Low-Lying Excited States in 213Rn and 215Ra

Gamma rays from low-lying levels in 213 Rn and 215 Ra have been studied following the 208 Pb( 9 Be, 4n) 213 Rn and 206 Pb( 12 C, 3n) 215 Ra reactions. Spins and parities were determined by means of the measurements of γ ray angular distributions, linear polarizations and lifetimes. Enhanced E3 transitions have been observed between the ground and the first excited state. The enhancements were as high as 38±5 for 213 Rn and 34±2 for 215 Ra in Weisskopf unit. The enhancement is qualitatively explained by the particle-vibration coupling model. Cascade E3 transitions have been observed in both nuclei. The role of the two-phonon octupole vibration has been examined in relation to these cascade E3 transitions.