Abstract
Excited states in¹⁴⁸₆₆ Dy were populated viaβ⁺/ECdecay of¹⁴⁸ᵐ Ho using the GRIFFIN spectrometer at the TRIUMF ISAC-I facility. A combined measurement of the mean lifetime of the3₁⁻level using the Generalized Centroid Difference (GCD) method and branching fraction of the3₁⁻→0₁⁺γ -ray decay has been performed. From these results, an enhanced electric octupoleB(E3;3₁⁻→0₁⁺)transition strength of 46(3) W.u. has been determined in¹⁴⁸₆₆ Dy. This is the largest measured value across the closed neutron shell atN=82and provides direct evidence of enhanced octupole collectivity beyondZ=64 . The evolution of theB(E3; 3⁻₁ → 0⁺₁)strength along theN=82isotonic chain is compared with quasiparticle random-phase approximation (QRPA) calculations using the SkI3 and SkM ^(*)Skyrme energy-density functionals, as well as with large-scale shell-model (SM) calculations. This result extends the boundaries of enhanced octupole collectivity far from the so-called `octupole magic numbers'Z=56andN=88 .