limit also applies to the 836- and 926-keV levels. The 1004-keV level is depopulated by 168-, 994-, and 1004-keV $\gamma$-ray transitions. Using the corresponding experimental (previously known) branching ratios from this level, the partial half-life of the 994-keV transition, which is of $E3\mathrm{}$ character, is ≤ (0.14±0.03) μsec. The enhancement factor ($\frac{{\tau }_{\mathrm{Weisskopf}}}{{\tau }_{\mathrm{obs}}}$) is ≥7.8. This result is compared with other $E3\mathrm{}$ rates. The half-life of the 168-keV transition of $E1\mathrm{}$ character from the 1004-keV level was found to be ≤ (0.45±0.1) nsec with a resulting enhancement factor of ≥0.45×${10}^{-4\mathrm{}}$. The half-life of the 1004-keV transition is ≤ (10.3±0.3) nsec; its character is $M2\mathrm{}$ or $M2-E3\mathrm{}$, and the resulting enhancement (assuming all $M2\mathrm{}$) is ≥1.12×${10}^{-2\mathrm{}}$.