Two-Phonon Triplet inBa136and Decay ofLa136

Abstract

Over twenty $\gamma$ rays have been detected in the decay of 9.9-min ${}_{}{}^{136}{}_{}{}^{}\mathrm{La}$. A high-resolution 30-cc Ge(Li) detector was used in conjunction with a pileup-rejector network which allowed the collection of undistorted data with a 40% dead time. Analysis of these data indicate levels at ($J^{\pi }$); 818.51 ($2^{+}$), 1551.1 ($2^{+}$), 1579.01 ($0^{+}$), 2080.6 ($2^{+}$), 2128.92 ($1^{+}$), 2141.50 ($0^{+}$), 2284.5 ($0^{+}$, 1,2), 2315.42 ($0^{+}$), (2322) (?), 2485.4 ($1^{\pm }$, $2^{\pm }$), 2531.7 ($3^{-}$), (2609.9) (?), (2670.5) (?), and 2773 keV. Our results are compared to those of reaction spectroscopy. The most notable difference between our more complete data and analysis and those of previous decay-scheme studies is that we find evidence that the second $2^{+}$ state is at 1551.1 keV, and that we assign the state at 1579.01 keV to be the $0^{+}$ member of the two-phonon triplet.