A new lifetime measurement of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si3.svg"> <mml:mrow> <mml:mn>15</mml:mn> <mml:mo linebreak="goodbreak">/</mml:mo> <mml:msubsup> <mml:mn>2</mml:mn> <mml:mn>1</mml:mn> <mml:mo>−</mml:mo

A spectroscopic study of the 15 / 2 1 − isomeric state in 209 Pb has been performed to shed more light on the octupole phonons near the doubly-magic nucleus 208 Pb. Populated by neutron-transfer reactions 208 Pb( d, p ) 209 Pb*, the de-exciting nuclei of interest were measured with the SF γ NCS array, a versatile set-up comprising a silicon telescope and 60 NaI(Tl) detectors. Determined with particle- γ -ray coincidences, the branching ratio and multipolarity of the aimed γ -ray transition of the 15 / 2 1 − state in 209 Pb were found to be consistent with the literature. The state lifetime was precisely measured with the delayed coincidence method. The resulting reduced transition probability B ( E 3 , 15 / 2 1 − → 9 / 2 1 + ) = 24.2 ( 4 ) W.u. is an order of magnitude more precise than previously reported. An analysis in terms of the particle-octupole-vibration coupling model led to a reevaluation of the neutron E 3 effective charge. This new experimental result on the lifetime of the 15 / 2 1 − octupole state in 209 Pb should help future investigations to constrain the nature of states in 207,208,209 Pb.